Photoinduced charge separation of phenothiazine derivatives in layered zirconium phosphate at room temperature
作者:R M. Krishna、Vadim Kurshev、Larry Kevan
DOI:10.1039/a901801h
日期:——
The photoionization of alkylphenothiazines in layered α-zirconium phosphate (α-ZrP or ZrP) has been studied by electron spin resonance (ESR) and diffuse reflectance spectroscopies. Alkylphenothiazines (PCn where n=1, 2, 3, 4, 6, 8, 10, 16) were synthesized and used to study the effects of the alkyl chain length. Phenothiazine and N-alkylphenothiazines were incorporated into ZrP by impregnation and ion-exchange methods. By both methods N-alkylphenothiazines are only incorporated onto the external surface of zirconium phosphate rather than into the interlayer space. The alkylphenothiazines photooxidize at room temperature to form stable alkylphenothiazine cation radicals (PCn+) which are measured by ESR and diffuse reflectance. The framework of ZrP is suggested to be the electron acceptor. Both the photoyield and the decay rate of the alkylphenothiazine cation radical depend on the alkyl chain length. As the alkyl chain length of the PCn+ cation radical increases from methyl to hexyl, the photooxidation yield increases; and as the alkyl chain length increases further from hexyl to hexadecyl, the photooxidation yield decreases. However, the decay rate of the PCn+ cation radical gradually increases from methyl to hexadecyl which is explained in terms of a greater inductive effect for longer alkyl chains on the PCn+ cation radicals. Also, the resolution of the ESR spectrum decreases with increasing alkyl chain length which is interpreted as being due to decreasing mobility of the radical which should also decrease the decay rate. Both impregnation and ion-exchange methods are reasonably effective for incorporating alkylphenothiazine molecules into ZrP for efficient photooxidation. The photoyields of N-alkylphenothiazines in ZrP are larger than in silica gel which suggests that ZrP assemblies can be utilized for solar energy conversion and storage.
通过电子自旋共振(ESR)和漫反射光谱研究了烷基吩噻嗪类化合物在层状α-磷酸锆(α-ZrP 或 ZrP)中的光离子化。合成了烷基吩噻嗪(PCn,n=1、2、3、4、6、8、10、16),并用于研究烷基链长度的影响。吩噻嗪和 N-烷基吩噻嗪通过浸渍法和离子交换法加入到 ZrP 中。通过这两种方法,N-烷基吩噻嗪只被加入到磷酸锆的外表面,而不是层间空间。烷基吩噻嗪在室温下发生光氧化反应,形成稳定的烷基吩噻嗪阳离子自由基(PCn+),并通过 ESR 和漫反射进行测量。ZrP 的框架被认为是电子受体。烷基吩噻嗪阳离子自由基的光产率和衰减率都取决于烷基链的长度。当 PCn+ 阳离子自由基的烷基链长度从甲基增加到十六烷基时,光氧化产率增加;当烷基链长度从十六烷基进一步增加到十六烷基时,光氧化产率降低。然而,从甲基到十六烷基,PCn+阳离子自由基的衰减率逐渐增加,这是因为较长的烷基链对 PCn+阳离子自由基的感应效应更大。此外,随着烷基链长度的增加,ESR 光谱的分辨率也会降低,这是因为自由基的流动性降低,衰减速率也会降低。浸渍法和离子交换法对于将烷基吩噻嗪分子加入 ZrP 以实现高效光氧化都相当有效。ZrP 中 N-烷基吩噻嗪的光产率大于硅胶中的光产率,这表明 ZrP 组件可用于太阳能转换和储存。