A fundamental understanding of charge separation is necessary for the rational design of organic optoelectronic devices. Computational approaches provide fundamental insights into these processes, which in turn guide the synthesis of novel optoelectronic materials. Conventional density functional theory (DFT) methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems.  In order to address these failures, we implement the BNL (Baer-Neuhauser-Livshits) range-separated hybrid (RSH) functional approach within DFT and time-dependent DFT.The RSH approach was benchmarked using a model ethene dimer and silsesquioxane molecules currently investigated as candidates for building blocks in photovoltaic applications. The RSH approach successfully reproduced empirical energies and trends, where the conventional functionals had been shown to fail.To account for complex environmental effects on charge transfer energies in silsesquioxane molecules, a protocol was developed that combines charge-constrained DFT, a polarizable continuum solvent model, and RSH DFT. The protocol was tested and validated by comparing the calculated charge transfer state energies to experimental measurements on silsesquioxane molecules. This method provides a way to understand charge transfer within complex environments for molecules used in photovoltaic applications, and is currently being extended to other silsesquioxane systems.The RSH approach was also applied to newly proposed phosphorescent organic light emitting diode systems, including dibenzophoshole chalcogenide and bromobenzaldehyde derivatives, in order to provide insight into transport properties of these materials. Triplet energies calculated using RSH DFT offer improved agreement with experimental values compared to conventional DFT functionals. Current work is focused on determining the mechanism underlying the directed-heavy atom effect in bromobenzaldehyde materials.

Predictive computational methods for charge transfer in organic optoelectronic materials

246th National Meeting (2013)

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