CAS: Mechanistic Studies on How to Maximize Dipole Effects on Charge Transfer

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With support from the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Professor Valentine Vullev of the Departments of Bioengineering, Chemistry and Biochemistry at the University of California, Riverside, is developing new ways for improving the efficiency of desired charge-transferring processes while suppressing the undesired ones that lead, for example, to losses in solar-energy-conversion devices and materials. Charge transfer processes are essential, not only for sustaining life on Earth, but also for many modern technologies such as solar energy capture. Electric dipoles inherently affect charge transfer. The ubiquitous nature of dipoles, therefore, warrants deep understanding of their effects on charge transfer. Professor Vullev's group will develop optical approaches for probing and mapping the localized nanometer-scale electric fields around dipoles. Such knowledge would allow the Vullev team to quantify the dipole effects on charge transfer and to map out ways to benefit from such effects. The project lies at the interface of organic chemistry and bio-inspired molecular engineering, and is expected to provide research team member with valuable interdisciplinary training. The Vullev research group is active in outreach activities involving K-12 students, and aspires to include students from groups that have been underserved in science. This project has two objectives: (1) to develop spectroscopic approaches, using electrochromism, i.e., optical Stark effects, for probing and mapping molecular dipoles. This knowledge will allow experimental quantification of the extent to which the potentials of the electron donors and the acceptors are affected by the dipole-generated fields; (2) to study how dipole magnitude and orientation influence charge-transfer kinetics. A key pending question that this project seeks to address is the extent to which dipole effects on the rates of charge transfer change for processes with different thermodynamic driving forces, in relevance to the reorganization energy. Bio-inspired molecular electrets (systems with ordered electric dipoles) composed of different anthranilamide residues are the key structural motif for the systems designed for study in this project. In the long term, this project aims to establish important structure-function relationships for optimizing charge transfer processes of interest, allowing the molecular engineer to suppress undesired events, such as charge recombination, in the design of the system. If successful, the results this research project could impact a broad range of scientific areas, including energy conversion, bioenergetics, molecular and organic electronics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.