Ion-recognizing Cyclometalated Ruthenium Complex:Synthesis And Their Properties

Cyclometalated ruthenium complexes have much more rich photophsical and photochemical properties in comparison with those traditional ruthenium complexes involving Ru（bpy）₃²⁺（bpy=2,2’-bipyriding）due to the formation of Ru-Cσ-bond.The presence of anionic carbon can make HOMO energy levels of cyclometalated ruthenium complexes increase,which results in red-shifts of their absorption spectra.It is well known that their metal-to-ligand-charge-transfer（MLCT）absorption bands are centered above 500 nm,which make it much easier to visually and colorimetrically recognize some small molecules or ions by structural modifications.Therefore,cyclometalated ruthenium complexes have potential application in optical chemo-sensors.However,up to now,there are few reports on the ion recognition by using cyclometalated ruthenium complexes as colorimetric sensors.Herein,three new cyclometalated ruthenium complexes have been designed and synthesized successfully.The interactions between these complexes and some common ions in aqueous system were investigated,and complexes that exhibited better recognitions to some ions were obtained.The main contents are summarized as follow:1.A new cyclometalated ruthenium complex[Ru（bpy）₂（fpth）]PF₆（1,Hfpth=2-（5-formyl-2-thienyl）pyridine）was designed and synthesized.Due to the presence of thiophene group,it can interact with Hg²⁺and Cu²⁺in acetonitrile solution,which caused obvious changes in the absorption spectra of 1.The colors of the solutions changed from deep red to yellow for Hg²⁺and light red for Cu²⁺,respectively.These obvious changes indicated that 1 can serve as a colorimetric indicator for Hg²⁺or Cu²⁺.However,it is regrettable that the presence of other ions has evident interference.Moreover 1 can not do function with Hg²⁺and Cu²⁺in aqueous systems.2.A new water-soluble cyclometalated ruthenium complex was successfully synthesized and characterized Ru（bpy）₂（ptbs）⁺（2,Hptbs=3,3-dimethyl-2-（5-pyridylthiophen-2-yl）vinylbenzo[e]indolium-1-propylsulfonate）.Not only did it show excellent light absorption band centered at 506 nm with molar extinction coefficient as4.4×10⁴ M^-1cm^-1,but also showed good absorption in the near-infrared region.It can be seen that the complex displayed maximum absorption band centered at 730 nm(ε=6.3×10³ M^-1 cm^-1)with its absorption band edge extending to 1000 nm.It should be noted that 2 displayed highly sensitivity and selectivity to Hg²⁺.When Hg²⁺was added to the aqueous solution of 2,the solution color varied quickly from dark red to light yellow.Meanwhile,the detection limit of 2 to Hg²⁺was calculated to be 0.021μM,which is comparable to some excellent fluorescence sensors that reported before.3.As expected,2 demonstrated a high selectivity and sensitivity to sulfites and bisulfite,because 1,4-addition reaction occured between the complex and sulfites which resulted in obvious spectral changes.When either HSO₃^-or SO₃^2-ions wre added to the buffer（pH7.0）solution of 2,almost similar solution color and absorption changes were abserved.However,it is noticeable that the additions of HSO₃^-and SO₃^2-ions resulted in quite different absorption and solution color changes.It should be attributed to that bisulfite in pure water could liberate a small quantity of H⁺,which may induce the inter-conversion of cyclometallated thienyl ring Ru-C to the S–coordinated ring Ru-S.The different solution color changes in pure water displayed that 2 can be used as an optical chemo-sensor to distinguish HSO₃^-from SO₃^2-by naked eyes.The detection limts of 2 to HSO₃^-and SO₃^2-wrer calculated to be 0.48 and 0.43μM,respectively.4.A new cyclometalated complex[Ru（bpy）₂（ptbh）]⁺（3,Hptbh=3,3-dimethyl-2-（5-pyridylthiophen-2-yl）vinylbenzo[e]indolium-1-hexanoic acid）was successfully designed and synthesized to colorimetrically recognise Hg²⁺and SO₃^2-in aqueous system.The detection limits for 3 to Hg²⁺and SO₃^2-are 0.052μM and 1.2μM,respectively.Interestingly,when SO₃^2-was added to the HEPES buffer solution of the complex 3,the solution color varied from dark-red to light red.However,the subsequent addition of Cu²⁺to the above solutioncan resulted in the solution color recovering partly to red.As results,3 can be used a colorimetric chemo-sensor to achieve continuous recognition of SO₃^2-and Cu²⁺.