N-(di)icosyl-substituted benzo[a]phenoxazinium chlorides: Synthesis and evaluation as near-infrared membrane probes Sarala Naik, Carla M. A. Alves, Paulo J. G. Coutinho, M. Sameiro T. Gonçalves European Journal of Organic Chemistry, 2011 Five benzo[a]phenoxazinium chlorides containing alkyl chains with twenty carbon atoms at the 5‐ or 9‐positions of the tetracyclic ring were efficiently synthesised and characterised by UV/Vis and NIR spectroscopy. The absorption and emission maxima in ethanol occur in the range 627–641 nm and 645–676 nm, respectively, with quantum yields varying from 0.14 to 0.38. Preliminary photophysical studies with these fluorochromophores in zwitterionic [2,3‐bis(palmitoyloxy)propyl‐2‐(trimethylammonio)ethyl phosphate, DPPC] and cationic (N,N‐dimethyl‐N‐octadecyloctadecan‐1‐aminium bromide, DODAB) vesicles were carried out. The results showed that the new benzo[a]phenoxazinium derivatives are able to detect the gel to liquid‐crystalline lipid phase transition through variations in either the extent of H‐aggregation or in the acid–base equilibrium.
