Highly ordered thin films of octasubstituted phthalocyanines

Phthalocyanines (Pc) modified at eight positions with benzyloxyethoxy groups (CuPc(OC(2)OBz)(8) and H2Pc(OC(2)OBz)(8)) form discotic mesophases in the bulk and self-assemble into cofacial rodlike aggregates in monolayers. These Pc aggregates form close packed arrays which are simple to process into highly coherent multilayer thin films. When these self-organizing molecular systems are compressed on the surface of an LB trough, the Pc columns align parallel to the compression barriers and form a rigid bilayer film (ca. 5.6 nm thick). Sections of these bilayer films can be mechanically removed from the trough surface with complete retention of integrity of the remaining film. This unprecedented behavior appears to arise from the multiple pi-pi interactions between adjacent Pcs, resulting in unusually strong noncovalent interactions. AFM and STM studies of monolayer and bilayer films show that they consist of Pc columns which are coherent over distances of 50-100 nm. Thin films consisting of up to 15 bilayers (ca. 84 nm) can be quickly built by a "mechanical stamping" process, and small-angle X-ray scattering characterization of these film materials confirms their unusual coherence. Large electrical and optical anisotropies are observed in multilayer films of CuPc(OC(2)OBz)(8) and H2Pc(OC(2)OBz)(8) which are comparable to those previously reported for thin film assemblies based on side-chain-modified silicon phthalocyanine polymers.