What happens right after a photoactive molecule absorbs a photon? How molecular interactions in complex condensed-phase environments influence optical and electrical responses of a molecular system? Can electronic excitations and coherence be utilized to direct energy and to control chemical reactions? We aim to develop new theoretical tools as well as molecular modeling techniques to answer these questions. Currently, there are four major themes in our study.
Dynamics of light harvesting
Photosynthetic organisms utilize sophisticatedly constructed pigment-protein complexes to absorb sun light and conduct energy to the reaction center in near unity quantum efficiency. We aim to understanding the molecular mechanisms that enable this extremely efficient process and to gain new insights that can improve artificial light-harvesting devices. Here, we need to develop theories for excitation energy transfer that cover a broad parameter range and to use molecular modeling to elucidate how the protein environment influence electronic excitations.
Photon-induced chemical dynamics
Photon-induced chemical dynamics are usually ultrafast, highly non-equilibrium, and nonadiabatic. This situation is far from the applicability of conventional Arrhenius dynamics and it opens up tremendous opportunities for coherent control and novel chemical transformation. We use mixed quantum-classical methods to study nonadiabatic chemical dynamics of molecular systems in highly constrained condensed-phase environments, such as in proteins and nanoreactors. The aim is to elucidate fundamental principles of chemical control of excited-state dynamics for new types of photochemistry.
Theory for ultrafast nonlinear spectroscopy
Time-resolved ultrafast spectroscopies are main techniques for experimental investigations of molecular interactions and dynamics in the condensed phase. For example, recent optical nonlinear experiments have provided critical information on light-harvesting in photosynthesis and ultrafast photo-chemistry in vision. Because of the complexity of these experiments, theoretical modeling and computer simulations are required to develop molecular-level descriptions of the underlying processes. We aim to develop new theoretical methods that enable the calculation of nonlinear spectra of molecular systems directly based on light-driven dynamics described by a quantum master equation formalism. Multidimensional electronic spectra for non-adiabatic systems evaluated in this way will be valuable for guiding and interpreting future experiments.
Multi-scale modeling of optoelectronic nano-materials
Photoactive molecular architectures have recently attracted intensive research interests in Chemistry and Nanoscience because of their potential to achieve extraordinary optoelectronic properties. Despite intensive research, the rational design of photoactive molecular materials is still very much under development. The main roadblock here is the lack of a fundamental understanding of the excitation energy transfer and charge transfer dynamics in these complex molecular systems. A robust theoretical approach that can predict bulk optical and electronic properties of molecular materials, e.g., absorption spectrum and charge-carrier mobilities, from chemical structure of their molecular subunits entails multiple major challenges in theoretical chemistry, and we aim to develop multi-scale methodologies that will enable us to simulate electronic dynamics in complex condensed-phase molecular systems with molecular detail. We will apply these theoretical tools to investigate fundamental questions regarding how the molecular architectures and fluctuations affect electronic quantum dynamics in the condensed phase, and eventually to formulate new physical insights that can be translated into more fundamental and transferable knowledge.