中文摘要：

基于密度泛函理论（DFT）中的B3LYP方法,在6-311＋＋G（d,p）水平上全优化得到了3,3′-偶氮苯磺酸（3,3′-AbS）在S0和T1态顺反异构化机理.在S0态存在两种异构化途径：绕角NNC反转和绕NC键旋转相结合的形式和单纯的绕CNNC二面角旋转形式,两种异构化途径的能垒分别为94.2和124.3kJ·mol^-1.有必要指出的是,在反转与旋转结合的途径上存在二次过渡态.在T1态上仅存在旋转途径且其能垒为21.1kJ·mol^-1.采用含时密度泛函理论（TD-DFT）,在B3LYP/6-311＋＋G（d,p）水平上,沿着基态的两种异构化途径计算得到了T1,S1,T2和S2态的垂直激发的势能剖面,分析了可能的光致异构化途径.当激发光波长为330nm时,反应物分子被激发到S2态,然后弛豫到较低的能态S1发生异构化反应,旋转途径存在两条活化途径：（1）沿着S1/S0的圆锥交叉点衰变到产物;（2）由S1态弛豫到T1态后,在S0-T1-S0的区域发生异构化,再转化到产物.计算结果表明,3,3′-AbS通过反转和旋转的结合形式实现在S0态的异构化,而被激发后倾向于沿着旋转坐标作为其主要的异构化途径.

英文摘要：

Photoisomerization pathways for 3,3＇-azobenzene sulfonate（3,3＇-AbS） in the S0 and T1 states were studied by using density functional theory（DFT） at the B3LYP/6-311＋＋G（d,p） level.In the S0 state,there are two isomerization pathways：the inversion of one NNC angle combined with the rotation around the NC bond and the rotation of the CNNC dihedral angle.The energy barriers of the two pathways are 94.2 and 124.3 kJ·mol-1,respectively.It is worthy to notice that there exist second-order transition states on the combination pathways of inversion and rotation.In the T1 state,only the rotation pathway exists and its energy barrier is 21.1 kJ·mol-1.To investigate the photoisomerization pathway,the potential energy profiles of the vertical excitation for the excited states（T1,S1,T2,and S2） were calculated by time dependent density functional theory（TD-DFT） at the B3LYP/6-311＋＋G（d,p） level along the two pathways.A photoexcitation at 330 nm results in the reactant molecule populating the S2 state and then undergoing a rapid relaxation to the minimum of the S1 state.Two possible isomerization pathways exist through the rotation pathway as follows：（1） the isomerization can easily occur through the S0/S1 conical intersection（CI） and descend to the S0 state;（2） a relaxation to the T1 state from the S1 state may occur and the reaction can take place via the S0-T1-S0 path.Calculation results show that the primary isomerization pathways for 3,3＇-AbS are a combination pathway of inversion and rotation in the S0 state and the rotation pathway when it is excited.