A green and sustainable incorporation of bi- and ter-thiophenes into 1,4-dihydropyridines: synthetic, mechanistic and photophysical investigations

Bi- and ter-thiophene moieties have been incorporated into 1,4-dihydropyidines (DHPs) via a novel and green, solvent- free, one pot multi-component Hantzsch reaction. Effect of catalyst, solvents and temperature were studied to optimize the reaction condition. Tetra noctyl ammonium bromide (TOAB) was used as a promoter and trace amount of water inadvertently trapped in ammonium acetate acted as catalyst to facilitate the reaction. A combined experimental and quantum chemical mechanistic study was carried out to elucidate how only trace amount of water is central to the success of the proposed synthetic protocol, while bulk water actually inhibits the reaction. A combined experimental and quantum chemical photophysical study was carried out to assess the impact of conjugation extension for bi- and ter-thiophene DHPs compared to mono-thiophene DHP. It was found that the DHP moiety determined the photophysical behavior for monothiophene incorporated products, but the behavior of terthiophene incorporated DHPs reflected that of the corresponding thiophene moieties.