Depression of excitonic energy transfer by freezing molecular vibrations in meta -linked branching dendrimers

The temperature dependence of excitonic energy transfer is investigated in both small and large dendrimers having meta ‐linked light‐harvesting peripheries. In these dendrimers, highly efficient excitonic energy transfer takes place from peripheries to core at room temperature and gives rise to intense core photoluminescence (PL) upon selective excitation of the peripheries. Upon direct photo‐excitation of the core chromophore, the intensity of core‐PL increases monotonically with decreasing temperature. However, during selective excitation of the peripheries, the enhancement of the core‐PL is markedly suppressed at temperatures lower than 100 K in both dendrimers. This result demonstrates that torsional vibrations of adjoining aromatic rings in the peripheries mediate excitonic energy transfer, and that the freezing of such vibrations at low temperature strongly inhibits the transfer in these meta ‐linked dendrimers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)