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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Lowest Excited State of Oxovanadyl(IV) Tetraphenylporphyrin
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Lowest Excited State of Oxovanadyl(IV) Tetraphenylporphyrin

机译：氧杂钒（IV）四苯基卟啉的最低激发态

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摘要

The excited-state relaxation dynamics and pathways of oxovanadyl(IV) tetraphenylporphyrin (OV~(IV)TPP) have been investigated by nanosecond time-resolved and steady-state emission, transient absorption, and transient resonance Raman spectroscopies. At room temperature, the emission spectrum shows a single broad featureless band centered near 790 nm in noncoordinating solvents such as toluene and benzene and at 814 nm in tetrahydrofuran (THF), whereas at 77 K the emission bands in the same solvents exhibit blue-shifts to 745 and 784 nm, respectively. Furthermore, the emission decay time in benzene increases from 40 to 60 ns with a decrease in temperature from 323 to 268 K. In contrast, the decay time in THF is ca. 1 ns, which is almost independent of temperature. The energy separation between the tripdoublet state (~2T(π, π~*)) and the tripquartet one (~4T(π, π~*)) under the proposed relaxation scheme of photoexcited OV~(IV)TPP has been estimated to be ca. 500 cm~(-1) in benzene and toluene. The transient absorption spectra at room temperature denote a broad featureless absorption centered at around 480 nm with a ground-state bleaching at 555 nm. All the spectroscopic results including the transient Raman spectra led us to conclude that the electronic nature of the lowest excited state should be the tripquartet state (~4T(π, π~*)) at ambient temperature. The decay times for both photoinduced absorption and bleaching are similar and also in good accordance with the emission decay times as long as temperature and solvent are the same. The time-resolved emission spectra and wavelength dependent decay kinetics at 77 K reveal that the observed emission spectra apparently originate from three different emitting species. These observations are discussed in terms of postulating a quenching state (Q), which is thermally accessible from the tripdoublet state (~2T(π, π~*)) of OV~(IV)TPP at room temperature.
机译：通过纳秒级时间分辨和稳态发射，瞬态吸收和瞬态共振拉曼光谱研究了氧杂钒基（IV）四苯基卟啉（OV〜（IV）TPP）的激发态弛豫动力学和途径。在室温下，发射光谱在非配位溶剂（例如甲苯和苯）中在790 nm附近显示一个单一的宽无特征带，在四氢呋喃（THF）中在814 nm处显示，而在相同溶剂中在77 K时发射带显示出蓝移分别为745和784 nm。此外，苯的发射衰减时间从40 ns增加到60 ns，而温度从323 K下降到268K。相反，THF的衰减时间大约为30 ns。 1 ns，这几乎与温度无关。据估计，在拟议的光激发OV〜（IV）TPP弛豫方案下，三重态（〜2T（π，π〜*））和三重四态（〜4T（π，π〜*））之间的能量分离为大约在苯和甲苯中500 cm〜（-1）室温下的瞬态吸收光谱表示中心在480 nm附近的宽无特征吸收，基态漂白在555 nm。所有的光谱结果，包括瞬态拉曼光谱，都使我们得出结论，在环境温度下，最低激发态的电子性质应该是三重态（〜4T（π，π〜*））。只要温度和溶剂相同，光致吸收和漂白的衰减时间是相似的，并且也与发射衰减时间一致。时间分辨的发射光谱和与波长相关的衰减动力学在77 K下揭示，观察到的发射光谱显然源自三种不同的发射物种。这些假设是根据假定淬灭态（Q）来讨论的，该淬灭态在室温下可从OV〜（IV）TPP的三重态（〜2T（π，π〜*））进行热访问。

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