The fate of molecular excited states: modeling donor-acceptor dyes

• Published in: Physical chemistry chemical physics : PCCP 2022-03, Vol.24 (9), p.5555-5563
• Main Authors: Giavazzi, D, Di Maiolo, F, Painelli, A
• Format: Article
• Language: English
• Subjects: Coupling (molecular); Crosstalk; Dyes; Electron states; System dynamics; Vibration
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d1cp05971h

We investigate the relaxation of a coherently excited molecule in the Redfield approximation. The molecular model, parametrized to describe donor-acceptor dyes that represent a large family of molecules of interest for several applications, accounts for two diabatic electronic states non-adiabatically coupled to a few vibrational coordinates. The proposed approach successfully describes the fast vibrational relaxation, followed by a much slower relaxation towards the ground state, a physically relevant result that is robust vs . the specific model adopted for the system-bath coupling and the specific (reasonable) choice of the bath spectral density. We demonstrate that, when dealing with more than a single vibration, it is important that each vibration is separately coupled to an independent bath so as to avoid the cross-talking of the modes through their coupling to the same bath. Provided that the overall strength of the electron-vibration coupling is maintained constant, the number of molecular vibrations introduced in the model does not affect the system dynamics, supporting the use of effective and easy models for donor-acceptor dyes accounting for a single coupled vibration. The relaxation of a coherently excited molecule with explicit vibrational modes is described in the Redfield approximation to recover the Kasha rule.