Temperature dependence of excitation energy transport in a benzene branching molecular system

The dynamics of excitation energy transport in a benzene centered branched molecule are presented. This system contains pyridine distrylbenzene (pyridine-DSB) chromophores attached to the benzene center giving the 1,3,5-tris((E)-2-{4-[(E)-2-pyridin-4-ylvinyl]phenyl}vinyl)-2,4,6-trimethylbenzene (T155) multi-chromophore system. Excitation energy transport was investigated by ultra-fast time resolved fluorescence anisotropy measurements. A depolarization time of ∼800 fs was observed at room temperature and the anisotropy decay time increased at lower temperatures while a new fast decay component appeared. The anisotropy decay residual value was found to decrease systematically with decreasing temperature. From consideration of both steady-state and time-resolved results it is found that the benzene branching center has excitations localized on pyridine-DSB chromophores at room temperature. The appearance of fast anisotropy decay component in addition to slow (∼1 ps) component at low temperature suggests that energy transfer dynamics approaches the intermediate (crossover) characteristics of incoherent and coherent regimes.