Quenching of energy transfer by freezing molecular vibrations in light-harvesting small dendrimer

Temperature dependence of the energy-transfer dynamics in a light-harvesting small dendrimer (star-shaped stilbenoid phthalocyanine: SSS1Pc) having oligo (p-phenylenevinylene) peripheries is investigated. We measured stationary and time-resolved photoluminescence (PL) spectra of SSS1Pc under the selective excitation of the periphery in SSS1Pc. At higher temperatures than the freezing point of the solvent, highly efficient energy transfer from the peripheries to the core in SSS1Pc gives rise to an intense core-PL band of SSS1Pc. However, with cooling down below the freezing point temperature, the core-PL is obviously quenched in spite of less temperature dependence of the decay time constant of the core-PL. This temperature dependence clearly indicates that dynamical processes mediated by molecular vibrations play an important role in the energy transfer from the periphery to the core in SSS1Pc.