New push-pull type dendritic stilbazolium dyes: synthesis, photophysical and electrochemical investigation

The synthesis of some dendritic tri- and tetra-chromophoric solvatochromic stilbazolium dyes is presented. The dyes were characterized by H-1, C-13 NMR and mass spectroscopy. The UV Vis and steady-state fluorescence spectroscopic investigation shows a solvatochromic absorption and emission, which result from the intramolecular charge transfer (ICT) nature of the chromophores present in the dendritic structure (1-4). The fluorescence decay was fitted to bi-exponential in all the solvents. Systematic variation of fluorescence quantum yield and lifetime in organic solvents were observed. In chloroform and dichloromethane, these dyes show intense fluorescence and the fluorescence lifetime is also high, which is due to specific interaction of the dye with solvent. Using cyclic voltammetry (CV) experiments, the electrochemical response of the dyes and electronic interactions between the electroactive sites of these dendritic constructs were explored. CV responses of these dyes (3, 4a and 4b) show three successive, well-separated reduction peaks, which indicate strong electronic coupling between the chromophoric units. (C) 2004 Elsevier Ltd. All rights reserved.