First stable (Z)-configuration of cyanostilbene derivative: An effective “turn-on“ fluorescent sensor for lysine in aqueous media

Abstract

Due to the rapid E/Z isomerization of cyanostilbene under light or heating, the stable (Z)-configuration of cyanostilbene was hard to be obtained although many (E)-cyanostilbene derivatives had been reported as excellent fluorescence sensor. In this work, the first stable (Z)-configuration of cyanostilbene derivative (Z)-CS bridged by crown-ether chain was designed and synthesized under the irradiation of UV365 and heating. The stable (Z)-configuration was attributed to the short bridging crown-ether chain which restricted the E/Z isomerization of cyanostilbene. (Z)-CS exhibited the weak AIE effect in H2O/DMSO system, but showed the strong “turn-on” fluorescence enhancement after adding lysine. The detection limit of (Z)-CS for lysine attained 1.34 × 10−7 M. The selective sensing behavior for lysine was stable in pH = 6–9 and was little interfered by other species. The 1:1 sensing mechanism was proposed by the investigation of Job’s plot, 1H NMR and MS binding spectra. The sensing ability of (Z)-CS was successfully applied for analyzing lysine in urine samples of human body. (Z)-CS also displayed the good bioimaging performance with enhanced blue-purple fluorescence after detecting lysine. The work not only presented an effective fluorescence sensor for lysine in aqueous media, but also confirmed firstly the excellent application prospect of stable (Z)-configuration of cyanostilbene as fluorescence probe in complicated and living environment.