ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Contributions of conformations, vibronic coupling, and hydration to photoexcitation of coumarin 334 in aqueous solution

Evgeniy S. Savenko and Victor V. Kostjukov

Physics Department, Sevastopol State University, Sevastopol, Ukraine

E-mail: viktor_kostukov@mail.ru

Received: 6 March 2022  Accepted: 24 June 2022

Abstract:

Vibronic coupling and hydrogen bonding with solvent were taken into account when analyzing the absorption of coumarin C334 in water. Both syn and anti dye conformations were considered. It turned out that the B3LYP functional in conjunction with the IEFPCM solvent description and the 6–31 +  + G(d,p) basis set provides a good prediction of the experimental spectrum. A single molecule (purely implicit solvent specification) was used as a reference for the analysis of its hydrate complexes (combined solvent specification). Upon excitation of both conformations of the dye, the rotation of the acetyl group does not occur. The conformations are separated from each other by a potential barrier with a height of about 12 kT. The addition of the second bound water molecules weakens the first H-bond. HOMOs covers water molecules bound to the nitrogen atom of the dye only. Upon excitation, the main shift of the electron density occurs from C10 to C4 neighboring atom. Thus, large-scale ICT not occur. The absolute value of the dipole moment upon excitation increases approximately 1.4…1.5 times (more for syn conformation).

Keywords: TD-DFT/DFT; Coumarin 334; Vibronic transitions; Absorption spectrum; Hydration

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-022-02357-z

Chemical Papers 76 (10) 6567–6578 (2022)