SOLVATOCHROMIC SPECTROSCOPY OF LUMINOL IN SOLVENT MIXTURES

The shift of the fluorescence band of luminol was measured in several polar and non-polar solvent mixtures. These shifts can be explained by the process of specific solvation known as dielectric enrichment. The dipole moment of excited molecules is obtained from the ratio between the solvent shifts of the absorption and fluorescence spectra; for the first excited singlet state of luminol the dipole moment is 6 D (compared with 2.5 D in the ground state). The displacement of the fluorescence band was also measured as a function of temperature to obtain the thermochromic shifts (4.9 cm-1 K-1 in methyltetrahydrofuran and 10.5 cm-1 K-1 in ethanol).