Synthesis of photochromic compounds has attracted much attention in the last two decades. Azobenzenes, a well known class of photochromic molecules, has the interesting property of photoisomerization of trans- and cis-isomers. The trans-to-tis isomerization happens efficiently upon exposure to light at an appropriate wavelength. The reverse cis-to-trans isomerization takes place by either irradiation with a different light wavelength or thermal relaxation. In this paper, three photochromic azobenzene-based tetradentate ligands have been synthesized and their photo-physical properties have been examined. The synthesis was started by preparation of 5-(Phenylazo) salicylaldehyde derivatives through diazotization of aniline derivatives followed by coupling them with salicylaldehyde in a basic medium. Three tetradentate Schiff bases have been obtained by treatment of 5-(Phenylazo) salicylaldehyde derivatives and 1,2-benzenediamine in (2:1) molar ratio respectively in methanol. Structure of the synthesized photochromic tetradentate ligands were confirmed by 1HNMR and IR spectroscopy. The ability of the synthesized Schiff bases to undergo trans-to-cis isomerization by light was examined using UV-vis spectroscopy. All three synthesized have showed efficient photoswitching ability. For example, the study of UV-vis spectrum of phenol,2,2'-[1,2-phenylene bis(nitromethylidyne)]bis[4-(phenylazo)], using in dichloromethane showed a strong band at a wavelength of 346 nm which is attributed to p-p* transition (for the most thermally stable trans isomer). Upon illumination with monochromic light 365 nm in 20 sec interval, a decrease in π−π* transition band was observed with a slight increase of n−π* band due to the conversion to cis isomers. The photo-stationary state has been reached after 2 minutes with 70% trans-to-cis conversion. The reverse cis-to-trans isomerization was achieved thermally and the complete conversion was confirmed by recovery of the original p-p* transition. The results confirmed that the synthesized compounds can undergo photoisomerization when exposed to irradiation at an appropriate wavelength.

Synthesis of novel photochromic azobenzene derivatives

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.