Identification of H-aggregate in a monolayer amphiphilic porphyrin-TiO2 nanoparticle heterostructure assembly and its influence on the photoinduced charge transfer

The spectral properties of the monolayer 5,10,15-tri(4-hydroxyphenyl)-20-(4 -hexadecyloxyphenyl) porphyrin molecule (TriHHP)-TiO2 nanoparticle heterost ructure assembly were investigated with absorption, fluorescence emission a nd excitation spectra, in comparison with those of CHCl3 solution and monol ayer films deposited from pH 3 and pH 10 water subphases. A new fluorescenc e emission band, arising from a blue-shifted Q-absorption band, was observe d in the assembly or the monolayer film deposited from pH 3 water subphase. An H-aggregate type species from the protonated TriHHP molecules was assig ned to cause this new emission band. According to the Frontier orbital theo ry, this H-aggregate is suggested in the configuration of face-to-face pi-p i stacking interaction among the protonated TriHHP molecules. In the hetero structure assembly, the efficient fluorescence emission quenching of TriHHP by the photoinduced charge transfer occurs under excitation in Soret band region of the unprotonated TriHHP molecules. No contribution to the photoin duced charge transfer. (C) 2000 Elsevier Science S.A. All rights reserved.