Fluorescent Probes with Variable Intramolecular Charge Transfer: Constructing Closed-Circle Plots for Distinguishing DO from HO.

It is difficult to distinguish between HO and DO due to their very similar properties. Triphenylimidazole derivatives with carboxyl groups () show intramolecular charge transfer that responds to polarities and pH of solvents. Here, a series of with very high photoluminescence quantum yields (73-98%) were synthesized to distinguish DO from HO by the method of wavelength-changeable fluorescence. In a mixed THF/water solution, the increase of HO and DO contents will separately induce different pendulum-type fluorescence variations and form plots of closed circles with the same starting and ending points from which a THF/water ratio that displays the most different emission wavelengths (up to 53 nm with an LOD of 0.064 vol %) can be determined to further distinguish DO from HO. This is proved to be originated from the various Lewis acidities between HO and DO. The results of theoretical calculations and experiments suggest that, for different substituent groups in , an appropriate electron-donating effect is beneficial to distinguish between HO and DO, while the electron-pulling effect is adverse. Moreover, because the potential hydrogen/deuterium exchange does not affect the as-responsive fluorescence, this method is reliable. And this work provides a new strategy for the design of fluorescent probes for DO.