A salicylal-derived Schiff base L was synthesized and exploited as a fluorescence probe for its selective detection of Co2+. L exhibited enhanced fluorescence response at 350 nm for Co2+ in ethanol medium, distinguishing Co2+ from other cations with high selectivity. The formation of a 4:1 complex between L and Co2+ was suggested by Job’s Plot. Additionally, the fluorescence intensity was directly proportional to the concentration of Co2+ (R2 = 0.9910) from 8.0 × 10−7 to 2.0 × 10−6 mol L−1 with a detection limit of 7.82 × 10−7 mol L−1 (3σ) under optimized conditions. The small molecular compound could be used as a promising fluorescent probe for monitoring levels of Co2+ in environmental and physiological systems.

A novel UV-visible chemosensor, 4-methyl-2-((quinolinyl-8-amino)methyl)phenol (MQAMP), was designed and synthesized. The spectral properties of its free and Cu2+-coordinated forms were characterized. Under the optimized conditions, MQAMP showed selective and sensitive sensing for copper ions in an ethanol solution. The binding of Cu2+ to MQAMP caused a marked enhancement of the absorbance, and an about 100 nm red-shift of the maximum absorption wavelength. Other ions including Mo6+, Li+, Cs+, As3+, Ca2+, Na+, Cd2+, K+, Mg2+, Pt2+, Sr2+, Ba2+, Al3+, Cr6+, Be2+, Fe3+, Ni2+, F−, CH3COO−, SO42−, NO3−, Cl−, CO32−, and SO32− displayed no significant interference in this detection of Cu2+. The chemosensor exhibited a dynamic response range for Cu2+ from 1.0 × 10−6 to 1.0 × 10−5 mol L−1 with a detection limit of 1.1 × 10−7 mol L−1 (3σ).

•A novel isonicotic acid hydrazide Schiff base was discovered as colorimetric probe for Cu (II) detection.•Addition of Cu2+ to the solution of DHIH resulted in a rapid color change from colorless to yellow.•An obvious new absorption band appeared at the range of 400–440 nm.•The chemosensor was selective and sensitive for Cu (II) determination.A novel isonicotic acid hydrazide Schiff base derivative N′-(3,5-di-tert-butyl-2-hydroxy-benzylidene) isonicotinohydrazide (DHIH) has been synthesized and developed as a high selective and sensitive colorimetric probe for Cu2+ determination. Addition of Cu2+ to the solution of DHIH resulted in a rapid color change from colorless to yellow together with an obvious new absorption band appeared at the range of 400–440 nm by forming a 1:1 complex. Experimental results indicated that the DHIH could provide absorption response to Cu2+ with a linear dynamic range from 1.0 × 10−5 to 1.0 × 10−4 mol/L. The detection limit of Cu2+ was 5.24 × 10−7 mol/L with good tolerance of other metal ions.

A metal-to-metal relay recognition was discovered with sequence specificity via a fluorescence ‘off-on-off’ phenomenon. We present here the synthesis of a new N,N-bis(2-pyridylmethyl)amine-based fluorescent sensor termed NBPA and its application as a selective relay probe for sensing of free trace zinc and copper ions. The addition of Zn2+ to NBPA causes a drastic enhancement of fluorescent intensity by the formation of a 1:1 NBPA–Zn2+ complex whereas other cations have no response. Moreover, Cu2+ can induce fluorescence quenching in the NBPA–Zn2+ system by the formation of a 1:1 NBPA–Cu2+ complex confirmed by Job's Plot. The signal change of the sensor is based on the chelation-enhanced fluorescence (CHEF) effect of NBPA–Zn2+ with the inhibition of the photoinduced electron transfer (PET) effect and the paramagnetic nature of Cu2+ to the NBPA–Zn2+ system. Under optimized conditions, the fluorescence intensity is linear to the concentration of Zn2+ and Cu2+ separately, exhibiting good linearities from 1.0 × 10−6 M to 8.0 × 10−6 M and 1.0 × 10−6 M to 1.0 × 10−5 M (R2 = 0.9996 and R2 = 0.9914) with detection limits of 7.89 × 10−7 M and 1.27 × 10−7 M, respectively. Furthermore, the rapid, selective feature enables the proposed sensor to be promising in monitoring Zn2+ and Cu2+ in biological and environmental research with good accuracy and precision.

•A novel compound FMPPA was designed and synthesized as Se (IV) chemosensor.•A fluorescent enhancement signal was observed when FMPPA combined with Se (IV).•A good sensitivity and selectivity for Se (IV) determination was achieved.A novel turn-on fluorescent chemosensor, 2-(2-Formyl-4-methyl-phenoxy)-N-phenyl-acetamide (FMPPA) was designed and synthesized, and its photophysical properties were characterized. Upon coordination with Se (IV), the chemosensor showed incredible fluorescence enhancement (turn-on), other alkali, alkaline earth, transitional metal ions, and common anions including Li+, Na+, K+, Rb+, Cs+, Be2+, Mg2+, Ca2+, Sr2+, Ba2+, Ni2+, Cu2+, Cd2+, Zn2+, Mn2+, As3+, Pt4+, V5+, Fe3+, Mo6+, Al3+, CO32-, Cl−, SCN−, AC−, NO3-, F−, SO42- had no significant interference on Se (IV) determination. The chemosensor exhibits a dynamic response range for Se (IV) from 3.32 × 10−7 to 2.63 × 10−6 M, with a detection limit of 9.38 × 10−9 M (3σ).