PHOTOPHYSICAL BEHAVIOR OF ZINC(II) TETRAPHENYLPORPHYRIN COVALENTLY INCORPORATED IN A CHOLESTEROL-BEARING POLYMETHACRYLATE

Photophysical behavior of a zinc(II) tetraphenylporphyrin (ZnTPP) moie ty in a copolymer of 0.1 mol % zinc(II) xyhexanoyloxy)phenyl]-10,15,20 -triphenylporphynate (ZnTPP-C-5-MA) and 99.9 mol % cholesteryl 6-metha cryloyloxyhexanate (Chol-C-5-MA) was investigated in comparison with t hat of monomeric ZnTPP-C-5-MA. Pendant cholesterol (Chol) groups in th e copolymer form stacks in n-hexane (a poor solvent for the copolymer) , while no Chol stacks are formed in benzene (a good solvent). The abs orption maxima of the Soret and Q bands of monomeric ZnTPP-C-5-MA were solvent dependent, i.e. the maxima in n-hexane were 7.6 nm shorter th an those in benzene. In contrast, no such solvent dependence was obser ved for the polymer-bound ZnTPP moiety, Spectral profiles for the fluo rescence bands for the polymer-bound ZnTPP moiety and monomeric ZnTPP- C-5-MA were very different in n-hexane, i.e. the relative intensity of the 0-0 to 0-1 fluorescence bands for the former was 0.52 while that for the latter was 1.10, The triplet excited lifetime for the polymer- bound ZnTPP moiety at room temperature was much longer in n-hexane (22 ms) than in benzene (3.7 ms), while the fluorescence lifetime at room temperature was slightly longer in n-hexane (2.52 ns) than in benzene (2.09 ns), The polymer-bound ZnTPP moiety emitted phosphorescence and E-type delayed fluorescence in n-hexane at room temperature, arising from the long triplet lifetime. Fluorescence quenching for the polymer -bound ZnTPP moiety by vitamin-K-3 was suppressed in n-hexane, as comp ared to the quenching of the monomer. All these observations indicate that the ZnTPP chromophores in the copolymer are ''protected'' in the Chol stacks in n-hexane, leading to an isolation of ZnTPP from the bul k solution phase.