•Ethyl-2-(2-aminothiazol-4-yl)-2-(hydroxyimino)acetate was first introduced into a fluorescent probe and was served as a receptor for Fe3+ ions.•Probe L recognized specifically towards Fe3+ and exhibited fluorescence intensity enhancement in the presence of Fe3+.•The limit of detection of L for Fe3+ was 9 × 10−8 M superior to a number of reported sensors.•The 1:1 stoichiometry ratio was supported by ESI-MS of [M + Fe3+ + 2Cl−].A novel fluorescent chemosensor L based on benzimidazo[2,1-α]benz[de] isoquinoline-7-one-12-carboxylic acid as fluorophore with ethyl-2-(2-aminothiazol-4-yl)-2-(hydroxyimino)acetate as receptor was developed. L in CH3CN/H2O (v/v = 9:1, 5 mM tris, pH = 7.4) exhibited selectively fluorescence “off-on” pattern for Fe3+. Moreover, the detection limit of L for Fe3+ was 9.0 × 10−8 M. In addition, ESI-MS confirmed 1:1 stoichiometry ratio of L with Fe3+. DFT theory calculations was used to prove the hypothetical PET mechanism.

A new chemosensor, N′-[(2-hydroxyphenyl)methylidene]imidazo[1,2-a]quinoline-2-carbohydrazide (L2), was developed, which could detect Al3+ in DMSO/H2O HEPES buffer and Zn2+ in EtOH/H2O HEPES buffer. The chemosensor exhibits high selectivity and sensitivity for sensing Al3+ and Zn2+ with a fluorescence “turn-on” mode.

Fluorescent sensors N-[2-(dimethylamino)ethyl]benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxylamide (L1) and its corresponding quaternary ammonium salt L2 were prepared. Probe L1 exhibited fluorescence ‘turn-on’ response toward H+ in acetonitrile/H2O (9:1) solution based on photoinduced electron transfer (PET) process. The fluorescence intensity of L1 gradually increased about 45-fold from pH 9.2 to 4.2 with a pKa value of 6.67. L2 exhibited colorimetric response toward OH− in water. The solution color of L2 changed from yellow to colorless under visible light and changed from yellow to blue under UV light from pH 8.9 to 11.5. 1H NMR spectroscopy studies confirmed hydration of the carbonyl group (CO) in fluorophore of L2 occurred under basic condition. The reason of fluorescence enhancement of L1 toward H+ and color changes of L2 toward OH− were demonstrated by density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations with 6-31G(d) basis sets using a suite of Gaussian 03 programs.

Fluorescent sensors of N-(4-methylpiperazin-1-yl)benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxylamide (C1) and its corresponding quaternary ammonium salt (C2) were prepared. C1 showed 45-fold fluorescence turn-on response towards Cu2+ with a detection limit of 5.7 × 10−8 mol L−1 in acetonitrile–H2O (9:1) buffer solution and C2 showed 18-fold fluorescence enhancement towards Cu2+ with a detection limit of 3.4 × 10−7 mol L−1 in the same condition. The Cu2+ sensing of C1 and C2 were both based on the photoinduced electron transfer (PET) process. Such behaviors confirmed that the benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxylic acid based C1 and C2 could be utilized as fluorescent sensors for Cu2+. The mechanism of fluorescence enhancement of C1 towards Cu2+ was verified by DFT/TDDFT calculation using Gaussian 03. In addition, an obvious color change was observed when an aqueous solution of C2 was treated with aqueous NaOH. Such behavior confirms that C2 could be used as a fluorescent OH− sensor in water.

Two novel water-soluble conjugated polymers poly{3-[1-(2-trimethylammoniumacetyl)piperidine-4-methylene]thiophene-2,5-diyl chloride} (PTAPT-Cl) and poly{3-[1-(2-trimethylammoniumbutyryl)piperidine-4-methylene] thiophene-2,5-diyl chloride} (PTBPT-Cl) have been synthesized via chemical oxidative polymerization and applied as a colorimetric and fluorometric probe for the detection of metal ions. Moreover, the fluorescence detection of metal ions using previously synthesized poly[N,N,N-trimethyl-4-(thiophen-3-ylmethylene)cyclohexanaminium chloride] (PTCA-Cl) and poly[3-(1,1′-dimethyl-4-piperidinemethylene)thiophene-2,5-diyl chloride] (PDPMT-Cl) was also investigated and discussed. All four conjugated polymers exhibited high sensitivity and selectivity to Hg2+ with a fluorescence “turn-off” mode at pH 3 in aqueous solutions. The best detection limit was as low as 10−9 M without interference from other common metal ions. Consequently, the distinctive quenching of the emission bands in the presence of various metal ions can lead to qualitative and quantitative Hg2+ detection in aqueous solution by a new approach using cationic polythiophene derivatives.