B. I. Stepanov Institute of Physics of National Academy of Sciences, Pr. Nezavisimosti 68, Minsk 220072, Belarus.
J Phys Chem A. 2012 Nov 8;116(44):10695-703. doi: 10.1021/jp305326x. Epub 2012 Sep 27.
The fluorescence spectra of 10-(4,6-dichloropyrimidin-5-yl)-5,15-dimesitylcorrole have been studied in the temperature range from 4.2 to 332 K. For the first time, the individual fluorescence profiles of the two corrole NH tautomers have been assigned over the whole temperature range. The pronounced temperature dependence of the fluorescence spectra of the meso-pyrimidinylcorrole under study was found to originate from switching between the fluorescence emissions of the two tautomers due to a reduced NH tautomerization rate with decreasing temperature. As a result, the long wavelength tautomer dominates the total emission spectrum at room temperature, whereas at low temperatures, the majority of the emission comes from the short wavelength tautomer. Energy level diagrams (involving the two NH tautomers) explaining the excitation energy deactivation channels in the meso-pyrimidinylcorrole at room temperature and below are presented. A significant H/D isotope effect on the NH tautomerization rate has been observed, resulting in an enhanced contribution of the short wavelength tautomer to the total fluorescence spectrum at the expense of that of the long wavelength tautomer. Substantially different fluorescence quantum yields have been determined for the individual NH tautomers, leading to a pronounced temperature dependence of the overall fluorescence quantum yield. The obtained results allow the unambiguous statement that the two NH tautomers of corroles coexist in fluid and solid solutions in a wide range of temperatures, with the proportion depending on the corrole substitution pattern. Moreover, this study shows that the (future) interpretation of the fluorescence properties of meso-pyrimidinylcorroles and all other corrole materials should be done (more) carefully, taking into account the coexistence of NH tautomers with individual spectral signatures.
10-（4,6-二氯嘧啶-5-基）-5,15-二-间二甲苯基卟啉的荧光光谱在 4.2 至 332 K 的温度范围内进行了研究。首次在整个温度范围内分配了两个卟啉 NH 互变异构体的个别荧光轮廓。研究中发现，所研究的间嘧啶基卟啉的荧光光谱具有明显的温度依赖性，这是由于随着温度的降低，NH 互变异构体的速率降低，两种互变异构体的荧光发射之间发生了转换。结果，在室温下，长波长互变异构体主导总发射光谱，而在低温下，大多数发射来自短波长互变异构体。提出了（涉及两个 NH 互变异构体）解释室温下和室温以下间嘧啶基卟啉中激发能失活通道的能级图。观察到 NH 互变异构体速率对 H/D 同位素效应显著，导致短波长互变异构体对总荧光光谱的贡献增加，而长波长互变异构体的贡献减少。已确定单个 NH 互变异构体的荧光量子产率有很大差异，导致总荧光量子产率的明显温度依赖性。所获得的结果使得可以明确声明，在很宽的温度范围内，卟啉的两个 NH 互变异构体共存于流体和固体溶液中，其比例取决于卟啉的取代模式。此外，这项研究表明，（未来）对间嘧啶基卟啉和所有其他卟啉材料的荧光性质的解释应该（更）小心，考虑到具有个别光谱特征的 NH 互变异构体的共存。
