Steady-state and time-resolved photophysical studies on a series of gallium phthalocyanine monomers and dimers

Intramolecular interaction between coplanar-stacked phthalocyanine (Pc) and porphyrin molecules plays an important role in the energy- and electron-transfer process. A series of results from different photophysical experiments on gallium phthalocyanine compounds are initially described. The PcGa dimer with a direct gallium-gallium bond, i.e. [tBu₄PcGa] ₂·2dioxane, may exist in two different conformations: one in which the two phthalocyanines are poorly interacting and the other in which they are very close and strongly interacting. In the former, the emission lifetime is quite close to that of the monomer model compounds; in the latter, it is much shorter probably due to different radiative and nonradiative deactivation constants from those of the monomers. Because no significant difference between the absorption spectra of the monomer and dimer was observed in the photophysical experiments, implying that no ground-state interaction can be assessed, the results regarding triplet excited state lifetimes of [tBu ₄PcGa]₂·2dioxane can be attributed to strong intramolecular interactions existing only in the excited state.