A SOLVATOCHROMIC STUDY OF NEW BENZO[A]PHENOTHIAZINES FOR THE DETERMINATION OF DIPOLE-MOMENTS AND SPECIFIC SOLUTE-SOLVENT INTERACTIONS IN THE FIRST EXCITED SINGLET-STATE
Jj. Aaron et al., A SOLVATOCHROMIC STUDY OF NEW BENZO[A]PHENOTHIAZINES FOR THE DETERMINATION OF DIPOLE-MOMENTS AND SPECIFIC SOLUTE-SOLVENT INTERACTIONS IN THE FIRST EXCITED SINGLET-STATE, Journal of photochemistry and photobiology. A, Chemistry, 101(2-3), 1996, pp. 127-136
The electronic absorption and fluorescence excitation and emission spe
ctra of seven benzo[a]phenothiazines, including 12H-benzo[a]phenothiaz
ine, 9-methyl-benzo[a]phenothiazine, 10-methyl-benzo[a]phenothiazine,
11-methyl-benzo[a]phenothiazine, 5-oxo-5H-benzo[a]phenothiazine, 5-oxo
-6-methyl-benzo[a]phenothiazine and 5-oxo-6-hydroxy-benzo[a]phenothiaz
ine, were determined at room temperature (298 K) in solvents of variou
s polarity (cyclohexane, ethyl ether, ethyl acetate, tetrahydrofuran,
ethanol, dimethylformamide, acetonitrile and dimethylsulphoxide). The
effect of the solvent on the spectral characteristics was studied quan
titatively. In combination with the ground state dipole moments of the
se compounds, the spectral data of the benzo[a]phenothiazines were use
d to evaluate their first excited singlet state dipole moments using t
he solvatochromic shift method (Bakhshiev and Kawski-Chamma-Viallet co
rrelations). The theoretical ground and excited singlet state dipole m
oments of the benzo[a]phenothiazines were also calculated as the vecto
r sum of the pi component (obtained by the Pariser-Parr-Pople method)
and the sigma component (obtained from sigma bond moments). In most ca
ses, a satisfactory agreement was found between the experimental and c
alculated values of the dipole moments. For most benzo[a]phenothiazine
derivatives under study, the experimental excited singlet state dipol
e moments were higher than their ground state counterparts. The applic
ation of the Kamlet-Abboud-Taft solvatochromic parameters to explain t
he effect of the solvent on the spectral properties of benzo[a]phenoth
iazines is discussed.