Morphology dependence of excitonic energy transfer in light- harvesting dendrimers having benzyl ether-type peripheries

Morphology dependence of excitonic energy transfer in light‐harvesting dendrimers (4thm Q: m = 1, 3, and 4) with fourth branching generation is investigated from the measurements of photoluminescence (PL) spectra and the 1H‐NMR spin‐spin relaxation time (T 2). In these dendrimers, intense PL bands from the core appear for the photo‐excitation at the light‐harvesting peripheries due to the highly efficient excitonic energy transfer from the peripheries to the core. However, with the increase in the number of periphery‐subunits m, the quantum efficiency of the excitonic energy‐transfer becomes lower, and the T 2 of the exterior methoxy‐groups in the outer peripheries becomes short. These results suggest that the congestion among the aromatic rings in the outer peripheries increases anharmonicity of torsional vibrations in the peripheries, and the exciton transfer from the peripheries is strongly disturbed by dissipation processes due to the anharmonicity of the torsional vibration. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)