IDENTIFICATION OF BOTH PREEQUILIBRIUM AND DIFFUSION LIMITS FOR REACTION OF SINGLET OXYGEN, O-2(1-DELTA-G), WITH BOTH PHYSICAL AND CHEMICAL QUENCHERS - VARIABLE-TEMPERATURE, TIME-RESOLVED INFRARED LUMINESCENCE STUDIES
IDENTIFICATION OF BOTH PREEQUILIBRIUM AND DIFFUSION LIMITS FOR REACTION OF SINGLET OXYGEN, O-2(1-DELTA-G), WITH BOTH PHYSICAL AND CHEMICAL QUENCHERS - VARIABLE-TEMPERATURE, TIME-RESOLVED INFRARED LUMINESCENCE STUDIES
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DOI：
10.1021/ja00232a016
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发表时间：
1988-11-23
影响因子：
15
通讯作者：
STANDEN, MC
中科院分区：
文献类型：
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作者：
GORMAN, AA;HAMBLETT, I;STANDEN, MC
通过猝灭剂β-β使单线态氧O2（1 Δ g）失活胡萝卜素（β- C）、士的宁（S）和1，3-二苯基异苯并呋喃（DPBF）在-90%至+90 ℃的温度范围内进行了检测。C在甲苯中的时间分辨红外发光光谱。这些实验的目的是证明物理和化学猝灭剂的反应通过可逆形成的O2（1 Δ g）/猝灭剂激基复合物的中间作用进行，已经实现。涉及O2（1 Δ g）在甲苯中的扩散控制反应的活化能已经首次通过证明在低温下通过三种不同机制（电子能量转移、电荷转移诱导的系间交叉和环加成以得到内过氧化物）的淬灭表现出1.6-1.7 kcal mol-1的基本相同的Arrhenius斜率来定义。在高温下，所有三个反应都偏离扩散极限，并且在每种情况下都观察到第二线性区域。而对应于β-β的高温斜率的活化焓为C为阳性（0.4 kcal mol-1），S和DPBF明显为阴性。这些结果提供了令人信服的证据表明，在有机和生物系统中的物理和化学淬灭之间的平衡是激基复合物光物理和激基复合物光化学之间的竞争的函数。这些数据得出结论，在迄今为止没有就激活参数进行检查的淬火情况下，简单烯烃、烯醇醚、吲哚和环状二烯的那些可限制激基复合物的形成速率。用2，3-二甲基丁-2-烯（DMB）及其全氘类似物（DMB-2 H12）进行的对照实验与该结论一致。
The deactivation of singlet oxygen, O2 (1.DELTA.g), by the quenchers .beta.-carotene (.beta.-C), strychnine (S), and 1,3-diphenylisobenzofuran (DPBF) has been examined over the temperature range -90% to +90.degree. C in toluene using time-resolved infrared luminescence spectroscopy. The aim of these experiments, to demonstrate that reactions of both physical and chemical quenchers proceed via the intermediacy of a reversibly formed O2 (1.DELTA.g)/ quencher exciplex, has been achieved. The activation energy for diffusion-controlled reactions involving O2 (1.DELTA.g) in toluene has been defined for the first time by demonstrating that, at low temperature, quenchings via three different mechanisms (electronic energy transfer, charge-transfer induced intersystem crossing, and cycloaddition to give endoperoxide) exhibit essentially identical Arrhenius slopes of 1.6-1.7 kcal mol-1. At high temperature all three reactions deviate from the diffusion limit and in each case of second linear region is observed. Whereas the activation enthalpy corresponding to the high-temperature slope for .beta.-C is positive (0.4 kcal mol-1), those for S and DPBF are clearly negative. These results provide compelling evidence that the balance between physical and chemical quenching in organic and biological systems is a function of competition between exciplex photophysics and exciplex photochemistry. These data have led to the conclusion that in no cases of quenching hitherto examined in terms of activation parameters, e.g., those of simple alkenes, enol ethers, indoles, and cyclic dienes, can exciplex formation be rate-limiting. Control experiments with 2,3-dimethylbut-2-ene (DMB) and its perdeuterio analogue (DMB-2H12) are in agreement with this conclusion.