A fluorescence "turn-on" sensor for detecting hydrazine in environment

•A novel recognition site, 5-chlorothiophene-2-carbonyl chloride, which was used as an electron donor combined with coumarin to form a PET fluorescence probe for detecting hydrazine.•The combination of 5-chlorothiophene-2-carbonyl chloride and coumarin endowed the probe excellent selectivity and sensitivity towards hydrazine.•The probe could operate over a wide pH region (4–10) owing to the strong bonding ability between 5-chlorothiophene-2-carbonyl chloride and coumarin. Hydrazine (N2H4) has been classified as an environmental contaminant and human carcinogen owing to its high toxicity. Being exposed to high levels of hydrazine can cause irreversible damage to human bodies. Hence, it is significant to explore an effective method to selectively recognize and detect it. In this work, a new “turn-on” fluorescence probe, coumarin-thiophene (C-T), was designed based on PET (photo-induced electron transfer) mechanism by employing 5-chlorothiophene-2-carbonyl chloride as a electron donor and coumarin as a electron acceptor. The flourescence could be recovered due to the interruption of PET by stripping the 5-chlorothiophene-2-carbonyl chloride when treated with hydrazine. The mechanism was further verified through 1H NMR titration and spectral analysis. Additionally, The probe exhibited a high selectivity towards hydrazine over other common ions and amine-containing species with a distinct fluorescence enhancement at 450 nm. The probe could operate over a wide pH region (4–10) with a detection limit as low as 0.0047 μM (1.5 ppb). Furthermore, it could selectively detect hydrazine in different water samples which indicated its potential for practical applications.