Spectral studies of 9, 1 and 2-methyl anthroate and 2-anthroic acid

The substitution of a carboxyl group on the 9, 1 and 2-positions of anthracene produces several interesting changes in the characteristic spectral properties of the parent molecule. The absorption and fluorescence spectra, and fluorescence quantum yields of these carboxyl substituted anthracene compounds proved to be very solvent and position dependent. These spectra, quantum yields and related fluorescence lifetime data were used to determine the geometry of the ground and excited states for all three molecules. In the 9-position, molecular models and spectral evidence show that the plane of the carboxyl group is perpendicular to the plane of the ring in the ground state. In the excited state, the carboxyl group can rotate into a coplanar conformation with the ring enhancing the electronic interaction between the substituent and the ring (2). IN THE 2-position, the carboxyl group can assume a wide range of conformers centered around a coplanar configuration. Spectral evidence suggests that the range of conformers is more restricted in the excited state. In the l-position, molecular models and spectral evidence indicate that the carboxyl group can achieve a nearly coplanar configuration in the ground and excited states. The effects of carboxyl group substitution on the characteristic electronic transitions of anthracene were studied. In the 2-position, it was anticipated that the carboxyl group might have a large effect upon the weak Lb transition is found with carboxyl substitution on the 9, 2 or l-position. Several topics related to the main investigation of 9, 2 and l-methyl anthroate were studied. A comparison of the spectral properties of 2-methyl anthroate and 2-anthroic acid was made. A study of the effects of solvent polarity upon the fluorescence quantum yields an excited state energy of 2-methyl anthroate was performed. Empirically developed, experimental procedures are also discussed