Phenylen-basedデンドリマーにおけるπ*共役を介する高速エネルギー伝達と分子振動解析

概要

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At room temperature, a rapid energy transfer (ET) occurs efficiently under the selective excitation of light-harvesting (LH) antennas in phenylene-based dendrimers (PhDGn;n=1,2). However, the ET quantum efficiency degrades obviously at temperatures lower than 〜100K. And as well as that, rising of the ET is very fast. The rapid rising of the ET can not be explained by a Forster mechanism. The PhDGn dendrimers have the LH antennas with meta-linked branching architecture. In the ground state, π-conjugations inside antennas and between antennas and core are not sufficient because of the low coplanarity between them. To realize such rapid ET process, a conjugation network of excited states is essential for highly efficient ET. In the excited states, this π*-conjugation network is expected to be characterized by a steric hindrance and torsional vibrations of aromatic rings in LH antennas. For understanding the rapid ET and its temperature dependence in PhDGn dendrimers, we analyzed torsional vibration in model molecules for LH antenna subunits by a semiempirical molecular orbital calculation, and found that the rapid ET processes through π*-conjugation network take place with thermal excitation of torsional vibrations.
2010-03-00