Impacts of Environmental Rigidity on Photophysical Characteristics and Behaviors of a Quadrupolar Chromophore Revealed by Single-Molecule Fluorescence Spectroscopic Study

Abstract

Multipolar chromophores (e.g., quadrupolar and octupolar molecules) have excellent two-photon absorption properties and exhibit characteristic excited-state relaxation behaviors that involve structural symmetry breaking. Environmental rigidity could provide an appreciable impact on such conformational rearrangement in the excited state; however, details of its effect remain unclear. Herein, we undertake an ensemble and single-molecule spectroscopic investigation into the effects of environmental rigidity on the photophysical characteristics and behaviors of a newly synthesized D−π–A−π–D (donor−π–acceptor−π–donor) quadrupolar chromophore, QC, and its π–A−π analogue, AC, in various solutions and polymers. The fluorescence emission of QC in nonpolar solvents takes place in the symmetric quadrupolar state [Dδ+–π–Aδ−–π–Dδ+]*, whereas the significant fluorescence quenching is observed with increasing solvent polarity, suggesting the gradual stabilization of the nonemissive symmetry-broken dipolar state [Dδ+–π–A...