Rational design and synthesis of dicyanovinylene–umbelliferone as an effective water indicator for organic solvents

An umbelliferone structure has been synthesized as an efficient water probe based on the ICT effect through a D-π-A system. Rationally designed probe 5 has a hydroxyl group as an electron donor (D) and a dicyanovinylene group as an electron acceptor (A) unit representing the smaller molecular structure compared to other water sensors larger in molecular size. Absorption and emission responses of 5 in various solvents and in the presence of water have been measured. The fluorescence intensity of the probe increased with the increase in water content in organic solvents. Absorption spectra revealed the bathochromically shifted deprotonation maximum which shows a linear increment in intensity with the addition of water. Rapid color change of solutions of 5 in ACN, EtOH, and DMSO from yellowish to pinky color indicated the water presence. In addition, ICT characteristics have been confirmed through HOMO/LUMO gap calculations by the DFT method. Water content detection results (LOD = 0.00095 (wt%), 0.0020 (wt%), and 0.020 (wt%) for ACN, EtOH, and DMSO, respectively) are competitive with and even better than recent literature values. Therefore, 5 could be used as a successful water probe for detecting low levels of water content in water miscible organic solvents.