SOLID-STATE SPECTRA OF TITANYLPHTHALOCYANINE AS VIEWED FROM MOLECULARDISTORTION

The title compound (TiOPc) is a well-known, near-IR-active photoconduc tor used practically for GaAsAl laser printers. The influence of inter molecular interactions on the optical absorption has been investigated in single crystals (phases I and II) and evaporated films (amorphous phase, phases I, II, and Y) from the standpoint of molecular distortio n and interplanar pi-pi interactions. Careful reexamination of the X-r ay structure analysis revealed that the TiOPc molecules are considerab ly distorted in phase II (near-IR-active) and there are close pi-pi at omic contacts along the molecular stack. This molecular distortion (re duction in molecular symmetry: C-4v - C-1) lifts the doubly degenerate excited state, giving rise to the two absorption bands (660 and 840 n m) whose transition moments are orthogonal. The major part of the opti cal absorption spectra in phases I and II can be interpreted in terms of the distortion of molecular framework. Furthermore, the molecular d istortion is found to be closely linked with interplanar pi-pi atomic contacts, as supported by the temperature dependence of absorption spe ctra and lattice contraction. The correlation between molecular distor tion and pi-pi interactions via pi-pi atomic contacts suggests that th e molecule can presumably be distorted in the solid state due to pi-pi interactions along the molecular stack.