Mesoscopic structures and dynamics of merocyanine J-aggregate studied by time-resolved fluorescence SNOM

Time-reserved fluorescence SNOM is used to probe the mesoscopic structure a nd dynamics of long-chain merocyanine (C18MC) J-aggregates on glass plates prepared by spin coating, casting, and casting of water-soluble polymer fil ms. A globular structure with an average diameter of similar to1 mum and a height of similar to 50 nm was attributed to the J-aggregate of C18MC in th e spin-coating film. in polymer films, the bandwidth of the absorption of J -aggregate is much narrower in polyvinyl alcohol (PVA, similar to 20 nm) th an that in polyvinyl sulphate (PVS, similar to 60 nm). We have demonstrated that the large bandwidth of the spectrum is due to the inhomogeneous distr ibution of the T-aggregate. The fluorescence image of the T-aggregate in PV A film was rather uniform, whereas non-uniform distribution of the fluoresc ence was observed in PVS film. The fluorescence of C18MC J-aggregate in a s mall domain of PVA film was a single exponential decay with a lifetime as s hort as 19 ps, which was shorter than that in PVS film with a two-exponenti al decay (average lifetime of similar to 25ps). The fluorescence lifetime o f the J-aggregate and its single exponential behaviour are considered to be indicators of the uniform distribution of the J-aggregate. The nonuniform distribution of the J-aggregate in PVS film was interpreted in terms of ele ctrostatic interaction between PVS and merocyanine.