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Excitation energy transfer of porphyrin in polymer thin films by time‐resolved scanning near‐field optical microspectroscopy
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.1365-2818.2001.00870.x
Subject(s) - excitation , polymer , spin coating , thin film , porphyrin , chromophore , fluorene , perylene , optical microscope , materials science , chemistry , molecular physics , analytical chemistry (journal) , fluorescence , chemical physics , optics , scanning electron microscope , nanotechnology , photochemistry , physics , chromatography , electrical engineering , composite material , engineering
Thin films of water‐soluble free‐base porphyrin, 5,10,15,20‐tetraphenyl‐21H, 23H‐porphinetetrasulphonic acid (TPPS) mixed with poly(diallyldimethyl ammonium chloride) (PDDA) have been prepared by a spin‐coating method, in which the monomeric species were observed in the spin‐coat film, whereas dimer was formed in the cast film prepared from TPPS/PDDA solution. Mesoscopic structures and dynamics of excitation energy migration and trapping of TPPS/PDDA spin‐coat film have been analysed by time‐resolved scanning near‐field optical microspectroscopy (SNOM) and atomic force microscope. The observed film structure can be classified roughly into two parts: one is a large, flocculated polymer part, and the other is a smooth part widely spread around the flocculated polymers. In the smooth part, the observed spindle‐like structure and circular hills and dips are essentially due to PDDA. The ellipsoidal small structures with ∼2µm length and <1 µm width in the flocculated polymer part show non‐exponential fluorescence decays. The non‐exponential dynamics originates from the excitation energy migration among TPPS monomers and energy trapping to dimers. From the analysis of fluorescence decay curves based on the equation developed by Klafter and Blumen, the spectral dimension has been estimated to be ∼1.46 for ellipsoidal structures. These results indicate that the distribution of the chromophore is inhomogeneous and a fractal‐like structure exists even in the small domains determined by the resolution of the SNOM tip.