Hopping versus Tunneling Mechanism for Long-Range Electron Transfer in Porphyrin Oligomer Bridged Donor–Acceptor Systems
| Autor: | Harry L. Anderson, Louisa J. Esdaile, Bo Albinsson, Axel Kahnt, Melina Gilbert Gatty, Marie Hutin |
|---|---|
| Rok vydání: | 2015 |
| Předmět: | |
| Zdroj: | The Journal of Physical Chemistry B. 119:7598-7611 |
| ISSN: | 1520-5207 1520-6106 |
| Popis: | Achieving long-range charge transport in molecular systems is interesting to foresee applications of molecules in practical devices. However, designing molecular systems with pre-defined wire-like properties remains difficult due to the lack of understanding of the mechanism for charge transfer. Here we investigate a series of porphyrin oligomer-bridged donor-acceptor systems Fc-Pn-C60 (n = 1-4, 6). In these triads, excitation of the porphyrin-based bridge generates the fully charge-separated state, Fc(•+)-Pn-C60(•-), through a sequence of electron transfer steps. Temperature dependence of both charge separation (Fc-Pn*-C60 → Fc-Pn(•+)-C60(•-)) and recombination (Fc(•+)-Pn-C60(•-) → Fc-Pn-C60) processes was probed by time-resolved fluorescence and femtosecond transient absorption. In the long triads, two mechanisms contribute to recombination of Fc(•+)-Pn-C60(•-) to the ground state. At high temperatures (≥280 K), recombination via tunneling dominates for the entire series. At low temperatures (280 K), unusual crossover from tunneling to hopping occurs in long triads. This crossover is rationalized by the increased lifetimes of Fc(•+)-Pn-C60(•-), hence the higher probability of reforming Fc-Pn(•+)-C60(•-) during recombination. We demonstrate that at 300 K, the weak distance dependence for charge transfer (β = 0.028 Å(-1)) relies on tunneling rather than hopping. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|