A Fluorescent Temperature Probe Based on the Association between the Excited States of 4-(N,N-Dimethylamino)benzonitrile and β-Cyclodextrin

A temperature probe based on the fluorescence properties of the two excited states of 4-(N,N-dimethylamino)benzonitrile (DMABN) in equilibrium with β-cyclodextrin (CD) in aqueous solution is presented. The fluorescence intensity of the Franck−Condon excited state (FB) as a function of temperature shows a straight line with a correlation better than 0.99 in the 283−308 K temperature interval. On the other hand, the fluorescence intensity of the twisted internal charge-transfer state (FA) remains constant in the same temperature interval because the binding of DMABN in the A* state to CD is isoenthalpic and entropy driven. It is found that the FA/FB ratio is independent of the excitation intensity at a specified temperature, shows a linear relationship with temperature, and allows temperature measurements with a resolution of ±2.5 K.