Desingn, synthesis and photoinduced behaviour of pi - conjugated substrates: Aggregates and self - assemblies

Abstract

p-Conjugated substrates containing donor and/or acceptor substituents gained tremendous attention because of their wide applicability in materials to biology. Several variants of such pconjugated aryl and heteroaryl derivatives were designed, synthesized and investigated for their photoresponsive behavior. In this work, we have synthesized a series of donor (dimethylamine, triphenylamine, carbazole) or acceptor (nitro, cyano, isoxazole) substituted aryl polyenes and examined their fluorescence response in organic solvents and in heterogeneous media of micelles and sodium cholate. Upon substituting, a cyano group on the double bond, remarkably enhanced emission characteristics was observed in aqueous media. This emission is attributed to the formation of aggregates and this phenomenon is generally known as Aggregation Induced Enhanced Emission (AIEE). Such aqueous media emission response is used in determining critical micelle concentration (CMC) of the surfactants and to study pH sensitivity. Cholesterol tethered substrates containing dimethylamino donor and nitro acceptor result in large solvatochromic emission changes while presence of the cyano group on the double bond result in formation of nano structural assemblies. These cholesterol conjugates have been utilized to probe the changes in bile salts and surfactant assemblies. In presence of bile salts, cyano substituted stilbene and its cholesterol conjugates have exhibited nanostructures. The p-conjugated systems can find greater applications in their polymeric state compared to their monomeric form as many of the physical properties will improve. Therefore, to address this coumarin, thio coumarin and naphtho coumarin monomer derivatives have been synthesized and the optical properties have been examined. Polymers of the conjugated systems containing coumarin have been synthesized by step growth polymerization techniques and subsequent formation of photodimersis investigated.