Molecular Dyads of Ruthenium(II)- or Osmium(II)-Bis(terpyridine) Chromophores and Expanded Pyridinium Acceptors: Equilibration between MLCT and Charge-Separated Excited States
Molecular Dyads of Ruthenium(II)- or Osmium(II)-Bis(terpyridine) Chromophores and Expanded Pyridinium Acceptors: Equilibration between MLCT and Charge-Separated Excited States
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DOI：
10.1021/ic401639g
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发表时间：
2013-10-21
影响因子：
4.6
通讯作者：
Campagna, Sebastiano
中科院分区：
文献类型：
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作者：
Fortage, Jerome;Dupeyre, Gregory;Campagna, Sebastiano
报道了一系列四种新的分子二元体（2-5）的合成、表征、氧化还原行为和电子物理性质（室温下在流体溶液中和77 K下在刚性基质中），它们含有Ru（II）-或Os（II）-双（三联吡啶）亚基作为发色团和各种扩展的吡啶亚基作为电子受体，沿着了以前报道的二元体1的参考性质。分子二联体2-4已经被设计成具有它们的（潜在发射的）三重态金属-配体电荷转移（MLCT）和电荷分离（CS）态的能量剂量，使得这些能级之间的激发态平衡可以发生。这种情况不被极限情况1和5共享。对于二分体1，正向光诱导电子转移（时间常数，7 ps）和随后的电荷复合（时间常数，45 ps）的证据，而二分体5，光诱导电子转移是严格禁止，使MLCT衰减是唯一的主动失活过程。关于2-4，CS状态由具有几十皮秒的时间常数的MLCT状态形成。然而，对于后者的物种，这样的实验时间常数是不是由于光致电荷分离，但有关的激发态平衡时间。基于适当的热力学和动力学模型的CS状态的电荷重组的时间常数的比较分析强调，尽管他们显然附属的结构，二元体1-4不构成一个同源系列的化合物，就组分间的电子转移过程而言。
The synthesis, characterization, redox behavior, and photophysical properties (both at room temperature in fluid solution and at 77 K in rigid matrix) of a series of four new molecular dyads (2-5) containing Ru(II)- or Os(II)-bis(terpyridine) subunits as chromophores and various expanded pyridinium subunits as electron acceptors are reported, along with the reference properties of a formerly reported dyad, 1. The molecular dyads 2-4 have been designed to have their (potentially emissive) triplet metal-to-ligand charge-transfer (MLCT) and charge-separated (CS) states dose in energy, so that excited-state equilibration between these levels can take place. Such a situation is not shared by limit cases 1 and 5. For dyad 1, forward photoinduced electron transfer (time constant, 7 ps) and subsequent charge recombination (time constant, 45 ps) are evidenced, while for dyad 5, photoinduced electron transfer is thermodynamically forbidden so that MLCT decays are the only active deactivation processes. As regards 2-4, CS states are formed from MLCT states with time constants of a few dozens of picoseconds. However, for these latter species, such experimental time constants are not due to photoinduced charge separation but are related to the excited-state equilibration times. Comparative analysis of time constants for charge recombination from the CS states based on proper thermodynamic and kinetic models highlighted that, in spite of their apparently affiliated structures, dyads 1-4 do not constitute a homologous series of compounds as far as intercomponent electron transfer processes are concerned.