Solvent Effect On Metal Ion Recognition Of An Optical Chemosensor Based On Rhodamine B Modified By Coumarin

Optical chemosensor based on fluorometric and colorimetric methods has been widely used for the qualitative and quantitative detection of various ions and biomolecules which are closely related to the life activities. It has been a rapid-developed analytical method with distinct advantages in the past two decades. In this work, we successfully synthesized an optical chemosensor L which utlizing two classical fluorescent materials, rhodamine and coumarin, to serve as a chromophore or receptor, and the functional group of the Schiff base as a linker. The work focused on the solvent effect of L during the metal ion recognition process. The main content is illustrated as follows:1. Investigate the metal ion sensing behavior of L in DMSO/H2O mixed system. L detected Cu2+ ion with high selectivity, sensitivity and a fast response time by changing its color from colorless to magenta in DMSO/H2O=1:1 solution. The limit of detection for Cu2+ was calculated to be as low as 28 nM. The possible binding mode of L with Cu2+ ion was studied using the Job’s plot, HRMS, FTIR spectroscopy and 1H NMR spectroscopy titration. Importantly, test strips containing L were fabricated as a naked-eye indicator for Cu2+ ion in pure water samples.2. Investigate the metal ion sensing behavior of L in ethanol and THF system. L could recognize Ca2+, Cd2+ or Al3+ simultaneously in ethanol via PET or FRET mechanism and could fluorometric and colorimetric dual-sensing of Al3+ for detaching Ca2+ or Cd2+ from the L-Ca2+ and L-Cd2+ complex. While the detection of the sensor could be switched for Zn2+ with high sensitivity and a fast response time by regulating solvents from ethanol to THF. The possible binding mode of L with Ca2+, Cd2+, Al3+ and Zn2+ ion was studied preliminary using the Job’s plot, FTIR spectroscopy or HRMS.3. Investigate the metal ion sensing behavior of L in other solvent systems (acetone, acetonitrile, DMF). L could recognize different metal ions from different fluorescence signal outputs in acetone, acetonitrile or DMF via PET or FRET mechanism. The sensing behavior was relatively complicated when compared with other solvent systems.