The Charge Transfer Phenomenon in Benzene–Pyrene–Sulfoxide/Methanol System: Role of the Intermolecular Hydrogen Bond in Excited States

Abstract

Sulfoxide is an ideal functional group containing S=O for exploring excited-state hydrogen bond dynamics. Benzene–pyrene–sulfoxide (BPS) molecule, as one of the important fluorescent chemosensors, was selected to complete the hydrogen bond dynamics of sulfoxides functional group connecting to methanol (MeOH). The ground-state and excited-state geometric structures were investigated based on density functional theory and the time-dependent density functional theory methods, respectively. The calculated absorption and emission spectra of BPS chemosensor agreed well with the experimental results, demonstrating the theory we adopted is reasonable and effective. The phenomenon of variable-length S=O and H–O bands in the first excited state (S1) as well as variable-short hydrogen bond S=O···H–O demonstrated that the intermolecular hydrogen bond were strengthened. Bathochromic shift stretching vibrational modes of both S=O and H–O regions in the S1 state manifested hydrogen bond were strengthened authentically. In addition, the frontier molecular orbitals (MOs), depicting the nature of the electronically excited states, supported that the S1 state of BPS–MeOH was a local excited state with a π–π* transition, whereas the second excited state was the charge transfer state.