Electronic states and relaxation dynamics of silicon phthalocyanine dimers

Absorption and emission spectra of monomers and dimers of [tetramethoxytetrakis(octyloxy)phthalocyaminato]-silicon have been measured as a function of solvent and concentration, In contrast to the monomer, the fluorescence of the dimer is shifted to lower energy by about 4000 cm(-1), and the emission quantum yield is reduced by a actor of 10(-3). The spectroscopic data are analyzed in the strong coupling limit of dimer models and lead to an excitation exchange interaction term of 1770 cm(-1) and an evaluation of the excited state lifetime of ca. 24 ps. This fast decay is dominated by nonradiative processes. The admixture of ion pair configurations is suggested to provide an efficient coupling to the environment and channel of decay of the exited state energy. Small contributions of such configurations to the,ground state are also invoked to explain the marked changes in the absorption spectra as a function of environment (solvent) and concentration (aggregation).