Biindenylidene-3,10,30-trione: An Interesting Solvatochromic Molecule and Its Applications for Visual pH Detection and DCM Identification

The development of highly sensitive and visual analytical methods for monitoring pH change has always attracted great attention due to significant roles in various fields including food, environmental and biological systems. In this paper, a dual-response sensor for pH detection, [1,2']biindenylidene-3,1',3'-trione L, was synthesized from substrate indane-1,3-dione, and its structure was confirmed by ¹H NMR, ¹³C NMR, ESI–MS and single crystals. Interestingly, sensor L exhibits solvatochromic properties and visualized color changes at different poplar solutions, and it can show significant changes in fluorescence intensity, UV–Vis absorbance and color at moderate acidic (pH = 3.52–5.03) and strong basic conditions (pH = 13.09–13.27) based on intramolecular proton transfer (IPT) mechanism. These results indicate that L can act as a double functional probe for the analysis and visual detection of pH change under moderate acidic and strong basic conditions in a quite narrow pH range. In addition, L can also selectively identify solvent CH₂Cl₂ by inducing larger blue-shift in wavelength and increase in fluorescence intensity, which means that it may be used as an indicator for monitoring trace amount of CH₂Cl₂. The potent applicantions for sensor L were also investigated and that it could conveniently be made into a series of strips for pH detection was indicated.