Diarylethylene guest anchored into a cyclodextrin molecular host: optical, quantum chemical studies and biological activity
The host–guest complexation between a novel guest namely; 2-(4-pyridinylbenzothiazolyl) ethane, PBE and β-cyclodextrin was studied using steady-state absorption and emission techniques. The fluorescence maximum is strongly blue-shifted with a great enhancement in the fluorescence intensity upon addition of β-CD, confirming the formation of inclusion complexes. The solid inclusion complex between PBE and β-CD has been prepared, characterised using FT-IR, X-ray diffraction and scanning electron microscope techniques. PBE is encapsulated with β-CD nanocavity and 1:1 PBE–β-CD host–guest interaction is identified. This is confirmed using semi-empirical quantum chemical calculations. PBE guest entered into the less polar cavity through the benzothiazole moiety. The negative values of enthalpy and free energy changes suggest that the encapsulation process is thermodynamically favourable. Additionally, the fluorescence is more sensitive to the micellar medium, whether it was cationic, anionic or neutral as well as metal ions like, Li+, Cu2+ and Fe3+. Finally, the antimicrobial activities of PBE guest and its inclusion complex with β-CD host are studied.