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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Formation of O_2(~1Σ_g~+), O_2(~1Δ_g), and O_2(~3Σ_g~-) during Oxygen Quenching of nπ~* Triplet Phenyl Ketones: The Role of Charge Transfer and Sensitizer-Oxygen Complex Structure
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Formation of O_2(~1Σ_g~+), O_2(~1Δ_g), and O_2(~3Σ_g~-) during Oxygen Quenching of nπ~* Triplet Phenyl Ketones: The Role of Charge Transfer and Sensitizer-Oxygen Complex Structure

机译：在nπ〜*三重态苯基酮的氧猝灭过程中O_2（〜1Σ_g〜+），O_2（〜1Δ_g）和O_2（〜3Σ_g〜-）的形成：电荷转移和敏化剂-氧复合物的作用

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摘要

Rate constants of formation of O_2(~1Σ_g~+), O_2(~1Δ_g), and O_2(~3Σ_g~-) in the quenching of triplet states T_1 by O_2 have been determined for a series of nine benzophenones (BPs) of strongly varying oxidation potential, E_(ox), but almost constant triplet-state energy E_T. These data are analyzed considering data determined previously for T_1(ππ~*) sensitizers of very different E_T and E_(ox). Much weaker charge transfer (CT) effects are observed for the T_1(nπ~*) BPs compared with those obtained with a series of structurally related T_1(ππ~*) biphenyls. The quenching proceeds for T_1(nπ~*) and T_1(ππ~*) sensitizers via two different channels, each capable of producing O_2(~1Σ_g~+), O_2(~1Δ_g), and O_2(~3Σ_g~-). One channel originates from excited ~(3,3)(T_1·~3Σ) complexes with no CT character and the other from ~(3,3)(T_1·~3Σ) exciplexes with partial CT character. Different energy gap relations determine the formation of O_2(~1Σ_g~+), O_2(~1Δ_g), and O_2(~3Σ_g~-) of T_1(ππ~*) and T_1(nπ~*) sensitizers in the nCT channel, whereby the excess energy (ΔE) dependence of the corresponding rate constants is much weaker for the T_1(nπ~*) ketones. In the pCT channel, the respective rate constants vary on a logarithmic scale linearly with the free energy change for complete electron transfer for both T_1(ππ~*) and T_1(nπ~*) sensitizers. This dependence too is much weaker for T_1(nπ~*) than for T_1(ππ~*) sensitizers. The comparison with CT induced quenching of O_2(~1Δ_g) by ground-state sensitizers reveals that the different electronic configurations leads to different sterical structures of ~(1,3)(T_1(nπ~*)·~3Σ) and ~(1,3)(T_1(ππ~*)·~3Σ) complexes. These differences strongly influence the complex deactivation and explain both the weaker ΔE dependence and the weaker CT effects in the quenching of T_1(nπ~*) by O_2.
机译：对于一系列九个强力的二苯甲酮（BPs），已经确定了O_2在三重态T_1被O_2猝灭中形成O_2（〜1Σ_g〜+），O_2（〜1Δ_g）和O_2（〜3Σ_g〜-）的速率常数。氧化电位E_（ox）变化，但三重态能量E_T几乎恒定。考虑到先前为非常不同的E_T和E_（ox）的T_1（ππ〜*）敏化剂确定的数据，对这些数据进行了分析。与使用一系列与结构相关的T_1（ππ〜*）联苯获得的BP相比，T_1（nπ〜*）BP的电荷转移（CT）效应要弱得多。通过两个不同的通道对T_1（nπ〜*）和T_1（ππ〜*）敏化剂进行淬灭，每个通道都能产生O_2（〜1Σ_g〜+），O_2（〜1Δ_g）和O_2（〜3Σ_g〜-）。一个通道来自无CT特性的〜（3,3）（T_1·〜3Σ）激发复合物，另一通道来自具有CT部分特性的〜（3,3）（T_1·〜3Σ）激基复合物。不同的能隙关系决定了nCT通道中T_1（ππ〜*）和T_1（nπ〜*）敏化剂的O_2（〜1Σ_g〜+），O_2（〜1Δ_g）和O_2（〜3Σ_g〜-）的形成，因此，对于T_1（nπ〜*）酮，相应速率常数的过量能量（ΔE）依赖性要弱得多。在pCT通道中，对于T_1（ππ〜*）和T_1（nπ〜*）增感剂，相应的速率常数随自由能的变化呈对数线性变化，以实现完全的电子转移。对于T_1（nπ〜*）来说，这种依赖性也比对T_1（ππ〜*）敏化剂的依赖性弱得多。与基态敏化剂与CT诱导的O_2（〜1Δ_g）猝灭的比较表明，不同的电子构型导致〜（1,3）（T_1（nπ〜*）·〜3Σ）和〜（1 ，3）（T_1（ππ〜*）·〜3Σ）复合。这些差异极大地影响了复杂的失活，并解释了O_2淬灭T_1（nπ〜*）时，ΔE依赖性较弱，CT效应较弱。

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