How can Infra-Red Excitation Both Accelerate and Slow Charge Transfer in the Same Molecule?

Funding Source

National Science Foundation, Research Promotion Foundation

Grant Number

CHE-1565427,CHE-1565812, DIE-QNHSSTOXOS-0311/04


Department of Chemistry

Document Type


Publication Date



A UV-IR-Vis 3-pulse study of infra-red induced changes to electron transfer (ET) rates in a donor-bridge-acceptor species finds that charge-separation rates are slowed, while charge-recombination rates are accelerated as a result of IR excitation during the reaction. We explore the underpinning mechanisms for this behavior, studying IR-induced changes to the donor-acceptor coupling, to the validity of the Condon approximation, and to the reaction coordinate distribution. We find that the dominant IR-induced rate effects in the species studied arise from changes to the density of states in the Marcus curve crossing region. That is, IR perturbation changes the probability of accessing the activated complex for the ET reactions. IR excitation diminishes the population of the activated complex for forward (activationless) ET, thus slowing the rate. However, IR excitation increases the population of the activated complex for (highly activated) charge recombination ET, thus accelerating the charge recombination rate.


DOI: 10.1039/c8sc00092a

Funding text

The authors thank the National Science Foundation awards CHE-1565812 (DNB) and CHE-1565427 (IVR) for support of this research. The authors also thank the Cyprus Research Promotion Foundation for nancial support of the project via the research Grant “Vibrational Control of Electron Transfer DIE-QNHSSTOXOS-0311/04.” S. S. S. thanks the People Programme (Marie Curie Actions) of the European Union’s Seventh Frame-work Programme (FP7/2007–2013), under the Research Executive Agency Grant 609305. S. S. S. and D. N. B. also thank the Institute of Advanced Studies at the University of Freiburg, Germany for support.