Amino substituted 4-pyridylbutadienes: Synthesis and fluorescence investigations

Synthesis and spectroscopic investigations of a series of donor-π-acceptor systems containing pyridine as the electron withdrawing group and an amino derivative (dimethylamino, diphenylamino, carbazole and julolidine) as electron donating group, separated by a π-spacer are described. The effect of varying donors on absorption and emission properties was studied in different solvents. All the molecules investigated exhibit pronounced positive polarity dependent solvatochromic shifts of up to ∼141 nm. Strong fluorescence quantum yields are also observed for dienes containing carbazole and diphenylamine donors. This behavior suggests the presence of highly polar emitting states as a result of π -π∗intramolecular charge-transfer (ICT). The observations were corroborated by a linear relation of the fluorescence maximum (ν<inf>max</inf>) versus the solvent polarity function (Δ<inf>f</inf>) from the Lippert-Mataga correlation. The emission lifetime shows a decay profile consistent with the formation of one species (1 and 3) and two species (2 and 4) in the excited state.