H. Gorner et al., EXCITED-STATE PROPERTIES OF 10-PHENYL-BENZO[B][1,6]NAPHTHYRIDINES IN SOLUTION, Journal of photochemistry and photobiology. A, Chemistry, 85(1-2), 1995, pp. 23-31
The relaxation pathways of excited 10-phenyl-benzo[b][1,6]naphthyridin
e (PN), an analogue of acridine, and a series of 12 derivatives (R-6:
CF3, Br, Cl, F, CH3, OCH3; R-8: SO2NH2, Br, Cl, CH3, OCH3, OC2H5) were
studied in several solvents at 297 and 77 K. Fluorescence, intersyste
m crossing and photodecomposition processes were examined by stationar
y and transient techniques. At 297 K, the quantum yield of fluorescenc
e (Phi(f)) increases significantly with solvent polarity and with elec
tron-donating substitution, intersystem crossing partly compensating t
his effect. The triplet is characterized by T-T absorption at 297 and
77 K and by phosphorescence at 77 K. Generally, intersystem crossing i
s less sensitive to environment and substitution than Phi(f). Photodec
omposition is negligible for PNs in acetonitrile at room temperature,
but effective for PN and most of its R-8 derivatives in alcohols, e.g.
2-propanol, ethanol or methanol. This is ascribed to photoreduction,
involving a spectroscopically hidden, probably (n, pi) singlet state.