Characterization of room temperature phosphorescence of propranolol and the chiral discrimination between R- and S-isomers

Upon addition of a small amount of bromocyclohexane, propranolol displays room temperature phosphorescence in γ-cyclodextrin solution without deoxygenation. Several factors including the pH, and the concentration of γ-cyclodextrin and bromocyclohexane, which affect the room temperature phosphorescence (RTP) intensity and room temperature phosphorescence lifetime of propranolol are studied in detail. Under optimal conditions, the room temperature phosphorescence lifetimes of propranolol enantiomers are measured. The experimental results show that the associated phosphorescence decay curves can be best fitted to mono-exponential patterns and room temperature phosphorescence lifetimes of R- and S-propranolol are 4.60 ms and 5.74 ms, respectively. The difference of the room temperature phosphorescence lifetimes of R- and S-propranolol is 22.05%. Based on that, chiral discrimination of propranolol enantiomers is carried out successfully by time-resolved phosphorescence.