# Excited state characterization of carbonyl containing carotenoids: a comparison between single and multireference descriptions

## TL;DR

This study compares single and multireference computational methods to characterize the excited states of six common carbonyl carotenoids, revealing the influence of the carbonyl group on their photophysical properties.

## Contribution

It provides a benchmark of DFT and multireference methods for accurately describing the excited states of carbonyl carotenoids, highlighting the effectiveness of certain functionals.

## Key findings

- The bright transition is mainly ππ* in character.
- The C=O group lowers nπ* transition energies.
- Meta-GGA functionals like M11L and MN12L perform best in benchmarking.

## Abstract

Carotenoids can play multiple roles in biological photoreceptors thanks to their rich photophysics. In the present work, we have investigated six of the most common carbonyl containing carotenoids: Echinenone, Canthaxanthin, Astaxanthin, Fucoxanthin, Capsanthin and Capsorubin. Their excitation properties are investigated by means of a hybrid density functional theory (DFT) and multireference configuration interaction (MRCI) approach to elucidate the role of the carbonyl group: the bright transition is of {\pi}{\pi}* character, as expected, but the presence of a C=O moiety reduces the energy of n{\pi}* transitions which may become closer to the {\pi}{\pi}* transition, in particular as the conjugation chain decreases. This can be related to the presence of a low-lying charge transfer state typical of short carbonyl- containing carotenoids. The DFT/MRCI results are finally used to benchmark single- reference time-dependent DFT-based methods: among the investigated functionals, the meta- GGA (and in particular M11L and MN12L) functionals show to perform the best for all six investigated systems.

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Source: https://tomesphere.com/paper/1705.01939