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Photophysical Behavior of Zinc(II) Tetraphenylporphyrin Covalently Incorporated in a Cholesterol‐Bearing Polymethacrylate
Author(s) -
Yusa S.,
Kamachi M.,
Morishima Y.
Publication year - 1998
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1998.tb09087.x
Subject(s) - tetraphenylporphyrin , zinc , bearing (navigation) , covalent bond , chemistry , polymer chemistry , photochemistry , porphyrin , organic chemistry , cartography , geography
Photophysical behavior of a zinc(II) tetraphenylporphyrin (ZnTPP) moiety in a copolymer of 0.1 mol % zinc(II) 5‐[4‐(6‐methacryloyloxyhexanoyloxy)phenyl]‐10,15,20‐triphenylporphynate (ZnTPP‐C 5 ‐MA) and 99.9 mol % cholesteryl 6‐methacryloyloxyhexanate (Chol‐C 5 ‐MA) was investigated in comparison with that of monomeric ZnTPP‐C 5 ‐MA. Pendant cholesterol (Chol) groups in the copolymer form stacks in n ‐hexane (a poor solvent for the copolymer), while no Chol stacks are formed in benzene (a good solvent). The absorption 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 than those in benzene. In contrast, no such solvent dependence was observed for the polymer‐bound ZnTPP moiety. Spectral profiles for the fluorescence 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 Zn‐TPP 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 compared 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 bulk solution phase.