α,ω-Diphenylpolyenes cabable of exhibiting twisted intramolecular charge transfer fluorescence: a fluorescence and fluorescence probe study of nitro- and nitrocyano-substituted 1,4-diphenylbutadienes

Abstract

1,4-Diphenylbutadiene compounds, namely 1-p-cyanophenyl-4-phenylbuta-1E,3E-diene (2), 1-p-nitrophenyl-4-phenylbuta-1E,3E-diene (3), 1-cyano-1,4-diphenylbuta-1Z,3E-diene (4), 1-p-cyanophenyl-4-p-nitrophenylbuta-1E,3E-diene (5), 1-cyano-1-p-nitrophenyl-4-phenylbuta-1Z,3E-diene (6), and 1-cyano-1-phenyl-4-p-nitrophenylbuta-1Z,3E-diene (7), have been synthesized and their absorption and fluorescence properties in organic solvents, water-dioxane, and SDS, CTAB, and Triton-X-100 micelles have been investigated. The fluorescence behavior of these dienes has also been examined in ethanol-methanol (1:1) matrix at 298 and 77 K. The dienes with nitro substituents on the aromatic ring are capable of exhibiting dramatically red-shifted fluorescence emission due to twisted intramolecular charge-transfer excited states. The fluorescence properties of nitro-substituted dienes 3, and 5-7 have been utilized to probe the microenvironment of SDS and CTAB micelles in terms of dielectric constant of water-micelle interface, location of the probe molecules in the micelles, and the cmc values. This study has brought out interesting features of the excited state structure and potential energy surface of diphenylpolyenes. It further provides new directions for the development of fluorescence probes as sensors and reporters of microenvironments of organized assemblies.