Dipicolylamine styryldiazine derivatives: Synthesis and photophysical studies

International audienceDifferent D-π-A push-pull mols. in which dipicolylamine (DPA) is used as the donor group, different diazines as the acceptor groups, and styryl as the π-conjugated spacer have been synthesized in a straightforward manner by aldol condensation of 4-(di-2-picolylamino)benzaldehyde and the appropriate methyldiazine. All of the compds. showed π-π* transitions in the UV or visible region and the emission of yellow-green light upon irradn. Significant red shifts were obsd. in the fluorescence emission maxima of these compds. on increasing the solvent polarity, a finding that suggests the formation of an intramol. charge-sepd. emitting state that is also supported by semi-empirical calcns. In some cases, protonation led to marked color changes, thus showing the ability of these mols. to function as colorimetric pH sensors. The DPA and diazine units can act as coordination sites for metal cations such as Zn2+, Cd2+ or Hg2+, leading to a blue or red shift in the fluorescence spectra due to the change in the intramol. charge transfer properties. This phenomenon could become a powerful tool for the creation of multiple emission colors with a single mol. after suitable design