Optical properties of new fluorescent iminocoumarins: Part 1

The optical properties of 10 new iminocoumarin dyes, bearing a cyano group at the 3-position, were studied in CH2Cl2 by UV/vis absorption and fluorescence spectroscopy. Five of the dyes bear a free imino group, and differ by the nature and position of their electron-donor group. Among them, the dye bearing a diethylamino group at the 7-position displayed the most interesting optical properties. All the compounds were compared to analogues containing an ethoxycarbonyl group on the imino function. The presence of the ethoxycarbonyl group systematically induced a shift of the absorption and emission spectra towards long wavelengths. For the three dyes where charge transfer is weak, substitution reduced fluorescence efficiency. In contrast, the fluorescence quantum yield and lifetime were slightly increased for the compounds with strong charge transfer, and especially for that bearing a diethylamino group at the 7-position. This shows that substitution on the imino group can be a convenient way to obtain good fluorescent probes designed for various purposes. (c) 2006 Elsevier Ltd. All rights reserved.