Gagliardi Christopher J, Wang Li, Dongare Prateek, Brennaman M Kyle, Papanikolas John M, Meyer Thomas J, Thompson David W
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290.
Institute of Environmental Science, Shanxi University, Taiyuan, Shanxi, China 030006.
Proc Natl Acad Sci U S A. 2016 Oct 4;113(40):11106-11109. doi: 10.1073/pnas.1611496113. Epub 2016 Sep 22.
The phenols 4-methylphenol, 4-methoxyphenol, and N-acetyl-tyrosine form hydrogen-bonded adducts with N-methyl-4, 4'-bipyridinium cation (MQ) in aqueous solution as evidenced by the appearance of low-energy, low-absorptivity features in UV-visible spectra. They are assigned to the known examples of optically induced, concerted electron-proton transfer, photoEPT. The results of ultrafast transient absorption measurements on the assembly MeOPhO-H---MQ are consistent with concerted EPT by the instantaneous appearance of spectral features for MeOPhO·---H-MQ in the transient spectra at the first observation time of 0.1 ps. The transient decays to MeOPhO-H---MQ in 2.5 ps, accompanied by the appearance of oscillations in the decay traces with a period of ∼1 ps, consistent with a vibrational coherence and relaxation from a higher υ(N-H) vibrational level or levels on the timescale for back EPT.
酚类物质4-甲基苯酚、4-甲氧基苯酚和N-乙酰基酪氨酸在水溶液中与N-甲基-4,4'-联吡啶鎓阳离子（MQ）形成氢键加合物，这在紫外可见光谱中表现为低能量、低吸收率特征。它们被归类为光诱导协同电子-质子转移（photoEPT）的已知实例。对组装体MeOPhO-H---MQ进行的超快瞬态吸收测量结果与协同EPT一致，即在0.1 ps的首次观测时间，瞬态光谱中出现了MeOPhO·---H-MQ的光谱特征。瞬态在2.5 ps内衰减至MeOPhO-H---MQ，同时衰减轨迹中出现周期约为1 ps的振荡，这与在反向EPT时间尺度上从较高υ(N-H)振动能级的振动相干和弛豫一致。
