ANOMALOUSLY BLUE-SHIFTED FLUORESCENCE AND PHOSPHORESCENCE OF ZINC(II) TETRAPHENYLPORPHYRIN IN HIGHLY CONSTRAINING MICROENVIRONMENTS IN HYDROPHOBICALLY-MODIFIED POLYSULFONATES

Zinc(II) tetraphenylporphyrin (ZnTPP) moieties, covalently attached to amphiphilic sodium polysulfonates carrying cyclododecyl (Cd; 60 mol %) or lauryl (La; 61 mol %) groups, are compartmentalized within the clusters of the hydrophobic groups in aqueous solution. Such compartmentalized ZnTPP chromophores exhibit delayed fluorescence and phosphorescence at ordinary temperatures. The spectral patterns of the fluorescence and phosphorescence of the ZnTPP moieties in the Cd cluster strongly depended on the excitation wavelength; anomalously blue-shifted fluorescence (both prompt and delayed) and phosphorescence spectra were observed when excited at wavelengths on the shorter wavelength side of the Soret band maximum, while these emissions showed normal spectra when excited at wavelengths on the red side of the Soret band maximum. No such dependencies of the emission spectra on the excitation wavelength were recognized for the ZnTPP moieties compartmentalized in the La cluster. The spectral data indicate that the microenvironment about the ZnTPP chromophores in the Cd cluster is markedly different from that in the La cluster and that there are ZnTPP species whose electronic energy levels are considerably perturbed in the Cd cluster. These species are ascribed to conformationally distorted ZnTPP species owing to the highly constraining microenvironments in the Cd cluster.