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Abnormal effect of hydroxyl on the longest wavelength maximum in ultraviolet absorption spectra for bis‐aryl Schiff bases
Authors:Chao‐Tun Cao  Wei Zhou  Chenzhong Cao
Affiliation:Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan Provincial University Key Laboratory of QSAR/QSPR, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan, Hunan Province, China
Abstract:Two sets of bis‐aryl Schiff bases that contain 4(or 4′)‐OH and 2(or 2′)‐OH were synthesized. The first set consists of 4‐HOArCH=NArY and XArCH=NArOH‐4′, and the second set consists of 2‐HOArCH=NArY and XArCH=NArOH‐2′. Their ultraviolet absorption spectra were measured and investigated. A very interesting phenomenon was observed by analyzing their wave number νmax (cm?1) of longest wavelength maximum λmax (nm) of ultraviolet. Compared with the change regularity of the νmax of XArCH=NArY (where the X and Y excluded OH), the 4′‐position hydroxyl (4′‐OH) and 2′‐position hydroxyl (2′‐OH) have abnormal performance. The details are the following: the 4′‐OH contributes an additional red shift to the νmax of XArCH=NArOH‐4′ (λmax increase), whereas the 2′‐OH contributes an additional blue shift to the νmax of XArCH=NArOH‐2′ (λmax decrease). In addition, there are ortho steric effects of all 2‐OH and 2′‐OH on the νmax for 2‐HOArCH=NArY and XArCH=NArOH‐2′, and the ortho steric effect contributes a red shift to their νmax. These experimental facts can provide an important theoretical reference for us using aryl Schiff base compounds as optical materials and performing the molecular design.
Keywords:hydroxyl  ortho steric effect  Schiff base  substituent effect  ultraviolet absorption spectra
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