Using a Fluorescent 1-Methyl-4-(2-Pyren-1-Yl-Vinyl)-Pyridinium Iodide to Characterize Solvent Polarities

We used 1-methyl-4-(2-pyren-1-yl-vinyl)-pyridinium iodide, a pyridinium derivative fluorescent dye, as a solvatochromic and solvatofluorchromic probe to straightforwardly characterize the solvent polarity. The absorption and fluorescence spectra of 1-methyl-4-(2-pyren-1-yl-vinyl)-pyridinium iodide show a dramatic dependence on solvent polarities in the high-polar range. It exhibits two absorption peaks around 400 and 450 nm, as well as an emission maximum at 605 nm. Several parameters (ratio of the two absorption peaks, wavelength of the principal absorption peak, fluorescence signal, and ratio of fluorescence intensities excited at the two absorption bands) are linearly dependent on the solvent polarity–polarizability values. Strong correlations have been also obtained with the P' and P_y polarity scales with small deviations. Moreover, 1-methyl-4-(2-pyren-1-yl-vinyl)-pyridinium iodide possesses high fluorescence quantum yield (0.38–0.54) and relatively long lifetime (2.2–2.6 ns) in all studied organic solvents. All these optical properties make 1-methyl-4-(2-pyren-1-yl-vinyl)-pyridinium iodide a favorable probe to quantitatively characterize the solvent polarities in the high-polar range through a multiparametric approach.