•Novel NIR dyes displayed excellent photo-physical properties.•A fluorescent sensor for Hg2+ ions was constructed using the dyes as a platform.•Calculations support the reaction.•Hg2+ fluorescent sensor was capable of imaging Hg2+ in living cells.A series of NIR fluorescent dyes have been synthesized and characterized. These new dyes displayed excellent photo-physical properties including large Stokes shifts, high fluorescence quantum yields, good photo-stability and low cytotoxicity. Significantly, these novel NIR dyes are superior to the traditional rhodamine dyes, displaying strong emission in the NIR region as well as the rhodamine-like ON–OFF fluorescence switching mechanism. In addition, using one of the new dyes as a platform, a novel Hg2+ fluorescent sensor was constructed which was capable of imaging Hg2+ in living cells, demonstrating the practical value of these new dyes. Finally, to understand the mechanism of action of the sensors and their enhanced fluorescence properties, we performed quantum chemical calculations with the B3LYP exchange functional employing 6-31G basis.

A new rhodamine B derivative T1 has been rationally synthesized and displayed selective Pd(II)-amplified absorbance and fluorescence emission above 540 nm in methanol–water. Upon the addition of Pd(II), the spirolactam ring was unfolded and a 1:1 metal-ligand complex formed, which can be used for “naked-eyes” detection. In addition, fluorescence imaging experiments of Pd2+ in HepG2 living cells showed its valuable application in biological systems.A new rhodamine B “off–on” Probe T1 has been rationally synthesized and displayed selective Pd(II)-amplified absorbance and fluorescence emission in methanol–water. Upon the addition of Pd(II), the spirolactam ring was unfold and a 1:1 metal-ligand was formed, which can be used for “naked-eye” detection and living cells fluorescence imaging.

A rhodamine-based probe for Fe3+ was prepared and confirmed by X-ray crystallography. The probe exhibited highly selective and sensitive recognition toward Fe3+ with distinct color change. Interestingly, the probe-Fe3+ complex could detect CN− according to the strong co-ordination ability of cyanide to Fe3+. The whole recognition mechanism was explored through Job's plot, MS data and theoretical calculations. Importantly, the probe was further used for detecting Fe3+ in living cells and mouse, which exhibited excellent fluorescence imaging.

Employing the “off-on” switching of the spirocyclic moiety in rhodamine B derivatives, two highly selective and sensitive probes for Fe3+ were prepared and confirmed by X-ray crystallography. An obvious fluorescent enhancement was observed in the presence of Fe3+, accompanied by significant color changes, which can be used for “naked-eye” detection. Moreover, confocal laser scanning microscopy experiments have proven that the probes were successfully used for fluorescence imaging in HepG2 cells.

A series of deep red fluorescent dyes were synthesized and characterized. The optical properties, theoretical calculations, and cytotoxicity of these dyes were investigated. The practical applications of the dyes were also evaluated by fluorescence imaging in living cells. Compared to Rhodamine B (RB), the emission wavelengths of compounds 3a–e were extended to the deep red region (emission maximum ranging from 620 to 650 nm) in MeOH. Furthermore, compounds 3a–e exhibited wider Stokes shifts from 100 to 150 nm. We also performed time dependent density functional theory (TDDFT) theoretical calculations of 3a–e based on the density functional theory (DFT) optimized structures of the ground S0 state and the first excited S1 state. To test the application of these dyes, we constructed a new Hg2+ fluorescent probe T-2 based on 3d and evaluated its feasibility for fluorescence imaging in living cells. The results suggest that these novel deep red fluorescent dyes can be used a platform to construct fluorescent probes for bioimaging applications.

Two novel rhodamine-active probes G2 and R2 were designed and synthesized, which adopted a 1:1 binding stoichiometry and showed highly selective sensing for Fe3+ ions over other metal ions in EtOH–H2O (1:1, v/v, Tris–HCl pH=7.4) in the fluorescence and ultraviolet spectra. Cytotoxicity and bioimaging studies by PC12 and L929 indicated that the probes were low cytotoxic, cell permeable and suitable for detecting Fe3+ in living cells.

A simple colorimetric and fluorescent chemosensor MP was designed and synthesized and its selective signaling behaviors toward Cu2+ were investigated. Under the optimized conditions, the sensor exhibited specific absorbance-on and fluorescence-on responses to Cu2+ only, which can be tuned for detection with the naked eye. These remarkable properties may allow Cu2+ to be detected directly in the presence of the other examined metal ions. The limit of detection for Cu2+ was up to 0.096 μM. As a fluorescence turn-on sensor, cell experiments showed MP can permeate through cell membranes and react to Cu2+ within living cells.

Three novel rhodamine-based probes were designed and synthesized. The probes exhibited highly selective and sensitive recognition toward Fe3+ over other metal ions via the rhodamine ring-opening approach, which can be used for “naked-eyes” detection. In addition, fluorescence imaging experiments of Fe3+ in living cells demonstrated their valuable application in biological system.

Based on Rhodamine, two novel fluorescent Hg2+ chemosensors(R1, R2) were synthesized from inexpensive starting materials. They were designed and synthesized with o-aminophenol and o-phenylenediamine derivatives as the Hg2+ chelator, the comparison between the photophysical properties of two chemosensor molecules was made. The chemosensors were designed with a photoinduced electron transfer(PET) mechanism. After binding to Hg2+ which blocks the PET process, the fluorescence intensity of the chemosensors was enhanced by up to 15-fold. They exhibit very strong fluorescence responses to Hg2+ and have remarkably higher selectivity for Hg2+ than for other metal ions including K+, Na+, Ca2+, Mg2+, Cd2+, Mn2+, Ni2+, Co2+, Zn2+, Cu2+, Cr3+, Fe3+, Pb2+, Ag+, Al3+, Fe2+ and Sn2+ in Tris-HCl/sodium phosphate buffer. The fluorescence enhancement of R2 towards Hg2+ maintains stable in wide pH span(6.4–8.8) aqueous solutions.

Eight metal–organic complexes were synthesized, characterized and evaluated as catalysts for the synthesis of phenylacetic acid. After tests on catalytic activity and catalyst recovery, two Co(II) complexes were proved to be good catalysts in the carbonylation reaction for their enhanced thermal stability and easy recovery from the reaction mixture. The novel catalysts show broad application prospects as they could be used in both homogeneous and two-phase catalytic systems. The catalytic stability of the complexes was also studied by performing consecutive batch runs with the same catalyst sample. The yield was reduced by 2 % first, then by 5 %. After the third batch, it was observed that the phenylacetic acid yield was reduced by less than 10 %, which indicated a high catalytic stability. Orthogonal tests were carried out to optimize experimental conditions. Moreover, the possible mechanism of the catalyzed carbonylation reaction was proposed. In the catalytic cycle, the cobalt complexes are first coordinated by carbon monoxide, and then are attacked by the electrophilic benzyl chloride, react with carbon monoxide afterwards, finally obtain the phenylacetic acid salt under alkaline conditions. During the catalytic cycle, the catalyzed carbonylation reaction has three transition states as carbonyl cobalt complexes, benzyl cobalt complexes and benzyl carbonyl cobalt complexes.

Six new 1-ferrocenesulfonyl-2-benzimidazole derivatives were prepared by the reaction of ferrocenesulfonyl chloride with benzimidazole derivatives in the presence of dichloromethane and n-tetrabutylammonia bromide. The yields of these six new ferrocenesulfonyl benzimidazole derivatives were about 80%. The structures characteristic were confirmed by IR, 1H-NMR, Elemental analysis and MS. The crystal structure of compound a2 was determined via X-ray single crystal diffraction and it belongs to monoclinic system with space group C2/c, and the unit cell parameters are α = 2.8252(2) nm, b = 0.97696(7) nm, c = 1.64828(12) nm, α = 90°, β = 92.053(2)°, γ = 90°, V = 4.5466(6) nm3, Z = 8, F (000) = 2024, Mr = 481.40, Dc = 1.407 g/cm3, µ = 0.784 mm−1, R1= 0.0495, wR2= 0.1517. The results show that the reactions of 2-alkylbenzimidazoles containing active hydrogen with ferrocenesulfonyl chloride gave 1- ferrocenesulfonyl-2-alkylbenzimidazoles in good yields.