作者:Naoki Yamada、Miki Hasegawa、Ken-ichi Kumagai、Shigendo Enomoto、Hiroaki Horiuchi、Tetsutaro Yoshinaga、Hiroshi Hiratsuka、Michio Kobayashi、Toshihiko Hoshi
DOI:10.1246/bcsj.78.1018
日期:2005.6
Time-resolved transient absorption spectra of photo-irradiated 2,2′-pyridil were measured in PVA films. The broad bands at 552 and ∼455 nm, appearing just after photo-excitation of 2,2′-pyridil, are assigned to the skewed triplet species. The triplet species changes into 1-hydroxy-2-oxo-1,2-di(2-pyridyl)ethyl (pyridoil) radical via the abstraction of a hydrogen atom from the solvent. The radical produced by the photo-irradiation of 2,2′-pyridil is confirmed to be the pyridoil radical from the measurement of the polarized absorption spectrum, with the aid of the stretched polymer film technique and MO calculations. The time-resolved transient absorption spectra of 2,2′-pyridil irradiated by a xenon flash lamp in a 1:1 (v/v) mixed solvent of methanol and ethanol show that the pyridoil radical further abstracts a hydrogen atom from the solvent to afford cis-enediol (cis-1,2-di(2-pyridyl)-1,2-ethenediol) and that cis-enediol is converted into trans-enediol (trans-1,2-di(2-pyridyl)-1,2-ethenediol). 2,2′-Pyridil shows a structured Tn ← T1 absorption spectrum in a 1:1 (v/v) mixed solvent of methylcyclohexane and 2-methylbutane, indicating that 2,2′-pyridil takes a planar structure in the lowest triplet excited state in a nonpolar medium.
在 PVA 薄膜中测量了光照射 2,2′-吡啶的时间分辨瞬时吸收光谱。2,2′-pyridil 光激发后在 552 nm 和 ∼455 nm 处出现的宽波段归属于偏斜的三重物。通过从溶剂中抽取一个氢原子,三重态物质转变为 1-hydroxy-2-oxo-1,2-di(2-pyridyl)ethyl (pyridoil) 自由基。借助拉伸聚合物薄膜技术和 MO 计算,通过测量偏振吸收光谱,确认了光照射 2,2′-吡啶产生的自由基就是吡啶oil 自由基。在氙闪光灯照射下,2,2′-吡啶在 1:1:1(v/v)的甲醇和乙醇混合溶剂中,用氙闪光灯照射 2,2′-吡啶鎓的时间分辨瞬时吸收光谱显示,吡啶鎓自由基进一步从溶剂中抽取一个氢原子,生成顺式-1,2-二(2-吡啶基)-1,2-乙烯基二醇,顺式-1,2-二(2-吡啶基)-1,2-乙烯基二醇转化为反式-1,2-二(2-吡啶基)-1,2-乙烯基二醇。在甲基环己烷和 2-甲基丁烷 1:1 (v/v) 混合溶剂中,2,2′-吡啶显示出 Tn ← T1 结构吸收光谱,表明 2,2′-吡啶在非极性介质中的最低三重激发态具有平面结构。