MOLECULAR DISTORTION AND PI-PI INTERACTIONS IN THE SOLID-STATE OF TITANYLPHTHALOCYANINE

The influence of intermolecular interactions on the optical absorption has been investigated in single crystals (phases I and II) and evapor ated films (amorphous phase, phases I, II and Y) from the standpoint o f molecular distortion and interplanar pi-pi interactions. Careful re- examination of the X-ray structure analysis revealed that the TiOPc mo lecules are considerably distorted in phase II (near-IR active) and th ere are close atomic contacts along the molecular stack. This molecula r distortion (reduction in molecular symmetry: C-4v-->C-1) lifts the d oubly degenerate excited state, giving rise to the two absorption band s (660 and 840 nm) whose transition moments are orthogonal. The major part of the optical absorption spectra in phases I and II can be inter preted in terms of the distortion of molecular framework. Furthermore, the molecular distortion is found to be closely linked with interplan ar pi-pi interactions, as supported by the temperature dependence of a bsorption spectra and lattice contraction. The correlation between mol ecular distortion and pi-pi interactions suggests that the molecule ca n be distorted in the solid state due to pi-pi interactions along the molecular stack.