ELECTRONIC SPECTRAL STUDIES AND DETERMINATION OF THE FIRST EXCITED SINGLET-STATE DIPOLE-MOMENTS OF NEW BENZO[A]PHENOTHIAZINE DERIVATIVES

The room temperature (298 K) electronic absorption, and fluorescence excitation and emission spectra of seven new, pharmacologically-important benzo[a]phenothiazines (12H-benzo[a]phenothiazine (1), 9-methyl-12H-benzo[a] phenothiazine (2), 10-methyl-12H-benzo[a] phenothiazine (3), 11-methyl-12H-benzo[a]phenothiazine (4), 5-oxo-5H-benzo[a]phenothiazine (5), 6-hydroxy-5oxo-5H-benzo[a]phenothiazine (6) and 6-methyl-5-oxo-5H-benzo[a] phenothiazine (7).) were measured in several solvents of different polarities and hydrogen bonding abilities. In combination with the ground state dipole moments of these benzo[a]phenothiazines, the spectral data were used to determine their first excited singlet-state dipole moments by means of the solvatochromic shift method. These excited singlet-state dipole moments were found to be significantly higher (1.9 to 2.5 Debye units) than their ground-state counterparts.