Centre for Advanced Electron Spin Resonance (CAESR), University of Oxford , South Parks Road, Oxford OX1 3QR, United Kingdom.
Chemistry Research Laboratory, Department of Chemistry, University of Oxford , 12 Mansfield Road, Oxford OX1 3TA, United Kingdom.
J Am Chem Soc. 2017 Aug 30;139(34):12003-12008. doi: 10.1021/jacs.7b06518. Epub 2017 Aug 15.
The extent of triplet state delocalization is investigated in rigid linear zinc porphyrin oligomers as a function of interporphyrin bonding characteristics, specifically in meso-meso singly linked and β,meso,β fused structures, using electron paramagnetic resonance techniques. The results are compared with those of earlier measurements on porphyrin oligomers with alkyne linkers exhibiting different preferred conformations. It is shown that dihedral angles near 90° between the porphyrin planes in directly meso-to-meso linked porphyrin oligomers lead to localization of the photoexcited triplet state on a single porphyrin unit, whereas previous work demonstrated even delocalization over two units in meso-to-meso ethyne or butadiyne-bridged oligomers, where the preferred dihedral angles amount to roughly 30° and 0°, respectively. The triplet states of fused porphyrin oligomers (i.e., porphyrin tapes) exhibit extended conjugation and even delocalization over more than two porphyrin macrocycles, in contrast to meso-to-meso ethyne or butadiyne-bridged oligomers, where the spin density distribution in molecules composed of more than two porphyrin units is not evenly spread across the oligomer chain.
作为研究卟啉分子间键合特性的一部分，我们采用电子顺磁共振技术，研究了刚性线性锌卟啉低聚物中三重态离域的程度。我们比较了具有不同优势构象的炔键连接的卟啉低聚物的早期测量结果。结果表明，在直接通过间位连接的卟啉低聚物中，卟啉平面之间的二面角接近 90°，导致光激发三重态局域在单个卟啉单元上，而之前的工作表明，在间位乙炔或丁二炔桥联的低聚物中，即使在两个单元上也能离域，其中优选的二面角分别约为 30°和 0°。与间位乙炔或丁二炔桥联的低聚物相比，稠合卟啉低聚物（即卟啉带）的三重态表现出扩展的共轭作用，甚至在两个以上卟啉大环上离域，在这些低聚物中，由两个以上卟啉单元组成的分子中自旋密度分布不会均匀地分布在低聚物链上。
