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Mesoscopic structures and dynamics of merocyanine J‐aggregate studied by time‐resolved fluorescence SNOM
Author(s) -
Miura A.,
Yanagawa Y.,
Tamai N.
Publication year - 2001
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1046/j.1365-2818.2001.00879.x
Subject(s) - merocyanine , materials science , j aggregate , spin coating , fluorescence , mesoscopic physics , polymer , crystallite , composite material , analytical chemistry (journal) , optics , coating , nanotechnology , chemistry , condensed matter physics , physics , molecule , chromatography , photochromism , organic chemistry , metallurgy
Time‐resolved fluorescence SNOM is used to probe the mesoscopic structure and dynamics of long‐chain merocyanine (C 18 MC) J‐aggregates on glass plates prepared by spin coating, casting, and casting of water‐soluble polymer films. A globular structure with an average diameter of ∼ 1 µm and a height of ∼ 50 nm was attributed to the J‐aggregate of C 18 MC in the spin‐coating film. In polymer films, the bandwidth of the absorption of J‐aggregate is much narrower in polyvinyl alcohol (PVA, ∼ 20 nm) than that in polyvinyl sulphate (PVS, ∼ 60 nm). We have demonstrated that the large bandwidth of the spectrum is due to the inhomogeneous distribution of the J‐aggregate. The fluorescence image of the J‐aggregate in PVA film was rather uniform, whereas non‐uniform distribution of the fluorescence was observed in PVS film. The fluorescence of C 18 MC J‐aggregate in a small domain of PVA film was a single exponential decay with a lifetime as short as 19 ps, which was shorter than that in PVS film with a two‐exponential decay (average lifetime of ∼ 25 ps). The fluorescence lifetime of the J‐aggregate and its single exponential behaviour are considered to be indicators of the uniform distribution of the J‐aggregate. The non‐uniform distribution of the J‐aggregate in PVS film was interpreted in terms of electrostatic interaction between PVS and merocyanine.