Indole is the aromatic side chain of tryptophan, an essential amino acid that fluoresces in the near-UV. As detailed experiments to understand the fluorescence of Trp in biochemical contexts can be difficult to perform, we are using computational quantum methods (Gaussian09 and time-dependent density functional theory) to calculate excited state properties of indole and Trp. We are testing the suitability of functionals and basis sets for calculating excitation energies, oscillator strengths, optimized geometries, and dipole moments in the well-known L<sub>a</sub> and L<sub>b</sub> excited states. The challenge is to find a method that predicts the correct ordering of these two closely spaced lowest excited states without getting “confused” during optimization, while maintaining accuracy. We further apply these methods to characterize the absorption and fluorescence spectra of indole, explore the effects of solvation on indole's fluorescence properties, and extend our work to a full tryptophan molecule.

Absorption and fluorescence of indole and tryptophan by TD-DFT

253rd National Meeting (2017)

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