Single-molecule fluorescence dynamics of a butadiyne-linked porphyrin dimer: The effect of conformational flexibility in host polymers

We have investigated the single-molecule fluorescence dynamics of a butadiyne-linked porphyrin dimer (Z2B) depending on the density of the poly(methyl methacrylate) (PMMA) matrix (5, 10, 25, and 50 mg ml ^-1). By recording single-molecule fluorescence intensity trajectories and fluorescence lifetimes, we observed more frequent one-step photobleaching behavior, less frequent on-off behavior, and narrower fluorescence lifetime distributions in lower densities of PMMA polymer. In contrast, more enhanced photostability was observed in higher densities of PMMA polymer. These results are explained by a difference in the molecular surroundings depending on the change in PMMA polymer density, suggesting that the individual photophysical properties of Z2B are strongly associated with their conformations and molecular surroundings in the solid state. Our studies will provide further information on the structure/surroundings relationship of single molecules in the solid state.