取代基和溶剂对4,4'-二取代二苯乙烯紫外吸收能量的影响

Effects of substituent and solvent on the UV absorption energy of 4,4'-disubstituted stilbenes

合成25个4,4'-二取代二苯乙烯化合物,测定了这些化合物在环己烷、乙醚、三氯甲烷、乙腈和醇等10多种溶剂中紫外吸收光谱的最大波长,共得到242个实验数据.讨论了取代基效应和溶剂效应对其紫外吸收光谱最大波长能量的影响.研究结果表明:同种溶剂中4,4′-二取代二苯乙烯化合物紫外吸收最大波长的能量主要受其分子内部结构(取代基效应)的影响,即由取代基的激发态参数σCexC和基态的极性参数σp共同决定;不同溶剂中其紫外吸收最大波长的能量由取代基效应和溶剂效应共同决定.提出了定量估算4,4′-二取代二苯乙烯化合物紫外吸收能量方程.并且发现,以溶剂在水/正辛醇中分配系数logP比用溶剂显色参数ET(30)度量溶剂效应更加有效,所得的定量方程相关性更好,物理意义更为明确.用所得方程对文献报道的有关化合物的紫外吸收光谱进行了预测,结果与实验测定值相吻合.

25 samples of 4,4＇-disubstituted stilbene derivatives were synthetised,and their UV absorption max wavelengths were determined in over 10 kinds of solvents including cyclohexane,ether,chloroform,acetonitrile and alcohol,in which 242 experimental data were recorded.The effects of substituents and solvents on the energy of their UV absorption max wavelengths were discussed.The reseach results showed：the energy of UV absorption max wavelengths of 4,4＇-disubstituted stilbenes was mainly affected by their intramolecular structure（substituent effect） in a given solvent,that is the energy is dominated by both of excited-state substituent parameter σ CexC and polar substituent constant σp.While their energy was dominated by the substituent effect and solvent effect in different kinds of solvents.An equation quantifying the energy of UV absorption max wavelengths of 4,4＇-disubstituted stilbenes was developed.In addition,it is found that the n-octanol/water partition coefficient（logP） is more effective than the solvatochromic dye（ET（30）） in scaling the solvent effect.The equation employing the parameter logP has a better correlation and more specific physical meaning.Further,the energies of UV absorption max wavelengths of some reported compounds were predicted by the obtained equation,which are in agreement with their experimental values.