Making the Invisible Visible: Colorimetric and Spectroscopic Detection of Colorless Liquids via Solvatochromic Glass...

Absorption spectrophotometry is a reliable, efficient, and widely used analytical technique across scientific and industrial fields; however, its applicability becomes limited when the analyte lacks a visible-region chromophore and therefore appears colorless. To extend its applicability to colorless substances, glass surfaces functionalized with a solvatochromic dye were prepared and spectroscopically evaluated. This study demonstrates, for the first time, the use of glass covalently modified with a stilbazolium-based solvatochromic dye as a robust and reusable transducer for the selective detection and discrimination of colorless organic solvents. The stilbazolium-based dye, structurally derived from Brooker's merocyanine, was covalently bound to the surface of glass beads and slides via a triethoxysilyl group. The resulting materials exhibited distinct changes in their UV/vis absorption spectra, depending on the solvent, manifested as shifts in absorption band positions and variations in intensity. Unique spectral signatures for more than 20 different solvents, including structurally similar compounds, were successfully resolved, as demonstrated by principal component analysis. Compared to previous approaches using solution-phase indicators or derivatization, this method offers a nondestructive, real-time, and reusable platform for chemical sensing. These changes enabled not only the visual color discrimination of colorless solvents but also their qualitative analysis by using spectrophotometry without the need for derivatization.