Intramolecular energy transfer in molecular dyads comprising free-base porphyrin and ruthenium(II) bis(2,2′:6′,2"-terpyridine) termini
Intramolecular energy transfer in molecular dyads comprising free-base porphyrin and ruthenium(II) bis(2,2′:6′,2"-terpyridine) termini
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DOI：
10.1021/jp047400j
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发表时间：
2004-10-21
影响因子：
2.9
通讯作者：
Mehrabi, M
中科院分区：
文献类型：
--
作者：
Benniston, AC;Chapman, GM;Mehrabi, M
本文合成了一种由卟啉和钌（Ⅱ）双（2，2 '：6'，2”-三联吡啶）亚基通过meso-亚苯基连接而成的分子二元体。末端三联吡啶配体具有单个苯基亚乙炔基。选择性照射到金属络合物中之后是从金属-配体电荷转移（MLCT）三重态到最低能量pi、pi* 三重态局部化的卟啉的快速分子内三重态-三重态能量转移。该过程的特征在于重组能为0.14 eV，电子耦合矩阵元为76 cm（-1）。由于亚炔基取代基，最初产生的MLCT状态集中在远端三联吡啶上。因此，三重态能量转移必须穿过近端三联吡啶配体。在低温下，核隧穿使得三重态能量转移的速率不活化。在选择性照射到位于卟啉上的最低能量单线态（S-1）时，发生快速单线态-三线态能量转移，以高效率填充MLCT三线态。该过程在室温下通过德克斯特型电子交换发生，并且MLCT三重态可以在低温下被鉴定为反应中间体。由于能隙较小，单重态-三重态能量转移的活化能仅为0.05eV，电子耦合矩阵元减小到11 cm（-1），因为能量转移是自旋禁戒的。在低温下，偶极-偶极能量转移成为卟啉S-1态衰变的主要机制。激发进入卟啉的Soret带后快速内转换为S-1，而没有能量或电子转移到附加的金属络合物。
A molecular dyad has been synthesized in which free-base porphyrin and ruthenium(II) bis(2,2':6',2"-terpyridine) subunits are linked via a meso-phenylene group. The distal terpyridine ligand bears a single phenylethynylene group. Selective illumination into the metal complex is followed by rapid intramolecular triplet-triplet energy transfer from the metal-to-ligand charge-transfer (MLCT) triplet to the lowest-energy pi,pi* triplet state localized oil the porphyrin. This process is characterized by a reorganization energy of 0.14 eV and an electronic coupling matrix element of 76 cm(-1). Because of the alkynylene substituent, the initially produced MLCT state is centered on the distal terpyridine. Therefore, triplet energy transfer must cross the proximal terpyridine ligand. At low temperature, nuclear tunneling renders the rate of triplet energy transfer activationless. Upon selective illumination into the lowest-energy singlet (S-1) state localized on the porphyrin, fast singlet-triplet energy transfer occurs, to populate the MLCT triplet with high efficiency. This process happens by way of Dexter-type electron exchange at room temperature, and the MLCT triplet can be identified as a reaction intermediate at low temperature. The activation energy for singlet-triplet energy transfer is only 0.05 eV, because of the smaller energy gap, and the electronic coupling matrix element is decreased to 11 cm(-1), because energy transfer is spin-forbidden. At low temperature, dipole-dipole energy transfer becomes the main mechanism for decay of the porphyrin S-1 state. Excitation into the Soret band of the porphyrin is followed by rapid internal conversion to S-1 without energy or electron transfer to the appended metal complex.