Host–guest interaction between fluoro-substituted azobenzene derivative and cyclodextrins

An azobenzene derivative (F-azo-COOH) was synthesized and could be E/Z isomerized by visible light. The host–guest interaction between F-azo-COOH and cyclodextrins (CDs) in alkaline aqueous solution was studied by NMR spectroscopy for the first time. The results revealed that F-azo-COOH did not form a stable host–guest complex with α-CD. However, both trans- and cis-F-azo-COOH could form stable 1 : 1 complexes with β-CD. Most interestingly, cis-F-azo-COOH could fit the cavity of β-CD more tightly (3.0 ± 0.3 × 103 M−1) than its trans form (2.1 ± 0.2 × 103 M−1), which was completely opposite to the conventional azobenzene/β-CD system.