Peripherally substituted phthalocyanines

Scheme 2 Synthesis of peripherally substituted phthalocyanines. DMSO = dimethylsulfoxide...

Thus, several types of substituent have been utilized for the uniformly peripherally substituted phthalocyanines. Overall, oxo and thioether links, as well as ester groups, provided ordered mesophases, in contrast to alkyl, alkoxy-methyl, and poly(ethyleneoxide) chains. The melting transition temperatures increased in the order ethyleneoxide < alkylthio < alkoxymethyl... 

A phthalocyanine macrocycle has a tendency to organize itself and forms stacks in which there is interaction between the large 7r-system of the adjacent rings in such a way to give low-dimensional compounds. In the pure form phthalocyanines have an intrinsic band gap of 2 eV [3] and hence are insulators with low conductivities. For example, unsubstituted phthalocyanine monomers [3] and peripherally substituted phthalocyanines [76] exhibit room-temperature conducitivity lower than 10 S cm for air-equilibrated samples. They attain the required molecular stacking for effective n—n interaction and hence exhibit large conductivities when excess electrons or holes are introduced into the conduction or valence bands. This is normally carried out by chemical or electrochemical doping [77-79]. 

Cook and coworkers [216] have synthesized a range of unsynunetrical, non-peripherally substituted phthalocyanines 49. Their mesophase behaviour (Table 53) is extremely sensitive to the degree of asymmetry (substituents) in these non-peripherally substituted systems. Mesophase behaviour is destroyed if the diester 50 is saponified to give the diacid (R2=R3= CH2CH2CH2CO2H). Similarly, substitution of an additional alkyl group in the penta-al-kyl mono-3-hydroxypropylphthalocyanines leads to materials (R2 = R3 = (CH2)30H) that give only monotropic mesophases [217, 221]. 

The alkali metal dicyano(phthalocyaninato)cobalt-(III) complexes M [PcM(CN)2] were characterized by infrared spectroscopy and in the case of peripherally substituted phthalocyanines also by UV-vis and H NMR spectroscopy. The H NMR spectra of the complexes recorded in acetone-c/ft show the expected number and intensities of signals that confirm the proposed structures. The fact that H NMR spectra are obtained supports the proposed oxidation state -1- 3 and the octahedral ligand field of the Co atom. Otherwise a paramagnetic substance would result. 

Palladiumphthalocyanine (PcPd) can be synthesized from phthalimide, ammonium molyb-date(VI), urea and palladium(II) chloride in nitrobenzene.285 Peripherally substituted palladium phthalocyanine is prepared by the reaction of phthalonitrile286 or isoindolinediimine114,117 and palladium(II) acetate in 2-(dimethylamino)ethanol. Also a metal insertion into metal-free phthalocyanine in dimethylfonnamide starting from bis(triphenylphos-phane)palladium(II) chloride has been performed.141,287... 

A peripheral substitution of phthalocyanines can be achieved via exchange of halogen atoms in halogenated phthalocyanines with alkali alkoxide340 or thiolate341. 

Ganivet, C.R., Ballesteros, B., de la Torre, G., Clemente Juan, J.M., Coronado, E. and Torres, T. (2012) Influence of peripheral substitution on the magnetic behaviour of single-ion magnets based on homo- and heterolep-tic TbIII Bis(phthalocyaninate). Chem. Eur. J., 19, 1457-1465. 

Abstract In this chapter, recent progress in the synthesis, crystal structures and physical properties of monomeric phthalocyanines (Pcs) is summarized and analysed. The strategies for synthesis and modification of Pcs include axial coordination of central metal ions, peripheral substitution of Pc rings and the ionization of Pcs. The crystal structures of various typical Pcs, especially the effects of different synthetic and modification strategies on the supramolecular assemblies of Pcs via %—% interactions between Pc rings, are discussed in detail. Finally, the UV-vis spectroscopic, conducting, magnetic and catalytic properties of some Pcs with crystal structures are presented briefly, and the correlations between various properties and the molecular structure discussed. 

The near IR spectra of the tetrakis(cumylphenoxy)phthalocyanines have not been reported before. The absorption in the Cu complex and one of the absorptions in the Co complex lie close to bands which have been tentatively assigned to trip-multiplet transitions in other phthalocyanines.(14) However, the other absorption bands shown in Table 1 have not been previously reported for phthalocyanines with no peripheral substitution. The small absorption cross sections of these bands in the cumylphenoxy phthalocyanines suggest that they are forbidden transitions. Possible assignments for these bands include a symmetry forbidden electronic transition (like the MLCT transitions in NiPc discussed above) becoming vibronically allowed, d-d transitions on the metal ion, or trip-multiplet transitions. Spectroscopic studies are in progress to provide a more definitive assignment of these absorptions. 

Comparison of the peripherally and nonperipherally substituted tetra amino phthalocyanine complexes of Mn( (OH)MnPc (NI I2)4 with (OH)MnPc (NH2)4), shows that the nonperipherally substituted derivatives are slightly more difficult to reduce (considering second reductions), Table 2 [44,45], Substitution at the nonperipheral position, using electron donating substituents, results in greater enhancement of electron density compared to peripheral substitution, and hence should result in ease of oxidation, and more difficult reduction as shown in some cases Table 2. 

Kobayashi N, Ogata H, Nonaka N, Luk yanets EA (2003) Effect of peripheral substitution on the electronic absorption and fluorescence spectra of metal-free and zinc phthalocyanines. Chem Eur J 9(20) 5123-5134... 

Figure 4 shows the molecular structures of the monomeric phthalocyanines used as the active layer of p-type OFET devices, and Table 1 organizes the performance of these phthalocyanine-based OFETs. As can be seen, unsubstituted metal-free phthalocyanine and its metal complexes, axial substituted metal phthalocyaines, and peripheral tetra-substituted phthalocyanines all can work as p-type semiconductors for OFET devices. Most of the semiconductors composed of peripheral unsubstituted and axial substituted phthalocyanine derivatives are prepared through vacuum deposition method with a few exceptions being made of corresponding single... 

The majority of the early experiments were carried out on a variety of alkoxy-substituted phthalocyanines on the basis of which the following qualitative conclusions could be drawn (a) the intra-columnar mobility was relatively insensitive to the nature of the peripheral alkyl chain substituents which did however influence the mesomorphic properties (b) the mobility invariably decreased on... 

Warman JM, de Haas MP, van der Pol JF, Drenth W. (1989) Charge separation and recombination in pulse-irradiated columnar aggregates of peripherally octa- -alkoxy-substituted phthalocyanines. Chem Phys Lett 164 581-586. 

In this chapter we report on some novel strategies that have been pursued to obtain efficient second-order nonlinear molecules starting from the well-known phthalocyanines. In principle, these planar centrosymmetric molecules do not present second-order activity and have been extensively studied for third-order applications. In order to induce asymmetry, two main approaches have been followed a) peripheral substitution of the macrocycle with donor and acceptor groups and b) structural modifications of the Pc core to reduce the symmetry, the resulting-noncentrosymmetric compounds (i.e. subphthalocyanines) presenting variable degrees of dipolarity/octupolarity in the nonlinear response. 

However, the area was further studied by Usol tseva [205] who synthesized several peripherally carboxylated phthalocyanines and successfully characterized their phase behaviour as lyotropic columnar. The complexes in Figure 111 with M = 2H, Cu, Zn or Co(II) and X = H, Y = COOH and Z H or COOH were found to show columnar nematic and hexagonal phases in aqueous ammonia, but this was suppressed when the phthalocyanine ring was substituted according to X = COOH and Y = Z = H or when the central metal ion was Al(III). In this latter case, suppression of the mesomorphism was due to the formation of p-oxo dimers ([PcAl-O-AlPc]). 

J.M. Warman, M.P. de Haas, J.F. van der Pol, and W. Drenth, Charge Separation and Recombination in Pulse Irradiated Columnar Aggregates of Peripherally Octa-n-alkoxy-Substituted Phthalocyanines, Chem. Phys. Lett., 164 (1989) 581. 

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