TY - JOUR
T1 - Hopping versus Tunneling Mechanism for Long-Range Electron Transfer in Porphyrin Oligomer Bridged Donor–Acceptor Systems
AU - Gatty, Melina
AU - Kahnt, Axel
AU - Esdaile, Louisa
AU - Hutin, Marie
AU - Anderson, Harry
AU - Albinsson, Bo
PY - 2015/6/18
Y1 - 2015/6/18
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84935013890&partnerID=8YFLogxK
U2 - 10.1021/jp5115064
DO - 10.1021/jp5115064
M3 - Article
SN - 1520-6106
VL - 119
SP - 7598
EP - 7611
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 24
ER -