Publication

Bimolecular excited-state electron transfer with surprisingly long-lived radical ions

Bimolecular excited-state electron transfer with surprisingly long-lived radical ions
A. A. Alsam, S. M. Aly, A. Usman, M. R. Parida, S. del-Gobbo, E. Alarousu, and O. F. Mohammed
J. Phys. Chem. C, 119(38), pp 21896-21903, (2015)​
A. A. Alsam, S. M. Aly, A. Usman, M. R. Parida, S. del-Gobbo, E. Alarousu, and O. F. Mohammed
Bimolecular electron transfer
2015
We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3’-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steady-state and time-resolved techniques, including femto- and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN+• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived ( 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor−acceptor system with potential applications in organic solar cells.


 
DOI: 10.1021/acs.jpcc.5b06636