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15Фталоцианины
Phthalocyanines
Шкрогэтароцмклы
Review
Обзор
http://macroheterocycles.isuct.ru
DOI: 10.6060/mhc210232d
Phthalocyanines and Naphthalocyanines with Sulfur-Containing Functional Groups: Synthesis, Preparation of Hybrid Gold Nanoparticles and Some Application Areas
T. V. Dubinina,ab@ P. I. Tychinsky,a Е. А. Gorbunova,ab and М. S. Belousov®
aDepartment of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russian Federation
^Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka, Moscow region,
Russian Federation
@Corresponding author E-mail: [email protected]
Dedicated to memory of our teacher — Professor Larisa Godvigovna Tomilova
Synthetic approaches to the phthalocyanines and their polynuclear and sandwich-type derivatives, bearing sulfur-containing functional groups, are classified. Additionally complexes, possessing an extended n-conjugation system (planar and sandwich-type 2,3-naphthalocyanines) are reviewed. Principal application areas are covered. Special attention is paid to the formation of conjugates with gold nanoparticles - prospective materials for organic electronics.
Keywords: Phthalocyanine, naphthalocyanine, gold nanoparticles, sulfur, hybrid materials.
Фталоцианины и нафталоцианины, замещенные функциональными группами, содержащими серу: синтез, получение гибридов с наночастицами золота и некоторые области применения
Т. В. Дубинина,аЬ@ П. И. Тычинский,а Е. А. Горбунова,а,ь М. С. Белоусова
Московский государственный университет имени М.В. Ломоносова, 119991 Москва, Российская Федерация ъИнститут физиологически активных веществ РАН, 142432 Черноголовка, Московская область, Российская Федерация
@Е-таИ: [email protected]
Посвящается памяти нашего учителя — профессора Ларисы Годвиговны Томиловой
Представлены синтетические подходы к фталоцианинам, их полиядерным производным и сэндвичевым комплексам, замещенным функциональными группами, содержащими серу. Дополнительно рассмотрены комплексы, обладающие протяженной системой п-сопряжения (2,3-нафталоцианины плоского и сэндвичевого типа). Рассмотрены основные области применения данных соединений. Особое внимание уделяется образованию конъюгатов с наночастицами золота - перспективным материалам для органической электроники.
Ключевые слова: Фталоцианин, нафталоцианин, наночастицы золота, сера, гибридные материалы.
Introduction
The nature of the functional groups in phthalocyanine molecules plays a crucial role in many practical applications. The introduction of electron-releasing or electron-withdrawing substituents leads to the manifestation of p- or n-type semiconductor properties, respectively.11,21 Asymmetrically substituted phthalocyanines containing both electron-rich and electron-deficient fragments are characterized by the presence of nonlinear optical properties.131 The preparation of phthalocyanines containing hydrophilic fragments offers opportunities for their use in catalysis,[4] as well as as photosensitizers in photodynamic therapy (PDT).[56] Besides, functionally substituted phthalocyanines can be used as starting compounds to create complexes of a sandwich structure.[7-11]
2,3-Naphthalocyanines are among the most widely studied and promising annelated analogs of phthalocya-nines. Expansion of the n-system leads to a bathochromic shift of the main absorption maxima up to almost 900 nm,[12] shift of the first oxidation potential to the cathode region, and enhancement of n-n interactions.[1314]
Due to the extended n-system, wide coordination possibilities and the ability to form new covalent bonds due to peripheral substituents, phthalocyanines and their analogs can form hybrid systems with nanotubes,[1516] fullerenes,[16] nanoparticles.[41718] Compared to compositions in which the components do not form chemical bonds with each other,[19] hybrid materials have several advantages. For instance, in photovoltaics the use of hybrid materials can improve the efficiency of energy transfer[20] and accordingly reduce the thickness of the photoactive layer.
Hybrids of phthalocyanines and gold nanopar-ticles are of greatest interest. In our research group[21] a hybrid of tert-butyl-substituted aluminum phthalocyanine and gold nanoparticles was obtained, for which a plasmon absorption increase at wavelengths of 535-550 nm was observed by more than 8 times. This phenomenon can lead to an increase in the yield of singlet oxygen.[22]
The presence of nanoparticles in the conjugate can provide better delivery of the photosensitizer to tumor cells during PDT.[23] Also, for such hybrid materials, enhancement of fluorescence[24] and nonlinear optical response can
be observed.[25]
For this area of research, phthalocyanines and their analogs substituted with functional groups containing sulfur are promising. They can form strong S-Au bonds due to the "soft" nature of these elements.[1718,26-28]
The purpose of this review is to systematize approaches to the synthesis of phthalocyanines and 2,3-naphthalocya-nines substituted with sulfur-containing functional groups. Methods for the preparation of phthalonitriles and 2,3-dicy-anonaphthalenes as starting compounds in the synthesis of the corresponding phthalocyanines and 2,3-naphthalo-cyanines are considered. The review presents several groups of substituted phthalocyanines and 2,3-naphthalocyanines, which can be subdivided as follows:
- free-base ligands, planar metal complexes containing one phthalocyanine or 2,3-naphthalocyanine macrocycle;
- sandwich-type double decker complexes, containing two phthalocyanine or naphthalocyanine macrocycles shar-
ing a central metal ion - diphthalocyanines and dinaphtha-locyanines respectively.
- bi- and polynuclear complexes containing two or more covalently linked phthalocyanine macrocycles.
Over the past 10 years, two reviews have been published devoted to the study of the role of substituents in the chemistry of phthalocyanines and their analogues. [2930] However, they mention only a few examples of phtha-locyanines substituted with sulfur-containing functional groups. Besides, these reviews do not provide data on the corresponding 2,3-naphthalocyanines, diphthalocyanines, and polynuclear complexes. In the review[29] methods for the synthesis of symmetrically and unsymmetri-cally substituted phthalocyanines containing sulfogroups were considered in detail; therefore, these compounds were not included in our review.
The review considers some promising areas of application of phthalocyanines substituted by functional groups containing sulfur: materials for the near-IR range, gas sensors, photovoltaics. Special attention is paid to hybrid materials based on gold nanoparticles coated with a phtha-locyanine shell.
1. Synthetic approaches to o-phthalonitriles bearing sulfur-containing functional groups
The starting compounds in the synthesis of phthalocyanines and their metal complexes are o-phthalonitriles. Varying the substituents allows to control the properties of target phthalocyanine complexes: to reduce aggrega-tion,[31] to enhance nonlinear optical[32] and semiconductor properties,[1] to create additional redox-active centers.[33] It is important to note that the introduction of substituents can be implemented in the peripheral - 4,5 and non-peripheral - 3,6 positions of o-phthalonitrile.
1.1. Nucleophilic substitution in the synthesis
of o-phthalonitriles with sulfur-containing functional
groups
The introduction of sulfur-containing functional groups into o-phthalonitrile molecules can be realized in several ways. The most common method is nucleophilic substitution. The following options for carrying out this reaction in o-phthalonitriles are described:
- substitution of nitro group;
- substitution of the halogen;
- substitution ofp-toluenesulfonyl group;
- nucleophilic substitution reactions in an ionic liquid.
The substitution of the nitro group in 4-nitrophthalo-
nitrile with various thiols takes place at room temperature, the reaction time is 14-29 h. Potassium carbonate is used as a base (Scheme 1).
Using this technique, various alkylthio- and arylthio-substituted phthalonitriles 1 were obtained in high yields (Table 1).
The simplicity of this reaction is since the substrate is activated to nucleophilic substitution by the cyano group, which is located in the para-position to the nucleofuge.
Scheme 1.
M. Mayukh et al.[39] managed to increase the yield of nitrile 2c. A decrease in the yield of hexylthio-substituted nitrile 2a with an increase in the reaction temperature may be due to a change in the method of isolation of the target compound. A.G. Gurek et al.[38] used recrystallization while M. Mayukh et al.[39] isolated nitrile 2a using column chromatography.
Table 1. Reaction time and yields of compounds 1a-f, obtained via Scheme 1.
Compound R Reaction time, h Yield, % Reference
1а С8Н17 18 83 [34]
1b Ph 14 85 [35]
1c PhCH2 14 92 [35]
1d 29 90 [36]
1e С12Н25 18 62 [37]
1f С16Н33 18 66 [37]
The starting compound in the synthesis of dialkylthio-substituted o-phthalonitriles 2a-h can be 4,5-dichlorophtha-lonitrile (Scheme 2).
Scheme 2.
The reaction is carried out at a temperature not higher than 90 °C, in the presence of potash. DMSO or N,N-dimethylacetamide is used as a solvent (Table 2).
In N,N-dimethylacetamide, the reaction time is significantly shorter than in the syntheses carried out in DMSO. However, by carrying out the reaction in a DMSO medium,
It was found, that[34,42] 4,5-diiodophthalonitrile can be used as starting compound in the synthesis of 1,2-dicyano-4,5-phenylthio and 1,2-dicyano-4,5-p-tolylthiobenzenes 3a and 3b, respectively (Scheme 3).
Scheme 3.
It is interesting to note that the reaction was carried out with heating, in contrast to the method described
Table 2. Reaction conditions and yields of compounds, obtained via Scheme 2.
Compound R Reaction conditions Yield, % Reference
2а C6H13 DMSO, K2CO3, RT, 14 h 79 [38]
2а C6H13 DMSO, K2CO3, 80 °C, 12 h 70 [39]
2b C7H15 DMSO, K2CO3, 80 °C, 12 h 84 [39]
2c C8H17 A^-Dimethylacetamide, K2CO3, 90 °C, 6 h 79 [34]
2c C8H17 DMSO, K2CO3, 80 °C, 12 h 86 [39]
2d C9H19 DMSO, K2CO3, 80 °C, 12 h 78 [39]
2e C10H21 DMSO, K2CO3, 80 °C, 12 h 76 [39]
2f C12H25 DMSO, K2CO3, RT, 14 h 80 [38]
2g C16H33 jV,jV-Dimethylacetamide, K2CO3, 70 °C, 6 h 79 [40]
2h Pri A^-Dimethylacetamide, K2CO3, 100 °C, 6 h 75 [41]
by the authors[38] (Table 2). In this case, the target compounds were obtained in high yields, and the reaction time was reduced to 30 min.
The introduction of phenylthio groups into non-peripheral positions 3,6 was carried out in DMSO at room temperature (Scheme 4).[43]
liquid can be classified as basic/strongly coordinating. Thus, Bu4NBr plays a double role in the nucleophilic substitution reaction: the medium and the base.
Using this approach, a number of alkylthio-substituted phthalonitriles was obtained (Table 3). All reactions were carried out at a temperature of 100 °C approximately corresponding to the melting point of Bu4NBr (m.p. 102-106 °C). Thiol is taken in two-fold excess. At a lower temperature (90 °C) and using a stoichiometric amount of the starting thiol, the yields are reduced by several times.[45]
In the case of di- and tetrasubstituted phthalonitriles, the reaction yields are decreased. In addition, to replace chlorine atoms in 4,5-dichlorophthalonitrile, an additional introduction of two equivalents of potash is required.
Scheme 4.
In this case, p-tolyl sulfonate (OTs) was used as a leaving group. The yield of the target compound is comparable to the yield of compound 3a, which contains phenylthio substituents at the 4,5 positions.
Due to its high ionic conductivity,[44] ionic liquids can increase the activity of nucleophiles in reactions proceeding by SNAr mechanism. The melt of inexpensive and fairly stable ionic liquid Bu4NBr was chosen by P.-C. Lo et al. [45] as a medium for nucleophilic substitution. According to the classification presented in the review [46] this ionic
1.2. Suzuki reaction in the synthesis
of o-phthalonitriles with sulfur-containing functional
groups
A method for introducing functional groups containing sulfur into phthalonitrile by Suzuki cross-coupling reaction is presented in the literature. Trifluoromethanesulfonate was introduced into the molecule as a leaving group (Scheme 5).[47] This choice is due to the availability of the parent phenol. In addition, the rate-limiting stage of the Suzuki reaction is often oxidative addition; therefore, the relative activity of substrates decreases in the row of substituents: I > OTf > Br >> Cl.[48] It is also important to note that electron-
Table 3. Reagents and yields of target compounds when carrying out nucleophilic substitution in the melt of Bu4NBr.
[45]
Initial phthalonitrile
Thiol
Product
Yield, %
Cl
CN
CN
CN
CN
CN
CN
NO2
CL ^ CN
CN
CN
VCN
C8H17SH
C12H25SH
C8H17SH
C12H25SH
C8H17SH
C8H17SH
CN
CN
CN
C8H17S
Ci2H25S- "*CN
^CN
CN
CN CN
C12H25
77
79
91
93
50
55
F
F
F
withdrawing substituents (for example, cyano groups) activate halides and pseudohalides to oxidative addition. S. Al-Raqa[47] used tetrakis(triphenylphosphine) palladium as a catalyst.
Starting from 4,5-dichlorophthalonitrile and 3-(ethyl-thio)phenylboronic acid under the conditions of the Suzuki cross-coupling reaction, we obtained substituted phthaloni-trile 5 (Scheme 6).[49] It is well known that cross-coupling reactions for aryl chlorides are ineffective and require the addition of special ligands (P(But)3; tricyclohexylphos-phine (PCy3)).[50-52] Due to steric hindrance, such ligands promote the dissociation of the complex of zero-valent palladium entering the catalytic cycle to a coordinatively unsaturated state, for example: Pd(PBut3). In addition, their electron donating properties facilitate the oxidative addition step.[52]
However, the presence of electron-withdrawing CN groups in the molecule leads to the activation of 4,5-dichlorophthalonitrile to oxidative addition.[4851] This allowed us to use only dichlorobis(triphenylphosphine) palladium as
a catalyst, without introducing additional ligands. It is important to note that the synthesis of diaryl-substituted o-phtha-lonitriles was carried out from 4,5-dichlorophthalonitrile, using Pd(II) as a catalyst, in the presence of 2-(2',6'-dime-thoxybiphenyl)dicyclohexylphosphine (S-Phos).[50] We were lucky to obtain nitrile 5 without the introduction of S-Phos and in a higher yield.
A study of the influence of the molar ratio of the starting reagents on the yield of the target nitrile 5 was carried out. It was shown that the use of a molar ratio of 1:4 (4,5-dichlorophthalonitrile : 3-(ethylthio)phenylboronic acid), which was previously used in our scientific group for the synthesis of 4,5-diphenylphthalonitrile,[53] results in the formation of a mixture of mono- (6) and disubstituted (5) compounds (Table 4). It is very difficult to separate these compounds, since their Rf values are close.
An increase in the amount of 3-(ethylthio)phenyl-boronic acid (molar ratio 1:6, 4,5-dichlorophthaloni-trile : 3-(ethylthio)phenylboronic acid) led to the selective formation of nitrile 5.
Table 4. Reaction conditions and the yields for Scheme 6.[49]
Yield, %
Molar ratio of 4,5-dichlorophthalonitrile : 3-(ethylthio)phenylboronic acid -
5 6
1:2.5 0 19
1:4 37a 16a
1:6 70 0
a — yields calculated from 'H NMR spectroscopy data.
Scheme 7.
It was found that when a 2.5 fold molar excess of aryl-boronic acid was used, compound 6 was formed.
1.3. Synthesis of sulfonyl substituted o-phthalonitriles
An important feature of functional groups containing sulfur is the possibility of changing the oxidation state of sulfur (Scheme 7). Sulfonyl-substituted phthalonitriles 7 are easily and in high yields obtained by the oxidation reaction of alkylthio-substituted phthalonitriles.[34]
When using hydrogen peroxide in acetic acid, the reaction is carried out first at 90 °C for 4 hours and then stirred overnight at room temperature. When using meta-chloroperbenzoic acid, the reaction mixture is kept at room temperature for 2 days.
2. Synthesis of 2,3-dicyanonaphthalenes with sulfur-containing functional groups
The closest analogues of phthalocyanines with an extended п-system, 2,3-naphthalocyanines, can be synthesized on the basis of substituted 2,3-dicyanonaph-thalenes.[14] Previously, only one approach to the synthesis of 2,3-dicyanonaphthalenes substituted with functional groups containing sulfur was described in the literature.[54-57] Bromo-substituted 2,3-dicyanonaphthalenes 8, which are
obtained starting from bis(dibromomethyl)benzenes, are used as the initial compound.[14,58] These tetrabromides under the action of sodium iodide are converted into o-qui-nodimethanes 8', which enter into the Diels-Alder reaction with fumaronitrile. In this case, tetralins 8'' are formed, which are aromatized to the target compounds with the formation of an energetically favorable naphthalene n-system. The resulting naphthalodinitrile 8 reacts with alkyl thiolates (Scheme 8)
Alkylthio- and arylthio-substituted 2,3-dicyanonaph-thalenes 9 obtained from compounds 8a,b are presented in Table 5. Copper salts of alkylthiols,[54'5557] or thiolate obtained by the action of 1,8-diazabicyclo[5.4.0]undecene-7 (DBU)[56] were used in the synthesis (Table 5). Copper salts of alkyl thiols can be formed in situ or can be prepared and isolated in advance. The synthesis of copper salts of alkyl thiols was carried out in boiling ethanol by analogy with the procedure for the synthesis of copper n-butyl mercaptide from Cu2O and the corresponding alkyl thiol.[59]
The decrease in the yields of the nucleophilic substitution reaction (up to 30 % in the case of compound 9h), as compared to o-phthalonitriles, is probably since the cyano groups activating the substitution are distant one benzene ring from the nucleophile attack site. The authors managed to achieve the best yields.[55]
Based on 2,3-dicyanonaphthalene 8b by the Suzuki reaction, we selectively obtained 3-(ethylthio)phenyl-substituted nitrile 10 (Scheme 9).[49]
8a: R1=H; R2=Br (92%); 8b: R1=R2=Br (95%)
Scheme 8.
Table 5. Reaction conditions and the yields of 9a-h, obtained via Scheme 8.
Compounds R3 R4 Reaction conditions Yield, % Reference
9a C10H21S H CuR3; quinoline; Py; A; 6h 53 [54]
9b C6H13S H CuR3; quinoline; Py; A; 6h 52 [54]
9c C4H9S H CuR3; quinoline; Py; A; 6h 70 [54]
9d C16H33S H CuR3; quinoline; Py; A; 6h 58 [54]
7e 0 \ H CuR3; quinoline; Py; A; 6h 46 [54]
9f C3H7S C3H7S C3H7SNa; Cu2O; DMF; A; 3h 89 [55]
9g PhS PhS PhSNa; Cu2O; DMF; A; 3h 84 [55]
9h C12H25S C12H25S C12H25SH; DBU; DMF; 90 °C; 6h 65 [56]
9h C12H25S C12H25S C12H25SNa; Cu2O; solvent 30 [57]
and temperature not specified
In the synthesis, the ratio of reagents selected for 3-(ethylthio)phenyl substituted phthalonitrile 5 was used. However, a mixture of 1,4-dioxane : acetonitrile was used as a solvent, since the initial 6,7-dibromo-2,3-dicya-nonaphthalene is poorly soluble in pure 1,4-dioxane.
3. Synthesis of phthalocyanines bearing the sulfur-containing functional groups
3.1. Synthesis, based on o-phthalonitriles
To obtain phthalocyanines substituted with functional groups containing sulfur, and their metal complexes, the template method is most often used. The starting
Ri 11
compounds are the corresponding o-phthalonitriles 11. The synthesis is carried out in boiling solvents or in melts (Scheme 10, Table 6).
1,8-Diazabicycloundec-7-ene (DBU) can be used as the base initiating the cyclization process^38'60,62 Probably, in these cases, alcoholates are not used as bases due to possible transesterification processes.
Two high-temperature methods for the synthesis of phthalocyanine ligands substituted by sulfur-containing groups are described (Table 6).[373841] In the method described by I. Gurol et al.p7] freshly distilled hydroqui-none was used as a redox-active particle and simultaneously a source of protons to obtain ligand 12a. In the process of template cyclization of the phthalocyanine macrocycle, the 18 n-electron system is formed from the 16 n-electron
12-24
Table 6. Reaction conditions and the yields of 12-24, obtained via Scheme 10.
Compounds R M Reaction conditions Yield, % Reference
12a R2 = CAA R1 = R3 = R4 = H HH Hydroquinone, 200 °C, 5 h 24 [37]
12b R2 = C12H25 S, R1 = R3 = R4 = H Ni NiCl2, quinoline, 200 °C, 5 h 26 [37]
12c R2 = C16H33S, R1 = R3 = R4 = H Ni NiCl2, quinoline, 200 °C, 5 h 34 [37]
13a R2 = R3 = C6H13S, R = R4 = H HH Pentanol, DBU, A, 60 h 39 [38]
13b R2 = R3 = C6H13S, R1 = R4 = H Ni NiCl2, quinoline, 200 °C, 5 h 38 [38]
13c R2 = R3 = C12H25^ R1 = R4 = H Ni NiCl2, quinoline, 200 °C, 5 h 19 [38]
13d R2 = R3 = C6H13S, R1 = R4 = H Cu CuCl2, urea, 100 0C, 2 h 62 [38]
13e R2 = R3 = C6H13^ R1 = R4 = H Co CoCl2, ethylene glycol, 200 °C, 4 h 26 [38]
13f R2 = R3 = C6H13S, R = R4 = H Zn ZnCl2, quinoline, 200 °C, 6 h 48 [38]
14a R1 = PhS, R2 = R3 = R4 = H TiO Ti(OBu)4, C8H17OH, urea, 150 °C, 14 h 40 [35]
14b R1 = PhCH2S, R2 = R3 = R4 = H TiO Ti(OBu)4, C8H17OH, urea, 150 °C, 14 h 43 [35]
14c R2 = PhS, R1 = R3 = R4 = H TiO Ti(OBu)4, C8H17OH, urea, 150 °C, 14 h 52 [35]
14d R2 = PhCH2S, R1 = R3 = R4 = H TiO Ti(OBu)4, C8H17OH, urea, 150 °C, 14 h 48 [35]
15a R,=
R;=R3=R4=H
Zn
Zn(OAc)2, n-hexanol, A, DBU, 18 h
15b R3=R= S
R = R4 = H
16a R2 = Ci6H33S,
R = R3 = R4 = H 16b R2 = R3 = C6H13S, R1 = R4 = H
2 3 6 13 ' 1 4
Zn Zn(OAc)2, «-hexanol, A, DBU, 18 h
Pb
Pb
PbO, 210 °C, 5 h
PbO, 210 °C, 5 h
33
18 19 26
17 R2 = R3= S%,R = R=H HH DBU, pentanol, A, 8 h 40 [41]
18a R2 = R3 = C8H17S, R = R4 = H Cu CuCl2, DBU, n-hexanol, A , 24 h 58 [62]
18b R2 = R3 = C16H33S, R1 = R4 = H Cu CuCl2, DBU, n-hexanol, A , 24 h 23 [62]
18c R3 R1 =R = 2 = R4 = H , Cu CuCl2, DBU, n-hexanol, A , 24 h 52 [62]
19a R1 = R4 = R2 = R3 = H VO VCl4, DBU, pentanol, A , 6 h 42 [63]
19b R1 = R4 = С5Н11S, R2 = R3 = H Mn(OAc) Mn(OAc)3, DBU, pentanol, A , 6 h 42 [64]
19c R1 = R4 = С5Н11S, R2 = R3 = H TiO Ti(OBu)4, DBU, pentanol, A , 6 h 22 [64]
20 R2 = PhS, R1 = R3 = R4 = H Pd PdCl2, urea, 190 0C, 12 h 72 [65]
21a R2 = R3 = C6H13S, R1 = R4 = H TiO Ti(OPr')4, urea, melt, 150 °C, 24 h 16 [39]
21b R2 = R3 = C7H15S, R1 = R4 = H TiO Ti(OPr')4, urea, melt, 150 °C, 24 h 42 [39]
21c R2 = R3 = C8H17S, R = R4 = H TiO Ti(OPr')4, urea, melt, 150 °C, 24 h 34 [39]
21d R2 =R3 = C9H19S, R1 = R4 = H TiO Ti(OPr')4, urea, melt, 150 °C, 24 h 42 [39]
21e R2 = R3 = C10H21S, R1 = R4 = H TiO Ti(OPr')4, urea, melt, 150 °C, 24 h 35 [39]
22a R2 =R3 = 3-(ethylthio) phenyl, R1 = R4 = H Zn Zn(OAc)22H2O, Am'OH, A, MeOLi, 5 h 88 [49]
22b R2 R21 = 3-(ethylthio) phenyl R3 = Cl =R4 =H Zn Zn(OAc)22H2O, Am'OH, A, MeOLi, 5 h 55 [49]
22c R2 = R3 = 3-(ethylthio) phenyl, R1 = R4 = H Er(OAc) Er(OAc)34H2O, Am"OH, A, MeOLi, 4 h 91 [66]
22d R2 = R3 = 3-(ethylthio) phenyl, R1 = R4 = H Lu(OAc) Lu(OAc)34H2O, Am"OH, A, MeOLi, 4 h 70 [66]
60
60
61
61
(continued) 21
Phthalocyanines and Naphthalocyanines with Sulfur-Containing Functional Groups Table 6. Continued.
23a
23b
24
R2=R3 = ^ S%'R1=R4=H
= R
2 3
.X
R2= s%= R1=R3=R4=H
h2nvn sv
T T
R= nh2 , R1=R4=Rj=H
HH 1) LDA/THF, 25 0C, 3 h; 2) H+/H20 19.2
HH 1) LDA/THF, 25 0C, 3 h; 2) H+/H20 27
Zn Zn(OAc)2, n-hexanol, A, DBU, 6 h 48
[67]
[67]
[68]
system consisted from four isoindole fragments. I. Gurol et al.[37] suggest that hydroquinone is a reducing agent.
In the second method[38,41] the synthesis of the ligands 13a and 17 was carried out under milder conditions - boiling pentanol (138 0C) and DBU, as a base. Compared to the first method, the yield of the target ligand is more than 1.5 times higher. Probably, the decrease in the yield in the first case is due to the polymerization of the nitrile under harsh conditions of the synthesis.
An interesting example of low-temperature synthesis of phthalocyanine ligands was realized by the authors.[67] The reaction was carried out in THF at room temperature, in the presence of lithium diisopropylamide (LDA) as a base. Compared to lithium methoxide, diisopropylamide is more basic. Its main disadvantage is steric hindrance created by isopropyl fragments. However, they are insignificant in the formation of the phthalocyanine macrocycle. This is due to the flat structure of the cyano group, which is attacked by the nucleophile during template cycliza-tion.[67]
When obtaining metal complexes, we have achieved the best yield for erbium and lutetium complexes[66] using boiling AmiOH and lithium methoxide as base.
For titanium complexes, carrying out the reaction in solution,[35] as a rule, leads to higher yields of the target compounds, in comparison with the synthesis in the melt in the presence of urea.[39]
The synthesis of thiophene-substituted complexes 25a-c was carried out using the template method (Scheme 11). 2-Ethoxyethanol was used as a solvent, and DBU as a base. The main peculiarity of approach used by the authors[69] is that the starting thiophene-substituted phthalonitrile was obtained from the corresponding dibromo derivative without isolation of intermediate compounds. The choice of such a strategy is since at the first stage (cross-coupling according to Suzuki), in addition to the target disubstitution product, Z. Chen et al.m obtained a monosubstitution product, and also isolated a part of the unreacted starting compound. These substances have the same Rf values and cannot be separated chromatographically; therefore, the undivided reaction mass was introduced into the hydrolysis reaction (second stage, Scheme 11). Separation was carried out at the stage of nitrile preparation (Scheme 11, insert). For this, the reaction mass was treated with an excess of hydroquinone in the presence of potash.
The obtained products of the reaction of nucleophilic substitution are easily separated from the target phthaloni-trile in an aqueous alkali solution. The total yield of nitrile was 19%.
Metal complexes of phthalocyanines substituted with sulfur-containing functional groups can be obtained not only by the template cyclization method, but also by the metalla-tion reaction of the phthalocyanine ligand (Scheme 12).[4170]
Ligand 27 was prepared[41] from the corresponding nitrile (Table 6). Metallation was performed with lead or copper acetates in boiling DMF.
In the second case,[70] 4-octylthio-substituted phtha-lonitrile was used as the starting compound, which was introduced into the reaction of template synthesis with lead oxide. The reaction medium was the melt of initial nitrile. The lead phthalocyaninate 26 was treated with acetic acid to form ligand 26'. The last stage was the metallation of ligand 26' in boiling «-hexanol. Copper phthalocyaninate 27 was obtained in high yield. This compound, due to the different positions of the peripheral substituents, is a mixture of isomers. It is important to note that complex 26 and ligand 26' were introduced into the reaction without preliminary purification; therefore, their yields were not calculated.
The total yields of copper complexes 17a and 27, starting from the corresponding substituted nitriles, are 34% and 85%, respectively. The low total yield of the first approach is due to losses at the stage of isolation of ligand 17 by the template method.
Nombona et al.[36] described an example of the synthesis of unsymmetrically substituted phthalocyanine ligand of A3B type. This classification is based on the number of fragments of the two nitriles that make up the phthalo-cyanine macrocycle. The target compound was obtained by a statistical condensation reaction between two different nitriles (Scheme 13). Dilithium complex was obtained in situ,[36] and then demetallated by acetic acid. Interestingly, to achieve the best contact between nitriles 28 and 29, they were mixed and ground in a mortar before being dissolved in pentanol.
The yield of the target ligand 30 was 13%. The low yield is due to the formation of difficult-to-separate self-cyclization by-products of starting compounds 28 and 29. A few more examples of A3B phthalocyanines will be given in Section 3.2.
3.2. Modification of substituents at the stage of cyclization of the phthalocyanine macrocycle and in the formed macrocycle
The literature describes examples of the introduction of functional groups containing sulfur into the phthalo-cyanine molecule both at the stage of template cyclization of the macrocycle and in the formed phthalocyanine.
Scheme 11.
17a: M = Cu, n = 1 (85%); 17b: M = Pb, n = 3 (80%)
CuCI2, n-hexanol, A, 2h
27 (89%)
Scheme 12.
P.-C. Lo et al.[45] succeeded in synthesizing alkylthio-substituted phthalocyanines 31 in an ionic liquid starting from 4-nitrophthalonitrile (Scheme 14). Alkylthiol was introduced into the reaction in a fourfold excess. The reaction was carried out at a temperature of 100 °C approximately corresponding to the melting point of Bu4NBr (m.p. 102-106 °C, decomposes at 133 °C). The use of a twofold excess leads to the formation of a nucleophilic substitution reaction product.
Thus, both the formation of a macrocycle and the reaction of nucleophilic substitution of the nitro group took place during the synthesis. A similar reaction for 3-nitroph-thalonitrile results in only trace amounts of the target phthalocyanine ligand.
It is important to note that the yield of phthalocyanine 31b when using a one-step technique (method A, Scheme 14) is higher than when using a two-step approach (total yield - 16%).[45]
The approach described by the N. Nombona et al.[36] includes: synthesis of a zinc complex with a terminal hydroxy group, introduction of a protective group, alkyla-tion of thiourea with compound 32, and hydrolysis to form a terminal SH group. The introduction of terminal thiol
groups is necessary for the further formation of covalent bonds with gold nanoparticles. Scheme 15 shows the overall yield for complex 33. Intermediates were not isolated and characterized.
Alternative method (method B, Scheme 15) of conversion of OH groups to SH was demonstrated by D.O. Oluwole et al. This approach includes substitution of iodine atoms with thiourea or thiobenzoyl fragments. In the case of thiobenzoyl group the last stage implied mild cleavage of benzoyl protective groups.[71] Due to the presence of thiol groups, this phthalocyanine could be conjugated with triocylphosphineoxide-capped CdSe quantum dots or oleylamine capped silver nanoparticles (Ag-NPs). These conjugates possess enhanced nonlinear optical response in comparison with individual components.
It was found by A.V. Shokurov et al.,[72] that thiobenzo-ate-bearing phthalocyanine have a tendancy to form densely packed self-assembled monolayers on gold without the need in additional ex situ deprotection synthetic step.
Carboxyl-substituted А3В phthalocyanine appears to be initial compound for the introduction of thiol-containing spacer, which was useful for the preparation of hybrid nanoparticles.[36] Zinc complex 34 bearing three
Scheme 15.
Scheme 16.
a-naphthoxy-groups and one carboxyl group was activated by dicyclohexyl carbodiimide (DCC) and then the amide bond was formed (Scheme 16).
The synthesis of A3B phthalocyanine with three decyl-substituted moieties and one thiol functional group in nonperipheral (a-position) of phthalocyanine macrocycle was carried out by I. Chambrier et al.[73] (Scheme 17). Heptadecyl-hydroxypropyl-substituted zinc phthalocyanine
36 was chosen as initial compound.
Then by the analogy with approach, which was depicted in Scheme 15 (method A),[36] the protective group was introduced and the alkylation of thiourea by compound
37 was realized. All intermediate compounds were isolated and characterized. Target compound 38 was isolated using column chromatography and subsequent recrystallization.
4. Synthesis of lanthanide(III) diphthalocyanines bearing sulfur-containing functional groups
All methods described in the literature for the synthesis of lanthanide(III) diphthalocyanines with sulfur-containing functional groups include the use of corresponding substituted phthalonitriles as starting compounds (Scheme 18, Table 7).
Diphthalocyanines and their analogs (dinaphthalo-cyanines) exist in the form of stable n-radicals.[7,74,81-84] The radical is delocalized between the pyrrole fragments of the phthalocyanine macrocycle.
The rather low yield of target compounds 39-43 is probably due to: (1) the formation of by-products of the polymerization of the starting nitriles, (2) steric hindrances created by DBU, coordinating with the central lanthanide ion during the reaction.[7,85]
39-43
Scheme 18.
Using electrochemical measurements,[74] it was found that complex 39 is easier to reduce and more difficult to oxidize than the corresponding unsubstituted diphthalo-cyanine. On this basis, phenylthio-substituents in this case refer to electron-withdrawing ones.
In the case of complex 41a, the compliance with the declared structure can be questioned. This compound was not characterized by either mass spectrometry or 1H NMR spectroscopy. The hypothesis of the n-radical nature of the obtained compound is based on the presence of a low-intensity broadened absorption band at 440 nm[76] and is not confirmed by the data of electron paramagnetic resonance (EPR) spectroscopy.
An important representative of the class of diphthalo-cyanine complexes of a sandwich structure are heteroleptic complexes. This review considers heteroleptic complexes containing phthalocyanine ligands with various substituents.
The authors of [74] described the synthesis of a hetero-leptic diphthalocyanine complex 44 containing an unsubsti-tuted phthalocyanine and octaphenylthio-substituted decks (Scheme 19).
R
N.
J\l
Ri
MesCI, CH2CI2 ^jH '-N-' Rl
-----Et3N, 10 C-RT -
Ri R. °
1)THF, EtOH
2)thiourea
3)NaOH ^
Ri
36: R1 — C^qH2-|J n—3
Rt
37: R., =C10H21; n=3 (98%)
^N.N^(CH2)nSH
R
R!
38: R., =C10H21; n=3 (77%)
Table 7. Reaction conditions and yields of compounds 39-43, obtained via Scheme 18.
Compound R R' Ln Reaction conditions1 Yield, % Reference
39 PhS PhS Eu Eu(acac)3nH2O, pentanol, A 42 [74]
40a R Eu Eu(acac)3nH2O, hexanol, A 10.52 [75]
40b R Yb Yb(acac)3nH2O, hexanol, A 11.54 [75]
40c R Lu Lu(acac)3nH2O, hexanol, A 12.71 [75]
41a h2n -ÇT* nh2 H Lu Lu(OAc)32H2O, hexanol, A 49 [76]
41b C8H17S C8H17S Eu Eu(OAc)34H2O, hexanol, A 61 [77]
41c C10H21S C10H21S Eu Eu(OAc)34H2O, hexanol, A 15 [77]
41d C12H25S C12H25S Eu Eu(OAc)34H2O, hexanol, A 44 [77]
41e C14H29S C14H29S Eu Eu(OAc)34H2O, hexanol, A 43 [77]
41f C16H33S C16H33S Eu Eu(OAc)34H2O, hexanol, A 40 [77]
41g C8H17S C8H17S Tb Tb(OAc)34H2O, hexanol, A 19 [77]
41h C10H21S C10H21S Tb Tb(OAc)34H2O, hexanol, A 39 [77]
41i C12H25S C12H25S Tb Tb(OAc)34H2O, hexanol, A 42 [77]
41j C14H29S C14H29S Tb Tb(OAc)34H2O, hexanol, A 44 [77]
41k C16H33S C16H33S Tb Tb(OAc)34H2O, hexanol, A 32 [77]
41l C18H37S C18H37S Tb Tb(OAc)34H2O, hexanol, A 22 [77]
41m C8H17S C8H17S Lu Lu(OAc)34H2O, hexanol, A 8 [77]
41n C10H21S C10H21S Lu Lu(OAc)34H2O, hexanol, A 9 [77]
41o C12H25S C12H25S Lu Lu(OAc)34H2O, hexanol, A 28 [77]
41p C14H29S C14H29S Lu Lu(OAc)34H2O, reKcaHOJi, A 16 [77]
41q C16H33S C16H33S Lu Lu(OAc)34H2O, hexanol, A 20 [77]
41r C18H37S C18H37S Lu Lu(OAc)34H2O, hexanol, A 44 [77]
42a C6H13S C6H13S Gd Gd(OAc)3, hexanol, A 29 [78]
42b C6H13S C6H13S Dy Dy(OAc)3, hexanol, A 36 [78]
42c C6H13S C6H13S Sm Sm(OAc)3, hexanol, A 30 [78]
43a C6H13S H Lu Lu(OAc)3, pentanol, A 12 [79]
43b C8H17S H Lu Lu(OAc)3, pentanol, A 14 [79]
43c C10H21S H Lu Lu(OAc)3, pentanol, A 13 [79]
43d C12H25S H Lu Lu(OAc)3, pentanol, A 8.1 [79]
43d C12H25S H Lu Lu(OAc)3, hexanol, A 8.1 [80]
43e C16H33S H Lu Lu(OAc)3, pentanol, A 12 [79]
a - DBU was chosen as a base.
Scheme 19.
This compound was obtained in two stages. First, the synthesis of the monophthalocyanine complex 44' was carried out, and then the template assembly of the second phthalocyanine macrocycle and the formation of the target compound 44.
The authors of [86] have synthesized heteroleptic diph-thalocyanine complexes of europium 45 and 46 (Scheme 20). The authors classify these compounds as AjB type.
The synthesis was carried out under the conditions of a statistical condensation reaction by mixing two nitriles in a ratio of 20:1 (A:B). The target compounds were purified by column chromatography. Only the corresponding symmetrically substituted diphthalocyanines were isolated as by-products. In order to show the synthetic potential of the terminal hydroxy groups, the authors
additionally carried out their modification into azido groups and methanesulfonyl groups.
5. Synthesis of 2,3-naphthalocyanines bearing sulfur-containing functional groups
The literature describes only a few examples of synthesis of 2,3-naphthalocyanines substituted with functional groups containing sulfur. Scheme 21 shows the synthesis of silicon naphthalocyaninates 47.
As a starting compound, the authors of [54] used not 2,3-dicyanonaphthalenes, but diiminoisoindolines, which are more active in the process of macrocyclization. This
Scheme 21.
approach was used to synthesize a series of alkylthio-substituted silicon naphthalocyaninates. Unfortunately, the exact yields of the target compounds were not presented in the work.
The authors of [55,56] carried out the synthesis of naph-thalocyanine complexes under milder conditions (Scheme 22, Table 8): boiling 1-pentanol or 1-hexanol. Both the diimi-noisoindoline derivative (1) and the corresponding nitrile (2) were used as starting compounds.
Using isoamyl alcohol as a solvent and lithium methox-ide as a base, we managed to obtain 3-(ethylthio)phenyl-substituted zinc naphthalocyaninate 48e[49] with a yield of 90%, which is significantly higher than those presented earlier for 2,3-naphthalocyanines substituted by functional groups containing sulfur.
The authors of [87] described the synthesis of dodec-ylthio-substituted dinaphthalocyanine europium 49 with a sandwich structure (Scheme 23).
This compound, like diphthalocyanine, is a stable n-radical. This is confirmed by the data of the EPR spectrum
recorded in toluene. The spectrum contains a structureless singlet with a g-factor of 2.01.
It is interesting to note that a higher-boiling solvent (octanol, 195 0C) was used in the synthesis of dinaphtha-locyanine 49 than in the synthesis of diphthalocyanine 41d (hexanol, 157 0C).[77] In this case, the output of compound 49 is almost twice as high.
6. Synthesis of bi- and polynuclear phthalocyanines
The main method for the synthesis of binuclear complexes is statistical condensation between the nitrile, which forms the periphery of the binuclear complex, and the compound, which forms the spacer.[14] Using this approach, the authors of [88] obtained binuclear cobalt complexes containing amino, nitro-, and ferrocenyl groups at the periphery of the macrocycle (Scheme 24).
Table 8. Reaction conditions and yields of compounds 48, obtained via Scheme 22.
Compound R M Reaction conditions Method Yield, % Reference
48a C3H7S Zn Zn(OAc)2 2H2O; DBU; 1-hexanol; Д; 5h (2) 53 [55]
48b PhS Zn Zn(OAc)2 2H2O; DBU; 1- hexanol; Д; 5h (2) 48 [55]
48c C12H25S HH DBU; 1-pentanol; Д; 10h (1) 38 [56]
48d C12H25S Cu CuCl; DBU; 1- pentanol; Д; 10h (2) 41 [56]
48e 3-(ethylthio)phenyl Zn Zn(OAc)2 2H2O; MeOLi; Am'OH; Д; 6h (2) 90 [49]
Scheme 23. Scheme of synthesis of dinaphthalocyanine complex 49. Insert - EPR spectrum of a solution of dinaphthalocyanine 49 in toluene.
Tetracyanobenzo(1,4,7,10-tetrathio(12-crown)) 50 was used as a starting compound to create a spacer. In contrast to nitro-substituted 51 and amino-substituted complexes 52, compound 53 was found to be insoluble in organic solvents. Its structure was confirmed by the data of elemental analysis and IR spectroscopy (on the disappearance of vibrations of aldehyde and amino groups).
Based on the asymmetrically substituted monophtha-locyanine complex of zinc 54 and the binuclear complex 51, a polynuclear complex 55 was obtained.
During the synthesis, the nitro groups were transformed in situ to amino groups, and then azo spacers were formed. The good solubility of the target complex 55 was presumably provided by hexylthio groups.
Despite the fact that the authors of883 postulate the overlap of the n-systems of the macrocycles of compound 55, no absorption bands in the near IR range are observed in its electronic absorption spectrum (UV-Vis). This may be due to either the aggregation of this complex as it was observed for other polynuclear phthalocyanines,[14] or to its insufficient purity.
The synthesis of the tetranuclear complex 56 based on the corresponding binuclear complex is based on a similar principle for creating an azo spacer (Scheme 26).[89]
An interesting example of a complex containing both sandwich and binuclear structural units was obtained.[90]
Compound 57 was used as the initial binuclear complex. The corresponding binuclear free ligand and its hexylthio-substituted cobalt complex are also described in the literature.[91,92]
The sandwich-type complex 58 was obtained by the interaction of the binuclear complex and diimi-noisoindoline 57'. Lithium amylate formed in situ served as the base. We assume that, based on the UV-Vis data of compound 58, it may contain an admixture of the initial binuclear complex and/or lutetium diphthalocyanine. This research group has published a number of works on sandwich complexes containing common calixarene and hetero-aromatic bridges.[93-95] A detailed analysis of these studies is given in the review.[7]
As a conclusion to this section, it can be noted that the low yields of bi- and polynuclear complexes obtained
Scheme 25.
Scheme 26.
(OAc) (OAc)
Lu Lu
HN NH NH r2^2
hn т л T:T:NH +
ч _P kiu
HN NH 57' NH
R2-C6H13S r2 57 (19.23%)
W^f N ^ R2 2 Nr^N K2
н£Ы2 r2
Lu Lu
l%\ 114 г-»
_ MKi&fl О—о___И £ rfcfL^Rj
R2 r2 58 (34.40%) R2
Scheme 27.
by the statistical condensation reaction are due to the close reactivity of the starting nitriles (forming the periphery of the binuclear complex and the spacer). This leads to the formation of the corresponding monophthalocyanines as by-products, as well as oligomers of the starting nitriles.[14]
7. Application areas of phthalocyanines
and 2,3-naphthalocyanines with functional groups
containing sulfur
The introduction of functional groups containing sulfur into the molecules of phthalocyanines and 2,3-naphtha-locyanines gives them properties that are important for their practical application.
First, due to the high affinity between sulfur and gold,[17,26] it is possible to obtain hybrids with gold nanoparticles. Hybrids of phthalocyanines and gold nanoparticles can be subdivided according to the type of bonding: covalently bonded, formed due to coordination or electrostatic interactions.
Second, the introduction of substituents containing sulfur into the non-peripheral positions 3 and/or 6 of the phthalocyanine macrocycle promotes the bathochro-mic shift of the main absorption band (Q-band corresponding to the transition of an electron from HOMO to LUMO).[43]
Finally, the introduction of bulky substituents containing sulfur helps to reduce aggregation. This is especially important for the formation of thin films based on phthalo-cyanines from solutions.
7.1. Hybrids with gold nanoparticles: preparation and application
The synthesis of hybrid systems based on metal nanoparticles and phthalocyanines can significantly improve the characteristics of materials based on phthalocyanines.
Besides, the presence of phthalocyanines on the surface of nanoparticles leads to their stabilization.[96]
The authors of [18,27] carried out the functionalization of the surface of gold nanoparticles with benzylmercapto-and thiophenyl-substituted zinc phthalocyaninate (Figure 1). For this purpose, a solution of gold nanoparticles stabilized with tetraoctylammonium bromide was first prepared. The aqueous solution of gold chloride was stirred with a solution of tetraoctylammonium in toluene, and then NaBH4 was added. The stabilized nanoparticles were separated together with the organic phase. Then, solutions of nanoparticles and zinc phthalocyaninate were mixed. Molecules of thio-phenyl- and benzylmercapto-substituted phthalocyanines can interact with the surface of gold nanoparticles due to S-Au coordination bonds.
The formation of conjugates was confirmed by transmission electron and atomic force microscopy data. An increase in the size of nanoparticles in solution in the presence of zinc phthalocyanine was shown. The photochemical characteristics of arylmercapto-substituted zinc phthalocyanines were determined. It is shown that, due to the presence of residual bromine atoms on the surface of nanoparticles, the yield of singlet oxygen generation in hybrid nanoparticles is higher than that of the initial complex (BenzylS) 4Pc.
By the method of electrospinning, the authors of [27] succeeded in obtaining polymethyl methacrylate fibers with hybrid gold nanoparticles coated with a phthalocyanine shell. The resulting modified fibers efficiently generate singlet oxygen. They can potentially be used in antibacterial linen and ointments.
O.M. Bankole[68] modified the surface of alloys with the composition of Ag1Au3 and Ag3Au1 using zinc phthalocyaninate 24. The peripheral diaminopyrimidine groups of phthalocyanine form coordination bonds with the surface of nanoparticles. The resulting conjugates have improved nonlinear optical characteristics in comparison with complex 24. In this case, the highest value of the coef-
Figure 1. Surface modification of gold nanoparticles with benzyl mercapto-substituted zinc phthalocyaninate.[18,27]
Table 9. Photophysical characteristics for solutions in toluene of arylmercapto-substituted zinc phthalocyanines and corresponding hybrid gold nanoparticles.
Compound X, , nm abs' X , nm em' TF, ns
(PhenylS)4Pc[18] (PhenylS)4Pc+Au[18] (BenzylS)4Pc [27] (BenzylS)4Pc+Au [27] 692 685 710 699 702 698 725 708 0.15 0.09 0.03 <0.01 not presented not presented 0.33 0.54 2.60 ± 0.01 (1.00) 4.23 ± 0.07 (0.73) 1.74 ± 0.11 (0.27) 2.40 ± 0.01 (1.00) 0.88 ± 0.03 (0.74)a 2.17 ± 0.04 (0.26) a
a Abundances are given in brackets.
ficient of effective nonlinear absorption (peff) is observed for the conjugate with Ag^u nanoparticles.
Hybrid gold nanoparticles (AuNPs) coated with tetrasulfo-substituted aluminum phthalocyaninate (AlPcTS) molecules due to electrostatic interactions are presented in literature[24] (Figure 2). The surface of gold nanoparticles was preliminarily immobilized with a polyelectrolyte, and then a layer of sulfo-substituted aluminum phthalocya-nine was applied by the Layer-by-Layer method.
For the obtained hybrid material, a plasmon enhancement of fluorescence was observed, which can be used in biomarkers. An important role is played by the distance between phthalocyanine and the surface of nanoparticles. It has been shown that the best effect can be achieved at a distance of 7 polyelectrolyte layers.
Phthalocyanine complexes can get a sulfur-containing substituent due to the formation of conjugates with nanopar-ticles. N. Nwaji et al.[97] described a series of conjugates of nanoparticles (Au, Ag) and quantum dots (CdTeSe, CdTeSe/ZnO) with ball-type indium phthalocyaninate (Scheme 28).
Covalent bonding of the surface of nanoparticles and phthalocyanine 59 molecules was carried out through the amide bond between the carboxyl group of phthalo-cyanine and the amino group of glutathione molecules that is comprised of the shell of the nanoparticles. The reaction was carried out in the presence of 4-dimethylamino pyridine (DMAP) and DCC. The resulting conjugates have nonlinear optical properties and high quantum yields of the triplet state.
A similar approach to the synthesis of a conjugate of gold nanoparticles and an asymmetrically substituted complex 60 was used in the work by O.M. Bankole et al.[98] (Scheme 29).
The covalent bond was formed due to the interaction of the carboxyl groups of mercaptopropionic acid, which forms the shell of nanoparticles, and the amino group of complex 60. Carboxyl groups were preliminarily activated by interaction with N-hydroxysuccinimide in the presence of N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride.
Figure 3 shows a hybrid material formed due to cova-lent interactions between the surface of gold nanoparticles
Figure 2. Fluorescence microscopy (left) and schematic representation of gold nanoparticles modified with tetrasulfo-substituted aluminum phthalocyanine (right).[24]
and A3B type phthalocyanine containing a terminal thiol group.[36]
The resulting hybrid material is a promising pho-tosensitizer for photodynamic therapy, since it has a high quantum yield of the triplet state.
7.2. Near infrared absorption
The presence of absorption in the near IR range is necessary for the creation of photovoltaic cells,[99] the synthesis of photosensitizers for photodynamic therapy
O^HN*0
S>N^ NH-
G
M = InCI;
(1) X = CdTeSe/ZnO;
(2) X = CdTeSe;
(3) X = Ag;
(4) X = Au
Figure 3. Obtaining a hybrid by covalent bonding.[36]
of subcutaneous cancerous tumors,[100] in the preparation of catalysts for photooxidative processes,[101102] as well as the creation of IR labels.[103]
This section provides examples of the shift of the main absorption maximum of phthalocyanines (Q bands) to the near-IR region due to the presence of functional groups containing sulfur in non-peripheral positions of molecules (Table 9). In order not to take into account
the effect of the nature of the macrocycle on the position of the absorption maximum, only phthalocyanine complexes are considered here.
Due to the effective interaction between the phthalocyanine n-orbitals and the sulfur 3p orbitals, an increase in the total n-system of the complex is achieved. In this case, the absorption maximum of compounds substituted with functional groups containing sulfur shifts bathochromically. [42] For example, the absorption maximum of complex 21a is shifted by 20 nm bathochromically more than the unsub-stituted analogue.[39]
Using phenylthio- and benzylthio-substituted complexes as the examples, it was shown in [35] that the introduction of the substituents in the non-peripheral position (complexes 14a and 14b) promotes a bathochromic shift of the Q band relative to the peripherally substituted complexes 14c and 14d. The absorption maxima of octasubsti-tuted complexes 19 are shifted more bathochromically than tetrasubstituted 14. In this case, the absorption maximum of the Mn(III) complex is located most bathochromically.
N. Kobayashi et al.m described the synthesis of stable phosphorus(V) phthalocyanine 61a possessing absorption band beyond 1000 nm. Such a strong bathochromic shift is explained by the following factors:
- destabilization of HOMO due to electron-donor PhS groups in non-peripheral positions of the phthalocya-nine macrocycle;
- deformation of the phthalocyanine macrocycle relative to the plane due to the steric effect of substituents;
- stabilization of both LUMO and HOMO due to the electron-withdrawing central phosphorus atom in a high oxidation state.
The largest bathochromic shift of the Q band was achieved only when functional groups containing another representative of chalcogenides, Se.[43]
Y. Zorlu et al. showed the correlation between the distortion of phthalocyanine macrocycle by bulky substituents and the position of the Q band maximum. Two complexes 62a and 62b with alkylthio groups in nonperipheral positions were obtained. The presence of bulky tert-butyl groups resulted in hypsochromic shift of Q band maximum for complex 62b in comparison with hexyl-substituted compound 62a.
Phthalocyanines and Naphthalocyanines with Sulfur-Containing Functional Groups Table 9.
Compound R1 R2 R3 R4 M Q band Reference
14a PhS H H H TiO 747b [35]
14c H PhS H H TiO 714b [35]
14b PhCH2S H H H TiO 746b [35]
14d H PhCH2S H H TiO 714b [35]
19b C5H11S H H C5H11S Mn(OAc) 893b [64]
19c C5H11S H H C5H11S TiO 808b [64]
19a C5H11S H H C5H11S VO 850b [63]
21a H C6H13S C6H13S H TiO 736b [39]
61a PhS H H PhS P(OMe)2a 1018c [43]
61b PhSe H H PhSe P(OMe)2a 1033c [43]
62a C6H13S H H C6H13S HH 810c [104]
62b tBuS H H tBuS HH 755c [104]
a - the complex with a positive charge, counterion - [PF6]-. b - CH2Cl2 used as a solvent. c - CHCl, used as a solvent.
7.3. Gas sensors
Dinaphthalocyanine complexes of a sandwich structure can be easily and reversibly oxidized due to the presence of an extended n-system, as well as a n-radical nature. This peculiarity allowed Y. Chen et al. to create a NO2 sensor based on them (Figure 4).[105]
It was noted that the synthesis of the complexes was carried out by analogy with the method.[87] However, the detailed synthesis and yields of the target compounds are not given. Thin films were prepared by the Langmuir-Blodgett method and then treated with nitric oxide vapor. The process was monitored spectrophotometrically. A reversible change like the spectrum under the action of an oxidizing agent (NO2) is shown.
For tetranuclear complex 56, the sensitivity to volatile organic compounds (chloroform, acetone, CCl4, methanol, ethanol) was studied. The current is shown to be increased by several times during the interaction of a thin film of phthalocyanine and vapors of the analyzed com-pounds.[89]
7.4. Photovoltaic cells
M. Mayukh et al.[99] described photovoltaic cells based on titanium phthalocyaninates substituted with alkylthio
groups at the periphery of the macrocycle (complexes 21a, 21d, 21e, Table 6) - an electron donor with p-type semiconducting properties and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate - an electron acceptor with «-type semiconductor properties. Phenyl-C61-butyric acid methyl ester was used as an additional electron acceptor. The function of the electrodes was performed by a layer of In2O3: Sn (anode) and Al (cathode). LiF was used as an additive to improve ion transport.
Due to the central titanium ion and peripheral groups containing sulfur in the film obtained by the spin-coating method, these complexes absorb at a wavelength of about 900 nm. The authors[99] succeeded in obtaining a material with a bulk heterojunction with a sufficiently high (0.71 V) value of the open circuit potential (Figure 5).
Conclusions
This review considers the main methods for the synthesis of phthalocyanines and 2,3-naphthalocyanines bearing sulfur-containing functional groups. Both approaches based on substituted nitriles and methods for modifying functional groups in the formed phthalocyanine macrocycle are presented. Compounds of both planar and sandwich structures are considered.
Figure 4. Structures of the Ln complexes (a) and their UV-Vis spectra (b): dash-dotted line - thin film of dinaphthalocyanine Gd; dotted line - after NO2 oxidation; solid line - 2 days after oxidation (adopted from [105]).
Figure 5. Titanium phthalocyaninate structure, scheme of the photovoltaic cell and absorption spectra of titanium phthalocyanine in solution (black line), thin film (red line) and absorbed photon to current efficiency (APCE) (blue line) (adopted from [99]).
According to the methods for the synthesis of phthalo-cyanines and 2,3-naphthalocyanines substituted with functional groups containing sulfur, the following conclusions can be drawn:
- the most accessible, in synthetic terms, are alkyl-thio- and arylthio-substituted compounds.
- the main disadvantage of thiol-terminated phthalo-cyanines is the tendency to form compounds with disulfide bonds as by-products.[73]
- the least amount of by-products and, accordingly, the ease of isolation is characteristic of symmetrically substituted complexes.
- in the case of unsymmetrically substituted phthalo-cyanines of the A3B type, the yields at the stage of statistical condensation are rather low.[36]
Noteworthy are those phthalocyanines, which form coordination bonds with the surface of nanoparticles, which are promising for the creation of hybrid materials with gold nanoparticles. Their preparation is less laborious than in the case of hybrids with covalent bonds.
The introduction of functional groups containing sulfur into non-peripheral positions 3 and 6 of the phthalocyanine
macrocycle promotes the bathochromic shift of the Q band to the near-IR region up to 1018 nm.[43]
For other applications, the most widely used compounds are those containing long-chain alkylthio groups. These compounds are readily available and have good solubility. On their basis, homogeneous thin films can be easily obtained by the Langmuir-Blodgett and spin-coating methods. This makes these compounds promising for the creation of photovoltaic cells and gas sensors.
Acknowledgements. This work was supported by a grant RSF No. 19-73-00099.
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Received 18.02.2021 Accepted 12.03.2021
