Abrahamsson Maria, Jäger Michael, Kumar Rohan J, Osterman Tomas, Persson Petter, Becker Hans-Christian, Johansson Olof, Hammarström Leif
Department of Photochemistry and Molecular Science, The Angström Laboratories, Uppsala University, Box 523, SE-751 20 Uppsala, Sweden.
J Am Chem Soc. 2008 Nov 19;130(46):15533-42. doi: 10.1021/ja804890k.
A series of bistridentate ruthenium(II) polypyridyl-type complexes based on the novel 2,6-di(quinolin-8-yl)pyridine (dqp) ligand have been synthesized and their photophysical properties have been studied. The complexes are amenable to substitution in the 4-position of the central pyridine with conserved quasi-C2v symmetry, which allows for extension to isomer-free, rod-like molecular arrays for vectorial control of electron and energy transfer. DFT calculations performed on the parent Ru(dqp) 2 complex (1) predicted a more octahedral structure than in the typical bistridentate complex Ru(tpy)2 (tpy is 2,2':6',2"-terpyridine) thanks to the larger ligand bite angle, which was confirmed by X-ray crystallography. A strong visible absorption band, with a maximum at 491 nm was assigned to a metal-to-ligand charge transfer (MLCT) transition, based on time-dependent DFT calculations. 1 shows room temperature emission (Phi = 0.02) from its lowest excited ((3)MLCT) state that has a very long lifetime (tau = 3 micros). The long lifetime is due to a stronger ligand field, because of the more octahedral structure, which makes the often dominant activated decay via short-lived metal-centered states insignificant also at elevated temperatures. A series of complexes based on dqp with electron donating and/or accepting substituents in the 4-position of the pyridine was prepared and the properties were compared to those of 1. An unprecedented (3)MLCT state lifetime of 5.5 micros was demonstrated for the homoleptic complex based on dqpCO2Et. The favorable photosensitizer properties of 1, such as a high extinction coefficient, high excited-state energy and long lifetime, and tunable redox potentials, are maintained upon substitution. In addition, the parent complex 1 is shown to be remarkably photostable and displays a high reactivity in light-induced electron and energy transfer reactions with typical energy and electron acceptors and donors: methylviologen, tetrathiofulvalene, and 9,10-diphenylanthracene. This new class of complexes constitutes a promising starting point for the construction of linear, rod-like molecular arrays for photosensitized reactions and applications in artificial photosynthesis and molecular electronics.
基于新型2,6 - 二（喹啉 - 8 - 基）吡啶（dqp）配体合成了一系列双齿钌（II）多吡啶型配合物，并研究了它们的光物理性质。这些配合物易于在中心吡啶的4 - 位进行取代，同时保持准C2v对称性，这使得可以扩展到无异构体的棒状分子阵列，用于电子和能量转移的矢量控制。对母体Ru(dqp)₂配合物（1）进行的密度泛函理论（DFT）计算预测，由于配体咬合角较大，其结构比典型的双齿配合物Ru(tpy)₂（tpy为2,2':6',2'' - 三联吡啶）更接近八面体结构，这一点通过X射线晶体学得到了证实。基于含时DFT计算，在491 nm处有最大吸收峰的强可见吸收带被归属于金属 - 配体电荷转移（MLCT）跃迁。1在室温下从其最低激发态（³MLCT）发射（Φ = 0.02），该激发态具有很长的寿命（τ = 3微秒）。长寿命归因于更强的配体场，这是由于更接近八面体的结构，使得通常占主导的通过短寿命金属中心态的活化衰变即使在高温下也不显著。制备了一系列基于dqp且在吡啶4 - 位带有供电子和/或吸电子取代基的配合物，并将其性质与1的性质进行了比较。基于dqpCO₂Et的均配配合物展现出前所未有的5.5微秒的³MLCT态寿命。1的良好光敏剂性质，如高消光系数、高激发态能量、长寿命以及可调的氧化还原电位，在取代后得以保持。此外，母体配合物1显示出显著的光稳定性，并且在与典型的能量和电子受体及供体：甲基紫精、四硫富瓦烯和9,10 - 二苯基蒽的光诱导电子和能量转移反应中表现出高反应活性。这类新型配合物构成了构建用于光敏反应以及人工光合作用和分子电子学应用的线性、棒状分子阵列的有前景的起点。
