2-甲基-1-硝基萘激发态分子内氢转移的瞬态吸收光谱及其理论计算研究

Investigation on Nanosecond Transient Absorption Spectroscopy and Theoretical Calculation of Excited-state Intramolecular Hydrogen Transfer of 2-Methyl-1-Nitronaphthalene

利用纳秒瞬态吸收光谱技术和密度泛函理论(DFT)、完全活化空间自洽场(CASSCF)等计算方法,研究了2-甲基-1-硝基萘(2M1NN)在有机溶剂中的激发态分子内氢转移反应。通过实验获得了2M1NN的瞬态吸收光谱和动力学常数,400nm处拟合得到3个衰减时间常数,其中25μs的物种指认为三重态分子内氢转移后生成的顺式硝酸亚基中间体。实验获得二茂铁猝灭三重态2M1NN的速率常数为1.77×1010 mol-1·dm3·s-1。理论计算预测了可能的氢转移通道,推测分子内氢转移的机理为三重态2M1NN发生分子内氢转移生成双自由基中间体,再系间窜越生成硝酸亚基中间体。

Excited-state intramolecular hydrogen transfer of 2-Methyl-1-Nitronaphthalene（2M1NN）in organic solvent was investigated by nanosecond transient absorption spectroscopy,Density Functional Theory（DFT）and complete a ctive space self-consistent field（CASSCF）.Transient absorption spectra and kinetic constants of 2M1 NN were obtained,and 3decay time constants were gained at 400 nm,in which the 25μs component was assigned to the intermediate of Z-aci-nitro isomer after intramolecular hydrogen transfer.The second-order quenching rate constant of 2M1 NN triplet by ferrocene is 1.77×1010mol-1·dm3·s-1.The results of theoretical calculations and transient absorption experiments predicted the possible hydrogen transfer mechanism,and indicated intramolecular hydrogen transfer takes place at the lowest triplet state of 2M1 NN,forming biradical species,then undergoing intersystem corssing.