Dye Sensitization with Octasubstituted Liquid Crystalline Phthalocyanines

New liquid crystalline octaamide (C₁₂) and octaester (C₁₂) copper phthalocyanines (LC-Pc), which form self-assembled structures in solutions and in cast films, act as effective sensitizers for the photoelectrochemical response of the layered semiconductors, n-SnS₂. The photocurrent yield spectra of these cast films, at a wide range of coverages, show a single sharp Q-band at a position corresponding to close packed monolayer assemblies of flat-lying Pc's. Quantum yields per absorbed photon are high (QYAP ≈ 44%) for the close packed monolayers. In contrast, films from a short-chain substituted and an unsubstituted CuPc on SnS₂ show Q-band photocurrent yield spectra due to both the monomer and H-aggregate forms. These phenomena suggest that the efficiency of exciten transport through a self-assembled LC-Pc film strongly depends on the separation distance between the chromophores. The interfacial structure of the mesogenic molecules at the semiconductor or metal surface appears to be critical in determining the overall exciton transport efficiency in columnar mesophases.