Troy Van Voorhis of the Massachusetts Institute of Technology is supported by an award from the Theory, Models and Computational Methods Program to develop, implement and apply transformative tools for modeling photochemical processes in complex environments. In particular, Van Voorhis and his research group focus on extending the techniques of ground state electronic structure theory to the accurate treatment of electronic excited states. They employ these new methods to understand three key photochemical processes: excited state intramolecular electron transfer (ET), ultrafast fluorescence spectroscopy and nonradiative quenching of dyes. They use constrained density functional theory (DFT) as a framework for simulating electron transfer. To describe fluorescence spectra and the dynamic Stokes shift they are developing a hybrid of novel DFT and wave function techniques. The simulations are among the most ambitious studies of condensed phase photochemical dynamics attempted to date.

This research is developing a palette of general, widely applicable techniques for the accurate description of photochemistry in solution. The techniques developed in the course of this research are applicable to molecules that play key functional roles in photosynthesis, organic light-emitting diodes (LEDs) and chemical sensing. Researchers around the world will have access to these methods through the Q-Chem package of programs, making the potential impact essentially limitless. Graduate students and postdoctoral associates are being trained in this project. The PI and his group also produce, for a general audience, web-based short films based on their research projects.

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Project Report

One of the most powerful principles of modern chemistry is that complex macroscopic transformations can always be broken down into individual microscopic steps that determine the overall efficiency of the process. Thus, for example, the intricate dynamics of photosynthetic light harvesting complexes, light emitting diodes (LEDs) and molecular electrical conductors are commonly composed of only a few fundamental steps: charge separation/recombination, energy transfer and excited state bond-making. In order to obtain vital insight into these photochemical processes, one must extend the powerful techniques of ground state electronic structure theory into the relatively uncharted waters of excited state molecular dynamics. The task is complicated by the fact that a successful picture of these complex condensed phase reactions requires input from all areas of theoretical chemistry – electronic structure, quantum dynamics and statistical mechanics alike. The work in this project answered this challenge by developing new first principles methods that will provide an accurate description of electronic excited state motion in complex condensed phase environments. These tools make it possible to describe many photochemical processes: intramolecular electron transfer (ET) reactions, ultrafast fluorescence relaxation and nonradiative quenching via charge transfer. Each of these microscopic processes is of profound technological relevance: ET plays a central role in photovoltaic and photosynthetic architectures; ultrafast relaxation protects molecules from radiation damage and accounts for the color purity of organic LEDs; and fluorescence quenching is the basis of many novel chemical sensors. The theoretical investigations presentd here provide key insights into the atomistic mechanisms that control these applications, paving the way for advances in solar energy conversion, organic light emission and chemical sensing. In particular, the work here accomplished four methodological advances: 1) The project enhanced our infrastructure for doing constrained DFT simulations by implementing analytic forces that facilitate molecular dynamics 2) The work validated nonlocal density functionals for intermolecular interactions 3) The investigators implements projected and self-consistent mean field methods that treat static and dynamic correlation on an equal footing for both ground and excited states 4) The project extended the use of high order master equations for condensed phase quantum dynamics. Beyond these case studies, the project introduced new educational advances through the introduction of blended learning elements in the physical chemistry curriculum and through outreach to at-risk high school students through the REACH program.

Agency
National Science Foundation (NSF)
Institute
Division of Chemistry (CHE)
Application #
1058219
Program Officer
Evelyn Goldfield
Project Start
Project End
Budget Start
2011-02-01
Budget End
2015-01-31
Support Year
Fiscal Year
2010
Total Cost
$455,000
Indirect Cost
Name
Massachusetts Institute of Technology
Department
Type
DUNS #
City
Cambridge
State
MA
Country
United States
Zip Code
02139