Enantioselective phosphorescence behavior of naproxen in β-cyclodextrin supramolecular complex

In the presence of small amount of 1-iodo butane (IBu) (0.1 % (v/v)), Naproxen (Nap) displays strong room temperature phosphorescence (RTP) in β-cyclodextrin (β-CD) solution without deoxygenation because of the formation of ternary complex of β-CD, Nap, and IBu. The results indicate that β-CD shows good enantiodiscrimination for (R)-Nap and (S)-Nap. The RTP intensity of (R)-Nap is larger than that of (S)-Nap, the difference being 29.2 %. Both (R)-Nap and (S)-Nap exhibit single exponential phosphorescence decay with different lifetimes of 2.535 ± 0.056 and 1.798 ± 0.076 ms for (R)-Nap and for (S)-Nap, respectively. The corresponding association constants evaluated for (R)-Nap/β-CD/IBu and (S)-Nap/β-CD/IBu ternary complexes are (8.02 ± 0.15) × 103 and (2.50 ± 0.06) × 103 L mol−1, respectively. Thus, the observation of RTP differences between (R)-Nap and (S)-Nap can be attributed to their different ability to form complexes with chiral β-CD.