Synthesis and photophysical properties of highly fluorescent 2-aryl-6-(aryleneethynylene)-1H-indoles

Nine novel 2-aryl-6-(aryleneethynylene)-1H-indoles were prepared by one pot Sonogashira cross-coupling in DMSO and fluoride promoted cyclization followed by N-alkylation. The photophysical properties of these compounds are described. Absorption and excitation spectra of these compounds were independent of the solvent polarity, while their emission spectra showed a pronounced dependence. Fluorescence quantum yields in solution were very high and decreased with solvent polarity; possible processes that account for excessive values of ? are discussed. Cyclic voltammetry studies indicate irreversible redox processes and DFT calculations suggest they occur in the indole segment.