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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Femtosecond fluorescence dynamics of porphyrin in solution and solid films: The effects of aggregation and interfacial electron transfer between porphyrin and TiO2
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Femtosecond fluorescence dynamics of porphyrin in solution and solid films: The effects of aggregation and interfacial electron transfer between porphyrin and TiO2

机译：溶液和固体膜中卟啉的飞秒荧光动力学：卟啉与TiO2之间的聚集和界面电子转移的影响

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摘要

The excited-state relaxation dynamics of a synthetic porphyrin, ZnCAPEBPP, in solution, coated on a glass substrate as solid films, mixed with PMMA and coated on a glass substrate as solid films, and sensitized on nanocrystalline TiO2 films were investigated by using femtosecond fluorescence up-conversion spectroscopy with excitation in the Soret band, S-2. We found that the S-2 -> S-1 electronic relaxation of ZnCAPEBPP in solution and on PMMA films occurs in 910 and 690 fs, respectively, but it becomes extremely rapid, < 100 fs, in solid films and TiO2 films due to formation of porphyrin aggregates. When probed in the S-1 state of porphyrin, the fluorescence transients of the solid films show a biphasic kinetic feature with the rapid and slow components decaying in 1.9 - 2.4 and 19 - 26 ps, respectively. The transients in ZnCAPEBPP/TiO2 films also feature two relaxation processes but they occur on different time scales, 100 - 300 fs and 0.8 - 4.1 ps, and contain a small offset. According to the variation of relaxation period as a function of molecular density on a TiO2 surface, we assigned the femtosecond component of the TiO2 films as due to indirect interfacial electron transfer through a phenylethynyl bridge attached to one of four meso positions of the porphyrin ring, and the picosecond component arising from intermolecular energy transfer among porphyrins. The observed variation of aggregate-induced relaxation periods between solid and TiO2 films is due mainly to aggregation of two types: J-type aggregation is dominant in the former case whereas H-type aggregation prevails in the latter case.
机译：飞秒荧光法研究了合成卟啉ZnCAPEBPP在溶液中，固溶在玻璃基体上，与PMMA混合，固溶在玻璃基体上，并在纳米晶TiO2膜上敏化后的激发态弛豫动力学。上转换光谱，在Soret波段S-2中激发。我们发现，ZnCAPEBPP在溶液中和在PMMA膜上的S-2-> S-1电子弛豫分别发生在910和690 fs处，但是由于形成，固体膜和TiO2膜中ZnCAPEBPP变得非常快，<100 fs。卟啉聚集体。当以卟啉的S-1状态进行探测时，固体膜的荧光瞬变表现出双相动力学特征，快速和慢速分量分别衰减1.9-2.4和19-26 ps。 ZnCAPEBPP / TiO2薄膜的瞬态还具有两个弛豫过程，但它们发生在不同的时间范围内，分别为100-300 fs和0.8-4.1 ps，并且偏移很小。根据弛豫期随TiO2表面分子密度变化的变化，我们将TiO2薄膜的飞秒分量归因于由于间接界面电子通过连接到卟啉环四个内消旋位置之一的苯基乙炔桥进行的界面转移，皮秒成分是由卟啉之间的分子间能量转移引起的。固体和TiO2薄膜之间观察到的聚集体诱导的弛豫时间变化主要是由于两种类型的聚集：在前一种情况下J型聚集占主导，而在后者情况下H型聚集占主导。

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