Controlling Electron Transfer Direction Using Light

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

DESCRIPTION (provided by applicant): The proposed research combines state of the art physical methods with rational synthetic design principles in order to demonstrate active control over rates and spatial direction of photo-induced electron transfer in complex model and biological systems. The methodology is rooted in the idea that coherent light fields can be used to guide molecular systems to arbitrary target products desired by the experimenter. Because these fields are difficult to predict, a self-learning procedure is implemented which combines 1) many-parameter control over laser field shapes using femtosecond pulse shaping technology, 2) measurement of the experimental response to be used as a feedback signal sensitive to the success of the pulse shapes, and 3) a general search algorithm to evaluate pulse shapes in the vast search space. In the iteration of these steps, the molecules guide the search for an optimal field within the constraints of the Hamiltonian and the experimental conditions. For the purposes of controlling the spatial direction of photo-induced electron transfer, it is necessary to design and synthesize chromophores exhibiting structural and electronic asymmetry while introducing spectroscopic signals sensitive to charge localization in distinct regions of the molecule. The initial research will use model Donor-Acceptor systems to address whether photo-induced electron transfer rates can be altered/controlled in the first place. This will be followed by attempts to control the direction electron transfer within Acceptor-Donor-Acceptor' systems exhibiting multiple pathways for movement of charge. The knowledge gained in these studies will then be used to implement arbitrary control over the direction of electron transfer in the reaction center of photosynthetic purple bacteria. Such control will allow for the production of metastable intermediates not observed in native proteins and may offer new directions for energy conversion.