Comparative Study of Azoxy-Based Liquid Crystals (p-azoxyanisole, pazoxyphenetole, ethyl-p-azoxybenzoate, ethyl-p-azoxycinnamate and n-octylp-azoxycinnamate) Based on Partial Atomic Charges

摘要

Computational study of electronic structure of some of azoxybenzene-based liquid crystals belonging to nematic class: p-azoxyanisole, p-azoxyphenetole, ethyl-p-azoxybenzoate, ethyl-p-azoxycinnamate and n-octyl-pazoxycinnamate have been studied. In order to obtain more information on the reactivity of above molecules towards nucleophile and electrophile, we performed semiempirical (AM1, PM3 and PM5) and density functional theory (DFT) based calculation to evaluate the negative and positive charge distribution in all the cases. p- Azoxyanisole is treated as reference compound (RC). The study shows that replacement of -OCH3 group of RC by - OC2H5 group increase the QMAX, while successive addition of –CH=CH-COOC8H17, –CH=CH-COOC2H5 and - COOC2H5 groups decreases the QMAX, respectively. In all the compounds it is the carbon atom at site 12, C12, which has QMAX, except in ethyl-p-azoxybenzoate, where QMAX is at C9. In respect to QMIN, it is the azoxy oxygen, O24, which has QMIN and the only differences in the trend is due to the positions of ethyl-p-azoxybenzoate and noctyl- p-azoxycinnamate, which are interchanged. The study also shows that DFT based calculations provide better result than the semiempirical based calculations