Luminescence of the Carboxyl Group

Abstract

A luminescence is observed from formic and acetic acids, their salts and esters. The yield of this luminescence is low $\text{(Φ\hspace{0.17em}<\hspace{0.17em}0.01)}$ . On the basis of much circumstantial evidence, we assign this emission as a ${}^3{\Gamma }_{\mathrm{\pi ,\pi *}}{\mathrm{\hspace{0.17em}\to \hspace{0.17em}}}^1{\Gamma }_1$ process located on the carboxyl group. Theoretical considerations are in reasonable accord with this conclusion when it is assumed that the ${}^3{\Gamma }_{\mathrm{\pi ,\pi *}}$ state geometry is considerably different from that of ${}^1{\Gamma }_1$ . Absorption spectroscopy indicates the presence of two low‐energy transitions in the formate ion; these absorption bands are quite weak and are assigned as two almost‐degenerate ${}^1{\Gamma }_{\mathrm{n,\pi *}}{\mathrm{\hspace{0.17em}\to \hspace{0.17em}}}^1{\Gamma }_1$ transitions of the formate ion.