溶剂特性对荧光材料2,5-双(6-氨基苯并恶唑-2-基)噻吩斯托克斯位移影响的密度泛函理论研究OA

In order to elucidate the solvent-dependent mechanism of the Stokes shift of the fluorescent material 2,5-bis(6-aminobenzimidazole-2-yl)thiophene(BBTA),this study employed density functional theory(DFT)and time-dependent density functional theory(TD-DFT),combined with an implicit solvent model(IEFPCM).A systematic calculation was performed on the ground-state and excited-state geometric structures,as well as the absorption and emission spectra of the BBTA molecule in the gas phase and in four distinct non-protonic solvents with varying polarities(toluene,dichloromethane,acetonitrile,and dimethyl sulfoxide).The computational re-sults demonstrate a high degree of concordance with the experimental data,exhibiting a systematic increase in the Stokes shift from 85 nm to 120 nm as the solvent polarity undergoes an increase.Mechanistic analysis indicates that the increase in Stokes shift is primarily attributed to a significant red shift in the emission spectrum,while the absorption spectrum is largely unaffected by solvent polarity.The underlying cause is attributed to the sub-stantial intramolecular charge transfer that transpires in the excited state of the BBTA molecule.This effect is fur-ther augmented during the geometric relaxation process of the excited state.It has been demonstrated that highly polar solvents exert a significant preferential stabilization effect on the more polarized excited state after relaxation through strong dipole-dipole interactions.This effect significantly reduces the energy of the system,thereby de-creasing the energy of fluorescence emission and increasing the Stokes shift.Quantitative confirmation of the pro-motion of charge separation in the relaxed excited state by polar solvents was achieved through hole-electron property analysis.This study offers significant theoretical contributions to the understanding and regulation of the photophysical properties of fluorescent materials.