Dimerization-Enhanced Excimer Probe for Wash-Free Plasma Membrane Fluorescence Imaging

Compared to monomeric counterparts, excimer probes exhibit significantly red-shifted spectra, broadened emission profiles, and enhanced Stokes shifts, exhibiting distinctive advantages in bioimaging applications. In this work, we developed an excimer-forming membrane-targeting fluorogenic probe (DIPP) through covalent conjugation between two triphenylimidazole moieties via a 1,5-bis(pyridin-1-yl)pentane linker. In various organic solvents, DIPP demonstrated exclusive excimer fluorescence, except in DMSO where monomer-excimer dual emission was observed, whereas its monomeric counterpart (MIPP) exhibits predominant monomer fluorescence, demonstrating that dimerization enhances excimer formation. Notably, DIPP displays negligible fluorescence in aqueous solution but exhibits significantly enhanced excimer emission intensity upon incorporation into SDS micelles. Leveraging the environmental sensitivity of excimer emission, DIPP was employed as a membrane-targeting fluorescent probe demonstrating multiple advantages: bright red emission (> 610 nm), a large Stokes shift (Δλ > 210 nm), low cytotoxicity, rapid cellular internalization (~ 5 min), and wash-free imaging capability.