Aggregation-induced dual-emission carbon dots for visual discrimination of methanol from ethanol

Discriminating methanol from ethanol is critically important for preventing fatal poisoning incidents and ensuring industrial quality control, yet it remains a significant challenge due to their nearly identical physicochemical properties. Conventional analytical techniques are time-consuming, expensive, and require sophisticated instrumentation. Fluorescent probes offer a promising alternative, but most reported sensors rely on single-emission quenching mechanisms that are susceptible to interference. Therefore, developing a simple, low-cost, yet highly selective strategy for visual discrimination of methanol from ethanol is urgently needed.

We developed carbon dots (m-CDs) from m-phenylenediamine and n-butyraldehyde that exhibit aggregation-induced dual-emission: strong blue fluorescence at 440 nm in ethanol and distinct green emission at 490 nm in methanol. This solvatofluorochromism enables rapid, visual, and quantitative methanol detection across two linear ranges (10-60 and 60-100 vol%) with a LOD of 0.57 vol%, accompanied by a naked-eye blue-to-green color transition under UV light. The sensor shows excellent selectivity over common alcohols and satisfactory recoveries (96.3-102.5%) in real industrial samples, validated by gas chromatography. Mechanistic studies integrating spectroscopy, microscopy, and computational simulations reveal that methanol promotes tight stacking (∼3.5 Å) via a dual hydrogen-bonding network, facilitating intermolecular charge-transfer and red-shifted emission, whereas ethanol maintains a dispersed state (>5.1 Å) with localized blue emission.

This work establishes a complete multiscale structure-property relationship, from solvent polarity to aggregation structure to electronic coupling, providing a low-cost screening tool for detecting gross methanol adulteration in industrial solvents and fundamental insights into aggregation-induced emission mechanisms in carbon nanomaterials. These findings guide the design of next-generation responsive optical probes for practical and fundamental applications.