Experimental and Theoretical studies of 2-(2'-hydroxy-5'-methylphenyl)benzotriazole Derivatives modified at C-5' position with carbonyl groups

Abstract

A variety of novel UV absorbers modified at the C5’ position have been synthesized based on the theoretical calculations including optimized molecular structures predicted electronic and vibrational spectra (UV-Vis and IR spectra) In order to explain the experimental UV spectra chloroform solvent effect was introduced into calculation with Integral Equation Formalism Polarizable Continuum Model (IEFPCM) to create an environment more close to that of the real experimental In addition different combinations of theoretical calculation basis-sets were employed and tried to obtain the best results which well fit to our experimental results And it was found that B3LYP/6-311+G(d p) was the best calculation level with more reliable results and relatively low computing cost Among our target molecules compound 3 modified with carboxyl group at C-5' position showed the best UV-A (315 - 400 nm) and UV-C (200 - 280 nm) absorption ability; while compound 1 modified with formyl group at C-5' position showed the best UV-B (280 - 315 nm) absorption ability The comparison of UV spectra of compounds 1 with that of compound 6 indicated that the enhancement of UV-A range absorption is due to the strengthening of intramolecular hydrogen bond (IMHB) effect It also found that the comparison of UV spectra between compound 1 and 2 indicated that the enhancements of UV-B UV-C range absorption are due to the extension of the conjugation systems at C5’ position Theoretical calculated and experimental FT-IR spectra were used to ascertain that the IMHB of our target molecules were more strengthening compared to that Tinuvip P This was observed that the OH bonding stretching wavenumber of the experimental result was red-shifted indicating the IMHB between N1 and C2-OH became stronger This could be explain by the calculation results showing there was a hyperconjugative charge transfer from the lone pair of N atom to OH ?* bonding orbital as to result in decreasing the OH bond energy This results not only corresponded with the UV-A range absorption spectra but also corresponded with the H1-NMR spectra in which the OH peak was shifted to more down-field The calculation results showed that the enol form was favored for compound with IMBH and trans-keto form was favored for compounds with IMHB and modified at C5’ with carbonyl group The comparisons between experiment and calculation results showed that the UV-C absorption was mainly due to the existence of trans-keto from and the UV-A was mainly due to the existence of enol form Optical molecular orbitals calculation showed that UV-A absorption was due the electron transfer from the hydroxyphenyl moiety to benzotriazole moiety; while the UV-B and UV-C absorptions were due to the electron transfer from the hydroxylphenyl moiety to the C5’ carbonyl group

Date of Award	2016 Aug 11
Original language	English
Supervisor	Fu-Yung Huang (Supervisor)