RUI: Time-independent excited state methods for computational screening of photoactive materials

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Tim Kowalczyk of Western Washington University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop simulations that rapidly predict the visible-light absorption, energy conversion, and emission capabilities of organic materials. In these materials, the redirection of light energy into a flow of electrons forms the basis of emerging technologies including flexible solar cells, low-toxicity flow batteries, and noninvasive light-based therapies for the treatment of certain cancers. The research supported by this award fills a critical gap in existing methodology to enable fast computational screening of organic materials according to their photoactivity. Kowalczyk mentors a predominantly undergraduate team of student researchers in the development and application of these simulations to understand the behavior of light-absorbing materials both in isolation and in complex molecular environments. These rapid screening simulations are paired with high-accuracy modeling to uncover the details of how specialized organic dyes use the energy in light to produce the reactive oxygen species that destroy diseased tissue in photodynamic cancer therapy. Kowalczyk is linking demonstrations of simulations developed in this award to a program of undergraduate student-led energy literacy outreach in conjunction with WWU's Institute for Energy Studies.Kowalczyk and coworkers are pursuing rapid simulation strategies for photoactive materials screening through the development, benchmarking assessment, and application of time-independent excited state methods within the density-functional tight-binding (DFTB) formalism. This research seeks to transform the nascent time-independent DFTB (TI-DFTB) approach into a practical, computationally efficient strategy for photoactive materials screening as well as for multi-scale excited-state simulations in condensed phases. The TI-DFTB molecular dynamics simulations developed in this award enable efficient conformational sampling on excited-state potential energy surfaces with a self-consistent, quantum mechanical treatment of the molecular environment. Simple chemical descriptors are extracted from TI-DFTB excited-state simulations to characterize the photosensitization of singlet oxygen by a range of organic chromophores. This award supports the training and mentoring of a diverse group of undergraduate and masters-level research students at a primarily undergraduate institution.