Toward a Realistic Modeling of the Photophysics of Molecular Building Blocks for Energy Harvesting: The Charge-Transfer State in 4,7-Dithien-2-yl-2,1,3-benzothiadiazole As a Case Study

Theoretical modeling of the photophysical properties of materials (both low-weighted and polymeric) for energy harvesting represents an attractive area of fundamental and applied research. In this area meaningful results can be obtained only in the presence of realistic models keeping intact the atomistic complexity which, in this system, is usually very high. Herein we propose a model study, carried out on a typical building block for energy harvesting materials, 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTB), with the precise aim to theoretically reproduce the charge-transfer S0–S1 UV–vis signal in different solvents and also to provide some hints for interpreting the large Stokes-shift observed in its fluorescence spectra. Results show that the DTB spectral (absorption) features are the result of an intimate interplay between chromophore thermal fluctuations and environmental dynamical (electrostatic) perturbation. Deep inspection of the results also confirms the possibility of modulating the chromophore low-energy photophysics acting on the thermal, electrical, and chemical properties of the molecular surrounding environment.