Comparative study of the photophysical properties of nonplanar tetraphenylporphyrin and octaethylporphyrin diacids
Comparative study of the photophysical properties of nonplanar tetraphenylporphyrin and octaethylporphyrin diacids
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DOI：
10.1021/jp001631i
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发表时间：
2000-10-26
影响因子：
3.3
通讯作者：
Holten, D
中科院分区：
文献类型：
--
作者：
Chirvony, VS;van Hoek, A;Holten, D
研究了两种卟啉二酸的最低激发单重态S-1（pi，pi*）的电子物理性质。二酸是H4 TPP 2+和H4 OEP 2+，分别是游离碱四苯基卟啉（H2 TPP）和八乙基卟啉（H2OEP）的双质子化形式。这两种二元酸表现出扰动的静态和动态特性相对于在室温下的溶液中的母中性配合物。这些性质包括提高的S-1 - S-0无辐射失活（内转化）产率，其从H2 TPP和H2OEP的近似0.1增加到H4 OEP 2+的0.4和H4 TPP 2+的0.6。这两种二元酸的荧光寿命都强烈地依赖于温度，S-1态失活的活化焓接近1400 cm（-1）。增强的非辐射衰变和许多其他二酸形成的物理后果主要归因于非平面大环扭曲。这两个H4 TPP 2+和H4 OEP 2+先前已被证明通过X射线晶体学采用鞍形构象，和溶液中的两个二元酸的扰动性质的大小与晶体中的平面性的偏差的程度相关。提出了一个模型来解释卟啉二酸的非辐射衰减行为，这是相关的非平面卟啉一般。该模型包括存在的衰变漏斗的S-1-（π，π *）-状态的能量表面上的平衡构象和其他最小的激活障碍分开。有人建议，这些漏斗涉及的配置，在该配置的势能面的基态和激发态的方法更接近比在平衡激发态结构（S）从稳态荧光发生。讨论了对相关核坐标的可能贡献。
The photophysical properties of the lowest excited singlet states, S-1(pi,pi*), of two porphyrin diacids have been investigated. The diacids are H4TPP2+ and H4OEP2+, the diprotonated forms of free base tetraphenylporphyrin (H2TPP) and octaethylporphyrin (H2OEP), respectively. Both diacids exhibit perturbed static and dynamic characteristics relative to the parent neutral complexes in solution at room temperature. These properties include enhanced yields of S-1 - S-0 radiationless deactivation (internal conversion), which increase from similar to0.1 for H2TPP and H2OEP to 0.4 for H4OEP2+ and 0.6 for H4TPP2+. The fluorescence lifetimes of both diacids are strongly temperature dependent, with an activation enthalpy of similar to 1400 cm(-1) for S-1-state deactivation. The enhanced nonradiative decays and many other photophysical consequences of diacid formation are attributed primarily to nonplanar macrocycle distortions. Both H4TPP2+ and H4OEP2+ have been shown previously by X-ray crystallography to adopt saddle-shaped conformations, and the magnitudes of the perturbed properties for the two diacids in solution correlate with the extent of the deviations from planarity in the crystals. A model is proposed to explain the nonradiative decay behavior of the porphyrin diacids that is relevant to nonplanar porphyrins in general. The model includes the existence of decay funnels on the S-1-(pi,pi*)- state energy surface that are separated from the equilibrium conformation and other minima by activation barriers. It is suggested that these funnels involve configurations at which the potential-energy surfaces of the ground and excited states approach more closely than at the equilibrium excited-state structure(s) from which steady-state fluorescence occurs. Possible contributions to the relevant nuclear coordinates are discussed.