The electronic structure and photophysical properties of a series of N-Methyl and N-Acetyl substituted alloxazine (AZs) were investigated with extensive density functional theory (DFT) and time-dependent density functional theory (TD-DFT) based calculations. We showed that non-radiative decay from singlet and triplet excited states of these AZs are dominant over their radiative counterparts. The fast non-radiative decay of excited AZs can be attributed to the energy consumption (Ereorg) through structural reorganization facilitated by intrinsic normal modes of alloxazine framework, as well as their coupling with those of the functional groups. Substitution with functional groups of large spin-orbital coupling constants, such as acetyl, may effectively enhance intersystem crossing properties of AZs. Due to different bonding of N1 and N3 within the alloxazine framework, substitution may result in AZs of different photophysical properties. Specifically, functionalization at N1 may help to maintain or even reduce Ereorg and would promote the absorption and radiative decay from excited AZs. However, the strong coupling of vibrational modes of acetyl at N3 with the intrinsic normal modes of alloxazine framework would contribute significantly to Ereorg, and benefit the non-radiative decay of excited AZs. We expect the findings would pave the way for rational design of novel AZs with extraordinary photophysical properties.

Photophysical properties of N-methyl and N-acetyl substituted alloxazine: A theoretical investigation

ACS Fall 2021

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