Department of Chemistry, LMU University of Munich, Butenandtstrasse 13, 81377 Munich, Germany.
J Am Chem Soc. 2010 Dec 1;132(47):16777-82. doi: 10.1021/ja101544x. Epub 2010 Nov 5.
We investigate the ultrafast resonant energy transfer of a perylene bisimide dyad by pump-probe spectroscopy, chemical variation, and calculations. This dyad undergoes transfer with near-unit quantum efficiency, although the transition dipole moments of the donor and acceptor are in a perfectly orthogonal arrangement to each other in the equilibrium geometry. According to the point dipole approximation used in Förster theory, no energy transfer should occur. Experimentally we do, however, find an ultrafast transfer time of 9.4 ps. With the transition density cube approach we show that in the orthogonal arrangement the Coulombic interactions do not contribute to the electronic coupling. Through the change of the spacer in both length and chemical character, we can clearly exclude any Dexter-type energy transfer. The temperature effects on the Förster resonant energy transfer rate demonstrate that energy transfer is enabled through low-frequency ground-state vibrations, which break the orthogonal arrangement of the transition dipole moments. The dyads presented here therefore are a first example that shows with extreme clarity the decisive role vibrational motion plays in energy transfer processes.
我们通过泵浦探针光谱、化学变化和计算研究了苝二酰亚胺二聚体的超快共振能量转移。尽管供体和受体的跃迁偶极子在平衡几何形状中彼此完全正交排列，但该二聚体仍以近乎单位的量子效率进行转移。根据福斯特理论中使用的点偶极近似，不应发生能量转移。然而，实验中我们确实发现了 9.4 ps 的超快转移时间。通过跃迁密度张量方法，我们表明在正交排列中，库仑相互作用不会对电子耦合产生贡献。通过改变间隔物的长度和化学性质，我们可以清楚地排除任何 Dexter 型能量转移。对福斯特共振能量转移速率的温度效应表明，能量转移是通过低频基态振动实现的，这种振动打破了跃迁偶极子的正交排列。因此，这里呈现的二聚体首次非常清楚地表明，振动运动在能量转移过程中起着决定性的作用。
