The library of organic photosensitizers employed in energy materials and in biomedical applications is dominated by a relatively small number of scaffolds, such as fluorescein and BODIPY, due to their well-characterized photophysics and ease of chemical functionalization. The ability to directly simulate the impact of chemical substitutions on dye photophysics in complex media would accelerate the development of high-performance organic dyes across a host of application targets. Here we present ΔDFTB, an excited-state simulation framework based on density functional tight binding (DFTB) that enables an approximate QM treatment of the environment in excited-state molecular dynamics. Benchmarks of ΔDFTB excited state geometries, vibrational frequencies, and Stokes shifts reflect a trade-off between the efficiency of the method and its accuracy for excitation energies, but excited-state properties like Stokes shifts are obtained with similar accuracy to ΔSCF-DFT at significantly reduced cost.<br/><br/>Selected applications of ΔDFTB highlight insights offered into the influence of the local electronic environment on excited-state properties of photoactive organic materials. For example, using solvatochromic shifts predicted by ΔDFTB, we can gauge the sensitivity of approximate QM/MM solvation energies to the number of QM solvent molecules. We also discuss the use of ΔDFTB for excited-state molecular dynamics sampling in the context of our efforts to elucidate a full Jablonski diagram for the sensitization of singlet oxygen by BODIPY dyes. Finally, we present a ΔDFTB-driven framework for high-throughput virtual screening which we employ in our studies of photoisomerization-based solar thermal fuels. This framework also guides our investigations of organic sensitizers for singlet fission and for quantum cutting.

Photochemistry in complex media: Insights from excited-state density-functional tight-binding

256th National Meeting (2018)

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