Fluorescence of substituted pyrrolyl pyridines

The absorbance and fluorescence of 2-(1-pyrrolyl)-pyridine and three methylated derivatives have been studied in a variety of solvents. Absorbance spectra of the molecules were found to exhibit minor solvent dependence. The fluorescence spectra for all derivatives, however, show large red shifts in more polar solvents. Dual fluorescence has also been observed, consistent with locally excited and twisted intramolecular charge transfer (TICT) emission. Fluorescence intensity was also found to diminish in more polar solvents, consistent with a twisted excited state geometry for these molecules. The position and number of methyl substituents were found to affect the degree of charge-transfer emission. Quantum mechanical density functional calculations of ground state and vertical transition energies are presented to describe observed spectral behavior. Calculations include bulk solvation effects.