Long-range electron transfer across a π -conjugated chain: Role of electron correlations

We consider a prototype polyene chain donor-π(bridge)-acceptor. The distance between the donor and the acceptor is varied by increasing the number of atoms in the bridge and the rate of electron transfer kET is studied for a series of different donors D=NH₂,0.2em0exOCH₃,0.2em0exSCH₃, and a fixed acceptor A=NO₂. We observe a large kET even at a D-A separation of ~450.3em0ex, unexpected from the standard noninteracting theories. Such a long-range electron transfer is primarily due to the formation of bound electron-hole pair (exciton) across the donor-bridge-acceptor atoms. Calculations at various levels, semi-empirical (with inclusion of configuration interactions) and many-body models (using density matrix renormalization group theory), have been performed to accurately account for such electron correlations.