Influence Of Hydroxyl On The UV Spectra Properties,NMR And Reduction Potential Of Diaryl Schiff Base

In this paper, 69 Schiff base model compounds containing hydroxyl which can be divided intn three groups were synthesized.The first group is4-HOAr CH=NAr-Y^XAr CH=NAr OH-4’（4-HOBAY^XBAOH-4’）, the second group is 2-HOAr CH=NAr-Y^XAr CH=NAr OH-2’（2-HOBAY^XBAOH-2’）,and the third group is 3-HOAr CH=NAr-Y（3-HOBAY）. Their molecular structures has been characterized and confirmed. The data of UV absorption,NMR chemical shifts and ORP were obtained by measurement. The quantitative correlation analysis was carried out on the variation of the above properties, and compared with the corresponding properties of the similar compounds reported. The main contents are as follows:The energy of UV _maximum absorption wavelength λ_max（nm）(wave number :n_maxcm-1) about groupⅠand Ⅱ 57 kinds of model compounds was conducted for the quantitative correlation analysis, and the quantitative correlation equation with good reliability was obtained. We observed the hydroxyl have abnormal effects onλ_max. Compared with the n_max of XBAYs, 4-OH and 2-OH have a similar effect on the influence of n_max to the substituent X and Y of XBAYs. But 4’-OH causing a red-shife and 2’-OH causing a blue-shift have an “abnormal” effect on n_max. Besides,2-OH and 2’-OH have the Ortho steric effect, and caused a red-shift to n_max. These results provide important theoretical references for the molecular design of Schiff base compounds as optical materials.Comparison of ¹³C NMR of C=N bond chemical shifts δ_c（C=N） in groupⅠandⅡwith that in XAr CH=NAr Y was carried out, and get a good quantitative correlation equation. The results shows that the substituent has different influence to taeget compound and XAr CH=NAr Y. The δ_C（C=N） of 4-HOBAY 、 XBAOH-4 are affected by four main factors: the inductive effect parameter and conjugate effect parameters of X,the substituent specific cross-interaction effects between X and Y,and the impact of hydroxyl groups. And hydroxyl groups at different position in the C=N bridge have different impact on δ_C（C=N）. Although the conjugation of X is small,but it is useful to predict the compounds’ δ_C（C=N）precisely. Comparing ¹³C NMR of C=N bond chemical shifts of 2-HOBAY with that of XBAOH-2, we know that the factors affecting these two types of compounds are diffirent. There are threeprimary factors affecting the δ_c（C=N） of 2-HOBAY, they are the conjugated effect of Y,the excited-state substituent of Y, the interaction between ground state substituents X and Y, respectively. Also, there are three primary factors affect the δ_c（C=N） of XBAOH-2, they are the inductive effect of X, the excited-state substituent of Y and the interaction between ground state substituents X and Y, respectively. While excited states substituent parameters have little effect on the values of δ_c（C=N） it has certain effect in the precise calculation of δ_C（C=N）. The δ_C（C=N） value of 2-HOBAY is generally higher than that of XBAOH- 2’.The reduction potential（E（Red）） of 28 kinds of base model compounds（4- HOBAY XBAOH-4’）are determined. The OH has an additional effect on E（Red）, and causes the E（Red） decreasing by a constant. Then we induced and sumed up a equation for the quantification of E（Red） of mono/di-substituted XBAYs which has a good reliability.The UV-absorption _maximum wavelength(λ_max) of 12 kinds of model compounds 3-HOBAY are determined. n_max(cm-1, n_max =1/λ_max) was put into the quantitative correlation equation of literature reports. computer was used for data fitting, The obtaining value of OH is 0.47. The value can be trusted,comparing with λ_max of calculated value and experimental value. It can be used in the ultraviolet spectrum of organic compounds, performance and related optical molecular design.