Scaling Relations Related to the Kinetics of Excimer Formation between Pyrene Groups Attached onto Poly(N,N-dimethylacrylamide)s

The fluorescence decays of the pyrene monomer of a series of pyrene-labeled poly(N,N-dimethylacrylamide)s (PyPDMAAm) were acquired in N,N-dimethylformamide (DMF) and acetone with different concentrations of nitromethane and at very low polymer concentration. DMF and acetone are good and mediocre solvents for PyPDMAAm, respectively. Nitromethane is a potent quencher of pyrene. Nitromethane addition to the polymer solution shortens the pyrene lifetime. The fluorescence decays of the quenched and unquenched pyrene-labeled polymers were analyzed with a blob model. Shortening the lifetime of pyrene reduces the volume probed by the dye while it remains excited. For each quencher concentration, the blob volume and size were determined, and scaling laws were shown to hold. The exponents retrieved from the scaling relationships agreed with those reported in polymer science textbooks.