Fluorescence Lifetime-Based Characterization for Supramolecular Polymer Molecular Weight

The determination of molecular weight is crucial for understanding the properties of supramolecular polymers, but it poses challenges due to their concentration-dependent dynamic behavior. In this study, a specific viscosity-fluorescence lifetime technique was employed using 4,4'-difluoro-4-bora-3a,4adiaza-s-indacene (BODIPY-C12a) as a molecular weight probe. At lower concentrations, supramolecular polymers existed as short chains, gradually elongating with increasing monomer concentration, indicating higher molecular weights. The viscosity of the system correlated with the molecular weight. Incorporating BODIPY-C12a, which is sensitive to viscosity, exhibited distinct changes in fluorescence lifetime due to the restriction of phenyl ring rotation at higher concentrations. By analyzing fluorescence lifetime, molecular weight could be determined. Furthermore, trifluoroacetic acid disrupted quadruple hydrogen bonding, leading to supramolecular polymer disassembly and a decrease in fluorescence lifetime.