Absorption and Fluorescence Spectra of Anthracenecarboxylic Acids. I. 9-Anthroic Acid and Formation of Excimer

The absorption spectra of 9-anthroic acid (9-anthracenecarboxylic acid) in ethanol have been measured as a function of solute concentration. It was revealed that 9-anthroic acid forms a hydrogen-bonded dimer. The equilibrium constant for dimer formation was determined to be 6.6×104 mol−1 1 in ethanol at 298 K. The fluorescence spectra of 9-anthroic acid have been investigated as a function of concentration and temperature in various solvents. An excimer mechanism was proposed for a broad fluorescence of 9-anthroic acid; the hydrogen-bonded dimer is excited and then associates with an unexcited hydrogen-bonded dimer to form an excited tetramer from which the broad fluorescence occurs.