Stacked Phthalocyanine Polymers

Phthalocyanine complexes of Ge were prepared by Marks et al. and converted to stacked polymers imder dehydrative conditions. The degree of polymerization for 

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A more fruitful approach has been to make stacked phthalocyanine polymers with oxygen bridges between the metals. Dehydration of phthalocyanine complexes of Si, Ge and Sn produces a face-to-face oxygen bridged stacking pattern shown in Scheme Since electrical, optical and magnetic properties of... 

Figure 17.4. General stmcture of cofacially stacked phthalocyanine polymers.

Stacked phthalocyanine polymers (52) with oxygen bridges between the metal atoms have been prepared by dehydration of the phthalocyanine complexes of Si, Ge, and Sn to produce face-to-face stacking polymers." " When the oxygen-bridged systems are oxidatively doped, they become electrically conducting or semiconducting. 

Figure 17.5. General structure of cofacially stacked substituted phthalocyanines polymers.

Like monomeric phthalocyanines, polymeric phtha-locyanines also show improvements in electrical conductivity on doping with iodine [125-136]. In the latter case, however, the improvement in electrical conductivity is only two or three orders of magnitude compared to monomeric phthalocyanines, which show improvements in conductivity by eight to ten orders of magnitude [80]. The electrical conductivity of doped phthalocyanine polymer depends on the nature of donor and acceptor units and their orientation and their repeat distance. The nature of stacking and the presence of crosslinked structures introduce randomness in the overlap of orbitals, thereby causing interruption of... 

Cofacial phthalocyanine polymers are materials in which file macrocyclic rings are stacked in a shish-kebab maimer with the metals as part of file polymeric chain. " These polymers often display excellent thermal and chemical stability and are electrically conducting, sometimes even in the absence of a doping agent. Scheme 9 shows the synthesis of polymer 41 by reaction of the ferrous phthalocyanine complex (39) with pyrazine (40). ... 

Characterization of conjugated metallopolymers can be difficult. When the metals are paramagnetic, very broad NMR spectra are obtained. Also, many metal complexes, particularly porphyrins and phthalocyanines, aggregate in solution. This leads to broad NMR spectra and can lower solubility. Some researchers have used bulky substituents to disrupt cofacial stacking, but this can add several synthetic steps to the polymer preparation. It is often difficult to obtain clear, unequivocal characterization of the structures of metallopolymers. 

The cofacially stacked polymeric phthalocyanines can exhibit high electrical conductivities in either the undoped or the doped state (Table 7-1) [166,168,170]. For comparison, low molecular weight phthalocyanines MPc or naphthalocyanines MNc (M = Fe, Cu, Co, Ni, Zn) exhibit values between a = 10 and 10 S cm V For undoped polymers. Table 7-1 shows that polymerization through cyano- and tetrazine-bridging is particularly effective in increasing the conductivity. This effect can be ascribed to the existence of additional interactions (Ti-orbital interactions through the bonds) [170,194]. 

Fig. 3 Different ways of assembling phthalocyanines (a) a ladder polymer (b) a plane polymer (c) and (d) stacked arrangements...

Phthalocyanine-based polymers with shish-kebab type n -stacked structures, 7.47, are generally prepared by two different routes. These are illustrated in Scheme 7.7, where L is typically a pyrazole, diisocyanide, or p-bipyridine, and a wide variety of metals (e.g. Fe, Ru, Os) and non-metals (e. g. Si, Ge) have been used. The... 

Another interesting material consists of the doped forms of covalently linked siloxane-phtha-locyanine (Pc) complexes, [Si(Pc)0]n. In these polymers, the planar phthalocyanine units are apparently stacked face-to-face and form columns, due to the silicon-oxygen-silicon bonds. The polymers appear to be intrinsically metallic systems. The principal pathways of conductivity are perpendicular to the phthalocyanine planes. The extended n-n systems that form result from face-to-face overlaps of the phthalocyanine units. This enables the electrons or holes to travel in a perpendicular direction. 

Recently, Wynne and co-workers [1,2] and Marks and co-workers [3-6] described the synthesis and characterization of inorganic-organic polymers, in which a metallic or pseudometallic element alternates with a linear-chain bridging atom, like oxygen or fluorine. The metallic or pseudometallic element is usually the centr atom of a phthalocyanine system, and the bridge-stacked polymeric structure is rigid. These derivatives are electrical conductors after iodine oxidation. 

The presence of flexible side-chains make them soluble in common organic solvents [98,204-7]. These polymers have been proved by solid-state NMR and small-angle X-ray diffraction measurements to have hexagonal columnar structures in which the phthalocyanine cores are horizontally stacked with respect to the columnar axis, even at ambient temperatures [107,139,207]. The rigid rod nature of these polymers have been proved experimentally [207,208]. Their completely hydrophobic polymer allows for the controlled and highly reproducible deposition of ultra-thin films. LB films are used as branes in field effect transistors (PET S) and chemical sensors [209]. Devices based on the LB films show stable electroactivity and the electrodes show an almost Nemstian response. The change of pH in the electrolyte does not show any long time drifts. 

The thermal polycondensation of dihydroxy(metallo)phthalocyanines to cofacially stacked polymer in the solid state as example of a type III polymers [equation (7)] is topotactic and under topochemical control, which means that well-defined intermolecular distances and interactions in the lattice control the reaction [56]. Following a kinetic study the fraction of unreacted -OH end groups X over time does not obey a first order kinetics (X = exp(— 2 ), M = Si, Ge, Sn n = 50-200). 

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