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

## TL;DR

Scientists developed a reusable glass surface that changes color when exposed to colorless liquids, allowing easy and quick detection using light absorption.

## Contribution

This is the first demonstration of a solvatochromic dye-coated glass surface for detecting and distinguishing colorless solvents.

## Key findings

- Glass surfaces modified with stilbazolium dye showed unique UV/vis absorption changes for over 20 solvents.
- The method enables real-time, nondestructive solvent detection without derivatization.
- Principal component analysis confirmed the ability to distinguish structurally similar solvents.

## Abstract

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.