1990 Volume 47 Issue 10 Pages 809-815
Transient infrared absorption spectra and decay dynamics of triplet excitons (T1 excitons) of metal-free phthalocyanine (H2Pc) fine particles in their α, τ, and β modifications have been investigated with a newly constructed microsecond time-resolved infrared spectrometer. Observed decay curves are explainable only as superpositions of the first and second order terms, indicating that T1 excitons relax through unimolecular (intersystem crossing) and bimolecular (T-T annihilation) processes. In the α form, the observed lifetime was mardkedly shorter than those in the τ and β forms. This suggests that, in the α form, T1 excitons have a large diffusion length which accelerates the relaxation through the T-T annihilation path. Diffusion of T1 excitons occurs through an electron exchange between adjacent molecules. Thus, the present results show the feasibility of the intermolecular electron hopping in the a form. Observed differences of electron mobilities in these polymorphic forms are discussed in relation to their crystal structures (particularly overlapping of π electrons between stacked H2Pc macrorings) and dark conductivities.
