Synthesis and fluorosolvatochromic properties of 1,7-annulated indoles

A new family of indole-based fluorescent dyes has been easily synthesized from readily available substrates. The structures of all new compounds were confirmed by NMR, IR, and HRMS and a crystallographic structure has been obtained for the 2,6-dicyanoaniline derivative 3. UV/vis absorption and photoluminescence spectroscopy analyses were performed on push-pull indole derivatives 1, 2 and 4. While the absorption maxima were almost independent of the solvent, the emission energy decreased while increasing the solvent polarity. A linear correlation between the orientation polarizability (Delta f) of the solvent and the Stokes shifts was observed and DFT calculations were carried out to study the influence of the planarity of the structures on the fluorescent quantum yields