Challenges in distinguishing superexchange and hopping mechanisms of intramolecular charge transfer through fluorene oligomers

Randall H Goldsmith; Orlando DeLeon; Thea M Wilson; Daniel Finkelstein-Shapiro; Mark A Ratner; Michael R Wasielewski

doi:10.1021/jp801084v

Challenges in distinguishing superexchange and hopping mechanisms of intramolecular charge transfer through fluorene oligomers

J Phys Chem A. 2008 May 15;112(19):4410-4. doi: 10.1021/jp801084v. Epub 2008 Apr 18.

Authors

Randall H Goldsmith¹, Orlando DeLeon, Thea M Wilson, Daniel Finkelstein-Shapiro, Mark A Ratner, Michael R Wasielewski

Affiliation

¹ Department of Chemistry, Argonne-Northwestern Solar Energy Research Center, and International Institute for Nanotechnology, Northwestern University, Evanston, Illinois 60208-3113, USA.

PMID: 18422290
DOI: 10.1021/jp801084v

Abstract

The temperature dependence of intramolecular charge separation in a series of donor-bridge-acceptor molecules having phenothiazine (PTZ) donors, 2,7-oligofluorene FL(n) (n = 1-4) bridges, and perylene-3,4:9,10-bis(dicarboximide) (PDI) acceptors was studied. Photoexcitation of PDI to its lowest excited singlet state results in oxidation of PTZ via the FL(n) bridge. In toluene, the temperature dependence of the charge separation rate constants for PTZ-FL(n)-PDI, (n = 1-4) is relatively weak and is successfully described by the semiclassical Marcus equation. The activation energies for charge separation suggest that bridge charge carrier injection is not the rate limiting step. The difficulty of using temperature and length dependence to differentiate hopping and superexchange is discussed, with difficulties in the latter topic explored via an extension of a kinetic model proposed by Bixon and Jortner.