Coumarin containing hetero[5/6]helical donor–acceptor molecules: Synthesis, photophysical properties and DFT studies

Coumarin containing hetero[5/6]helical derivatives with alkoxy substituent on coumarin ring were designed, synthesized and studied for their photophysical properties. Along with type of extended helical core around coumarin moiety, substitution on pendent aryl ring was also found to have significant effect on photophysical properties. Hetero [5]helical coumarin with furan ring in helical core and cyano substituted pendant aryl ring, compound 20a exhibited good quantum yield with blue fluorescence in both solid and solution state as compared to corresponding nitro analogue. For nitro substituted pendant aryl ring, phenanthrene moiety in helical core in compound 15b was found to play key role to show yellow fluorescence in hetero[6]helical coumarin. All the compounds were studied by DFT calculations for various structural as well as electronic parameters. TD-DFT calculations were studied for all the compounds to calculate various electronic parameters associated with excited state and correlated with the observed photophysical properties.