Direct Observation of Transient Species Generated from Protonation and Deprotonation of the Lowest Triplet of p-Nitrophenylphenol  

4-硝基联苯酚三重态质子化和去质子化过程中瞬态物种的指认

作　　者：Jing Long Zhao Ye Yong Du Xu-ming Zheng Jia-dan Xue 龙静;叶昭;杜勇;郑旭明;薛佳丹(浙江理工大学化学系,杭州310018;中国计量大学太赫兹研究中心,杭州310018)

机构地区：[1]Department of Chemistry,Zhejiang Sci-Tech University,Hangzhou 310018,China [2]Centre for THz Research,China Jiliang University,Hangzhou 310018,China

出　　处：《Chinese Journal of Chemical Physics》2020年第5期635-641,I0070-I0077,I0079,共16页化学物理学报（英文）

基　　金：supported by the National Natural Science Foundation of China(No.21973082)。

摘　　要：Photo-induced proton coupled electron transfer(PCET)is essential in the biological,photosynthesis,catalysis and solar energy conversion processes.Recently,p-nitrophenylphenol(HO-Bp-NO2)has been used as a model compound to study the photo-induced PCET mechanism by using ultrafast spectroscopy.In transient absorption spectra both singlet and triplet states were observed to exhibit PCET behavior upon laser excitation of HO-Bp-NO2.When we focused on the PCET in the triplet state,a new sharp band attracted us.This band was recorded upon excitation of HO-Bp-NO2 in aprotic polar solvents,and has not been observed for p-nitrobiphenyl which is without hydroxyl substitution.In order to find out what the new band represents,acidic solutions were used as an additional proton donor considering the acidity of HO-Bp-NO2.With the help of results in strong(~10^-1 mol/L)and weak(~10^-4 mol/L)acidic solutions,the new band is identified as open shell singlet O-Bp-NO2H,which is generated through protonation of nitro O in 3HO-Bp-NO2 followed by deprotonation of hydroxyl.Kinetics analysis indicates that the formation of radical·OBp-NO2 competes with O-Bp-NO2H in the way of concerted electron-proton transfer and/or proton followed electron transfers and is responsible for the low yield of O-Bp-NO2H.The results in the present work will make it clear how the3HO-Bp-NO2 deactivates in aprotic polar solvents and provide a solid benchmark for the deeply studying the PCET mechanism in triplets of analogous aromatic nitro compounds.

关 键 词：Proton coupled electron transfer Intramolecular charge transfer Transient absorption TRIPLET nitrophenylphenol 

分 类 号：O657.3[理学—分析化学] O643.1[理学—化学]