TRIPLET AND SINGLET ENERGY-TRANSFER IN CAROTENE PORPHYRIN DYADS - ROLE OF THE LINKAGE BONDS
TRIPLET AND SINGLET ENERGY-TRANSFER IN CAROTENE PORPHYRIN DYADS - ROLE OF THE LINKAGE BONDS
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DOI：
10.1021/ja00036a002
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发表时间：
1992-05-06
影响因子：
15
通讯作者：
GOUNI, I
中科院分区：
文献类型：
--
作者：
GUST, D;MOORE, TA;GOUNI, I
制备了一系列类胡萝卜素二元体分子，其中类胡萝卜素与四芳基卟啉在内消旋芳环的邻位、间位或对位共价连接，并使用稳态和瞬态荧光发射、瞬态吸收和 H-1 NMR 方法对这些分子进行了研究。已经观察到从卟啉部分到类胡萝卜素的三重态-三重态能量转移，以及从类胡萝卜素多烯到卟啉的单重态-单重态能量转移。此外，类胡萝卜素通过增加内部转化的机制来猝灭附着的卟啉的荧光。间位异构体的所有这三个过程的速率都比相应的邻位和对位分子慢。数据分析表明，三重态-三重态能量转移是通过涉及连接键的π电子的直通键（超交换）机制介导的，而不是发色团的直接、直通空间耦合。对于导致增强内部转化的过程来说似乎也是如此。结果也与直通键机制在单线态-单线态能量转移中的作用一致。简单的休克尔分子轨道计算符合所提出的直通键合过程。
A series of carotenoporphyrin dyad molecules in which the carotenoid is covalently linked to a tetraarylporphyrin at the ortho, meta, or para position of a meso aromatic ring has been prepared, and the molecules have been studied using steady-state and transient fluorescence emission, transient absorption, and H-1 NMR methods. Triplet-triplet energy transfer from the porphyrin moiety to the carotenoid has been observed, as has singlet-singlet energy transfer from the carotenoid polyene to the porphyrin. In addition, the carotenoid quenches the fluorescence of the attached porphyrin by a mechanism which increases internal conversion. The rates of all three of these processes are slower for the meta isomer than for the corresponding ortho and para molecules. Analysis of the data suggests that the triplet-triplet energy transfer is mediated by a through-bond (superexchange) mechanism involving the pi-electrons of the linkage bonds, rather than a direct, through-space coupling of the chromophores. The same appears to be true for the process leading to enhanced internal conversion. The results are consistent with a role for the through-bond mechanism in the singlet-singlet energy transfer as well. Simple Huckel molecular orbital calculations are in accord with the proposed through-bond process.