Chemical sensing failed by aggregation-caused quenching? A case study enables liquid/solid two-phase determination of N2H4

Hydrazine (N2H4), a highly toxic substance and pollutant, can lead to serious environmental contamination and is harmful to human health. Currently, most developed N2H4 sensors rely on quartz cuvette experiments. But such solution samples are not portable and are difficult to collect. The implementation of sensing materials in functional hosts is very challenging since the majority of organic fluorophores possess the notorious effect of aggregation-caused quenching in solid state. Here, a dual-state emission (DSE) molecule 5-(9-phenyl-9H-carbazol-3-yl)thiophene-2-carbaldehyde (LG) with single-crystal structure has been achieved. In particular, LG is highly emissive both in the solid state and solution phase. LG exhibits satisfactory selective response to N2H4 compared to various interferential analytes and superior sensitivity with a detection limit as low as 76.2 nM. The response mechanism has been verified as a reaction-based spontaneous formation of hydrazone Schiff base derivative, as supported by fluorescence and UV–vis spectra, 1H NMR, High-resolution mass spectrometry (HRMS) and density functional theory (DFT) calculation. Notably, chemical sensing by thin layer chromatography (TLC) solid plate was used to signal the gaseous phase N2H4 recognition event. A deeper understanding of the physiological functions necessary to track N2H4 in MCF-7 cells has been realized. These new findings will elucidate unique perspectives on the rational design of responsive probes capable of controlling optical profiles under various environments.