A simple coumarin based sensor 1 has been synthesized from the condensation reaction of 7-hydroxycoumarin and ethylenediamine via the intermediate 7-hydroxy-8-aldehyde-coumarin. As a multiple analysis sensor, 1 can monitor Zn2+ with the fluorescence enhanced at 457 nm, and ratiometric detection at 290 nm, 350 nm and 420 nm in DMF/H2O (1/4, v/v) medium. Sensor 1 can also monitor Mg2+ with the fluorescence enhanced at 430 nm, and ratiometric detection at 290 nm, 370 nm and 430 nm in DMF medium through the interaction of chelation enhance fluorescence (CHEF) with metal ions. Furthermore, 1 also can monitor F− with the fluorescence enhanced at 460 nm, and ratiometric detection at 290 nm and 390 nm in DMF medium simultaneously via hydrogen bonding and deprotonation with F− anion. Spectral titration, isothermal titration calorimetry and mass spectrometry revealed that the sensor formed a 1:1 complex with Mg2+, Zn2+ or F-, with stability constants of 4.5 × 106, 3.4 × 106, 8.0 × 104 M−1 respectively. The complexation of the ions by 1 was an exothermic reaction driven by entropy processes. Furthermore, the sensor exhibits good membrane-permeability and was capable of monitoring at the intracellular Zn2+ level in living cells.

•A coumarin-quinoline probe based on Al3+ induced fluorescence resonance energy transfer (FRET) response has been studied.•The probe exhibited ratiometric fluorescence recognition for Al3+ ions.•The probe is suitable for fluorescent imaging of Al3+ in living cells.•The probe detects Al3+ with a very low detection limit in neutral aqueous medium.•Test paper studies provided an easy way to detect Al3+, which suggests this system is a good candidate for Al3+-sensing.A coumarin-quinoline based fluorescence resonance energy transfer (FRET) system (TCQ) has been synthesized and employed as a ratiometric fluorescence probe. The selective fluorescent response of the probe TCQ toward Al3+ was devised by employing a quinoline moiety as a FRET energy donor with a coumarin moiety as an energy acceptor. The quinoline emission at 390 nm decreased and the coumarin emission at 480 nm increased concurrently on addition of Al3+ under excitation wavelength at 253 nm. The TCQ probe exhibited high selectivity for Al3+ as compared to other tested metal ions and the ratiometric sensing of Al3+ was determined by plotting the fluorescence intensity ratio at 480 nm and 390 nm versus Al3+ ion concentration. Moreover, test strips based on TCQ were fabricated, which were found to act as a convenient and efficient Al3+ ion detection kit. Furthermore, this system has been used for imaging of Al3+ in living cells.

N,N′-bis(4-methoxysalicylide)benzene-1,4-diamine (S1) was synthesized from 4-methoxysalicylaldehyde and p-phenylenediamine and it was found to exhibit interesting aggregation-induced emission enhancement (AIEE) characteristics. In aprotic solvent, S1 displayed very weak fluorescence, whilst strong emission was observed when in protic solvent. The morphology characteristics and luminescent properties of S1 were determined from the fluorescence and UV absorption spectra, SEM, fluorescence microscope and grading analysis. Analysis of the single crystal diffraction data infers that the intramolecular hydrogen bonding constitutes to a coplanar structure and orderly packing in aggregated state, which in turn hinders intramolecular C-N single bond rotation. Given that the three benzene rings formed a large plane conjugated structure, the fluorescence emission was significantly enhanced. The absolute fluorescence quantum yield and fluorescence lifetime also showed that radiation transition was effectively enhanced in the aggregated state. Moreover, the AIEE behavior of S1 suggests there is a potential application in the fluorescence sensing of some volatile organic solvents.

Similar to the larger members of the cucurbituril family, such as cucurbit[8]uril (Q[8]), the smallest member, cucurbit[5]uril (Q[5]), can also induce room-temperature phosphorescence (RTP) of α-naphthol (1) and β-naphthol (2). The relationship between the RTP intensity of 1 and 2 and the concentration of Q[5] or Q[8] suggests that the mechanism underlying the Q[5] complex-induced RTP is different from that of the Q[8]-induced RTP for these luminophores. The crystal structures of 1–Q[5]–KI, 2–Q[5]–KI, 1–Q[5]–TlNO3, and 2–Q[5]–TlNO3 systems show that in each case Q[5] and the respective metal ions, K+ or Tl+, form infinite ⋯Q[5]–M+–Q[5]–M+⋯ chains that surround the luminophores. Although these tube- or wall-like structures are likely destroyed in solution, the key interaction between the convex-shaped outer walls of Q[5] and the plane of the aromatic naphthols, via π⋯π stacking and C–H⋯π interactions, is postulated to be essentially maintained leading to a microenvironment that holds the luminophore and the heavy atom perturber together; such a model is supported by the observed Q[5] complex-induced RTP of the above naphthols. With respect to this, a high Q[5]/luminophore concentration was employed in an endeavour to promote the formation of π⋯π stacking and C–H⋯π interactions similar to those observed in the crystal structures of the 1– or 2–Q[5]–K+ and –Tl+ systems. In keeping with the proposed model, the RTP of each system is quenched when Q[5] is replaced by the alkyl-substituted Q[5] derivatives, decamethylQ[5] and pentacyclohexanoQ[5]. This is in agreement with the substituent groups on the surface of the metal-bond Q[5] obstructing the naphthol molecule from accessing the convex glycouril backbone of Q[5].

The synthesis and spectroscopic studies of a thiacalix[4]arene-based sensor of 1,3-alternate-25,27-bis(2-aminoethoxy)-26,28-bis(2-methoxyethyl)-thiacalix[4]arene linked 4-chloro-7-nitrobenzofurazan (NBD-Cl) are described. The properties of the compound were evaluated and show that it is a colorimetric and fluorescence sensor for Ag+ and AcO−. The addition of Ag+ results in a red shift of the absorption spectrum of the sensor, which is clearly visible to the naked eye, accompanied by a strong quenching of the fluorescence. With the addition of AcO−, the fluorescence was severely quenched, and the absorbance increased significantly, with a new absorption band appearing at shorter wavelength. This demonstrated that the multifunctional sensing compound prepared from a novel thiacalix[4]arene was highly selective for AcO−.

A new rhodamine B schiff-base fluorescent sensor (1) was synthesized by a one-step condensation reaction of rhodamine B ethylenediamine and acetylacetone. The structure of 1 was characterized by single crystal X-ray crystallography, 1H NMR, MS and IR spectroscopy. Studying its fluorogenic and colorimetric behaviors towards various metal ions, high sensitivity and selectivity were achieved for Fe3+ over other commonly coexistent metal ions, which were accompanied by ring opening of a rhodamine spirocycle framework. In the ethanol aqueous medium (v/v = 4/6, Tris–HCl buffer, pH = 7.0), the presence of Fe3+ induces the formation of a 1-ion complex, which was deduced by spectroscopy, HPLC and electrochemical methods. The limit of detection for Fe3+ determinations was low to 0.11 μM (fluorescence measurement) and 1.6 μM (UV–vis measurement), respectively, indicating the potential application of 1 for the determination of trace Fe3+ ions in neutral medium.

A new tripodal rhodamine B derivative 2 was designed and synthesized by tripodal trialdehyde and rhodamine B hydrazide for the first time. This derivative could be used as a fluorescent chemosensor for the selective and sensitive determination of copper(II) in Tris-HCl buffer and ethanol aqueous mixed media. Under the optimum conditions described herein, fluorescence enhancement at 557/577 nm was linearly related to the concentration of copper(II) in the range of 0.10 to 10.00×10−5 mol·L−1, with a correlation coefficient of R2=0.9964 (n=15) and a detection limit of 1.129×10−7 mol·L−1 (the relative standard deviation for five repeated measurements at 4.00×10−5 mol·L−1 Cu(II) was 2.2%). The absorbance measurements at 557 nm were linearly related to the concentration of Cu(II) in the range of 0.50 to 25.00×10−5 mol·L−1, with a correlation coefficient of R2=0.9948 (n=13) and a detection limit of 3.338×10−7mol·L−1.

Similar to the larger members of the cucurbituril family, such as cucurbit[8]uril (Q[8]), the smallest member, cucurbit[5]uril (Q[5]), can also induce room-temperature phosphorescence (RTP) of α-naphthol (1) and β-naphthol (2). The relationship between the RTP intensity of 1 and 2 and the concentration of Q[5] or Q[8] suggests that the mechanism underlying the Q[5] complex-induced RTP is different from that of the Q[8]-induced RTP for these luminophores. The crystal structures of 1–Q[5]–KI, 2–Q[5]–KI, 1–Q[5]–TlNO3, and 2–Q[5]–TlNO3 systems show that in each case Q[5] and the respective metal ions, K+ or Tl+, form infinite ⋯Q[5]–M+–Q[5]–M+⋯ chains that surround the luminophores. Although these tube- or wall-like structures are likely destroyed in solution, the key interaction between the convex-shaped outer walls of Q[5] and the plane of the aromatic naphthols, via π⋯π stacking and C–H⋯π interactions, is postulated to be essentially maintained leading to a microenvironment that holds the luminophore and the heavy atom perturber together; such a model is supported by the observed Q[5] complex-induced RTP of the above naphthols. With respect to this, a high Q[5]/luminophore concentration was employed in an endeavour to promote the formation of π⋯π stacking and C–H⋯π interactions similar to those observed in the crystal structures of the 1– or 2–Q[5]–K+ and –Tl+ systems. In keeping with the proposed model, the RTP of each system is quenched when Q[5] is replaced by the alkyl-substituted Q[5] derivatives, decamethylQ[5] and pentacyclohexanoQ[5]. This is in agreement with the substituent groups on the surface of the metal-bond Q[5] obstructing the naphthol molecule from accessing the convex glycouril backbone of Q[5].