Novel Imidazole based Azo dyes as new chemosensors

Abstract

Azo dyes account for 60–70% of all dyes produced in the world. They are the most dominant artificially synthesized dyes that are widely used in various types of industries such as ink, paper, leather, plastic, textiles, food additives, therapeutic agents etc. Azobenzenes have been targeted for potential applications in areas of electronics, drug delivery, nonlinear optics, optical storage media, chemosensors, liquid crystals, photochemical molecular switches, molecular shuttles, nanotubes and in the manufacture of protective eye glasses and filters. A major challenge of their interest in this area is the development of chromophores with characteristics like high chemical stability, thermal stability over a wide temperature range and having two forms easily detectable by a method that does not cause irreversible molecular alterations. 1,2 In contrast to azobenzenes, heterocyclic azo compounds are less well investigated, although they have shown brilliant color and chromophoric strength.2

Here we report novel heterocyclic azo compounds with interesting photochemical properties. In a recent work, novel imidazole azo dyes were prepared in mild reaction conditions through an efficient method. All the products were isolated as dark red solids and their structures were assigned on the basis of 1H, 13C and 2D NMR and IR spectroscopy. These solids exhibited visual color changes in acid and basic solutions ranging from deep blue, to brilliant red colors. Solvatochromic effects were also observed in a series of polar and non-polar solvents. These visual changes were further studied by UV-Visible and NMR spectroscopy to investigate the photochemical behavior of these new molecules. Photochemical properties observed could be rationalized on the basis of the cis-trans isomerism and tautomeric equilibrium. These properties may found wide applications in various fields of science and technology, such as chemosensors and optical switches. Characterization data and photochemical properties of these novel imidazole based azo dyes will be presented and discussed.