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首页> 外文期刊>Bulletin of the Chemical Society of Japan >Vibrational Energy Relaxation of Metalloporphyrins in a Condensed Phase Probed by Time-Resolved Resonance Raman Spectroscopy
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Vibrational Energy Relaxation of Metalloporphyrins in a Condensed Phase Probed by Time-Resolved Resonance Raman Spectroscopy

机译：时间分辨共振拉曼光谱探测的凝聚相中金属卟啉的振动能弛豫

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摘要

Recent experimental work on vibrational energy relaxation of metalloporphyrins in a condensed phase carried out in this laboratory is summarized. The formation of a vibrationally excited photoproduct of metalloporphyrins upon (pi, pi~*) excitation and its subsequent vibrationl energy relaxation were monitored by picosedond time-resolved resonance Raman spectroscopy. Results related to intramolecular relaxation of octaethylporphyrinato nickel (NiOEP) are described. Stokes Raman bands due to a photoproduct of NiOEP istantaneously appeard upon the photoexcitation. Their intensities decayed with a time constant of approx 300 ps, which indicates an electronic relaxation from the (d,d) excited state (B_(1g)) to the ground state (A_(1g)), being consistent with the results of transient absorption measurements. Anti-Stokes v_4 and v_7 bands for vibrationally excited (d,d) state of NiOEP decayed with time constants of approx 10 and approx 300 ps. The former is ascribed to vibrational relaxation, while the latter corresponds to the electronic relaxation frome the (d,d) excited state to the electronic ground state. While the rise of anti-Stokes v_4 intensity was instrument-limited, the rise of anti-Stokes v_7 intensity was delayed by 2.0 +- 0.4 ps, which indicates that intramolecular vibrational energy redistribution has not been completed in the subpicosecond time regime. To study the mechanism of intermolecular energy transfer, solvent dependence of the time constants of anti-Stokes kinetics was investigated using various solvents. No significant solvent dependence of the rise and decay constants was observed for NiOEP. For an iron porphyrin, we observed two phases in intermolecular energy transfer. The fast phase was insensitive to solvent and the slow phase depended on solvents. A model of classical thermal diffusion qualitatively reproduced this behavior. For myoglobin, temporal changes of the anti-Stokes Raman intensity of the v_4 and v_7 bands demonstrated immediate generation of a vibrationally excited heme upon photodissociation and subsequent decays of the excited populations, whose time constants were 1.1 +- 0.6 and 1.9 +- 0.6 ps, respectively. This direct monitoring of the cooling dynamics of the the heme cofactor within the protein matrix allows the characterization of the vibrational energy flow through the protein moiety and to the water bath. For solute-solvent energy transfer process, low-frequency modes of proteins seem to be less important.
机译：总结了在该实验室中进行的金属卟啉在凝聚相中振动能弛豫的最新实验工作。通过皮秒级时间分辨共振拉曼光谱法监测（pi，pi *）激发时金属卟啉的振动激发光产物的形成及其随后的振动能弛豫。描述了与八乙基卟啉镍（NiOEP）的分子内弛豫有关的结果。由NiOEP的光产物引起的斯托克斯拉曼谱带在光激发时同时出现。它们的强度以约300 ps的时间常数衰减，这表明从（d，d）激发态（B_（1g））到基态（A_（1g））的电子弛豫，与瞬态结果一致吸收测量。 NiOEP的振动激发（d，d）状态的反斯托克斯v_4和v_7带以大约10 ps和大约300 ps的时间常数衰减。前者归因于振动弛豫，而后者对应于从（d，d）激发态到电子基态的电子弛豫。虽然抗斯托克斯v_4强度的升高受到仪器的限制，但抗斯托克斯v_7强度的升高被延迟了2.0±0.4 ps，这表明在皮秒以下时间范围内分子内振动能量的重新分配尚未完成。为了研究分子间能量转移的机理，使用各种溶剂研究了反斯托克斯动力学时间常数的溶剂依赖性。对于NiOEP，没有观察到明显的溶剂依赖性的上升和下降常数。对于卟啉铁，我们观察到分子间能量转移的两个阶段。快相对溶剂不敏感，慢相取决于溶剂。经典的热扩散模型定性地再现了这种行为。对于肌红蛋白，v_4和v_7谱带的反斯托克斯拉曼强度的时间变化表明，光解离后立即产生了振动激发的血红素，随后激发群体衰减，其时间常数分别为1.1 +-0.6和1.9 +-0.6 ps ， 分别。对蛋白质基质中血红素辅因子的冷却动力学的这种直接监测允许表征通过蛋白质部分并流至水浴的振动能。对于溶质-溶剂能量转移过程，蛋白质的低频模式似乎不太重要。

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