Theoretical study on photophysical properties of 3′-hydroxyechinenone and the effects of interactions with orange carotenoid protein

• Published in: Chemical physics letters Vol. 647; pp. 95 - 102
• Main Authors: Otsuka, Miho, Mori, Yukie, Takano, Keiko
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2016
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/j.cplett.2016.01.028

•Singlet excited states of a carbonyl carotenoid were studied by RASPT2 calculations.•The S1 state is 2Ag− and it gains a partial ICT character at twisted geometries.•The origin of ICT character is mixing with 1Bu+ having a large dipole moment.•Hydrogen-bonding interactions with the protein enhance the ICT character. 3′-Hydroxyechinenone (3′-hECN) is a chromophore of the orange carotenoid protein (OCP). Excitation of 3′-hECN bound to OCP to the S2(11Bu+) state yields an emission characteristic of an intramolecular charge transfer (ICT) state. The present computational results indicate that the S1 state of 3′-hECN is of the 21Ag− character and slightly gains an ICT character through the mixing with the S2(11Bu+) state when the polyene chain is twisted. Formation of hydrogen bonds with OCP enhances the 21Ag−/11Bu+ mixing and hence the ICT character in the S1 state. Such carotenoid-protein interaction may explain the observation of the ICT emission.