Graphene quantum dots(GQDs)have attracted increasing attention due to their favorable optical properties and have been widely used,e.g.,in the biomedical field.However,the properties related to the chemical structure ...Graphene quantum dots(GQDs)have attracted increasing attention due to their favorable optical properties and have been widely used,e.g.,in the biomedical field.However,the properties related to the chemical structure of GQDs,resulting in solventdependent optical properties,still remain unclear.Herein,we present the synthesis of long-wavelength emitting GQDs with a size of about 3.6 nm via a solvothermal method using oxo-functionalized graphene(oxo-G)and p-phenylenediamine as precursors and their structural and surface chemical analysis by transmission electron and atomic force microscopy(TEM;AFM)as well as Fourier-transform infrared,Raman,and X-ray photoelectron spectroscopy(FTIR;Raman;XPS).Subsequently,the influence of solvent polarity and proticity on the optical properties of the as-prepared GQDs bearing–OH,–NH_(2),–COOH and pyridine surface groups was investigated.Based on the results of the absorption and fluorescence(FL)studies,a possible luminescence mechanism is proposed.The observed solvent-induced changes in the spectral position of the FL maximum,FL quantum yield,and FL decay kinetics in protic and aprotic solvents of low and high polarity are ascribed to a combination of polarity effects,intramolecular charge transfer(ICT)processes,and hydrogen bonding.Moreover,the potential of GQDs for the optical sensing of trace amount of water was assessed.The results of our systematic spectroscopic study will promote the rational design of GQDs and shed more light on the FL mechanism of carbon-based fluorescent nanomaterials.展开更多
基金This research is supported by the Deutsche Forschungsgemeinschaft project No.392444269(DFG,German Research Foundation),the China Scholarship Council(CSC)supported by the DFG.C.N.and A.T.acknowledge DFG financial support via the research infrastructure grant INST 275/257-1 FUGG(project No.313713174)+2 种基金funding through ESF Research Groups 2019 FGR 0080“ESTI”and 2020 FGR 0051“GraphSens”as well as BMWi project ZF4817401VS9“TDraCon”Z.H.from Soochow University is acknowledged for conducting TEM measurements.U.R.G and L.S.gratefully acknowledge financial support by the European Metrology Programme for Innovation and Research(EMPIR)as part of the projects 18HLT02“AeroTox”The EMPIR initiative is co-funded by the European Union’s Horizon 2020 research and innovation programme and by the EMPIR participating states.
文摘Graphene quantum dots(GQDs)have attracted increasing attention due to their favorable optical properties and have been widely used,e.g.,in the biomedical field.However,the properties related to the chemical structure of GQDs,resulting in solventdependent optical properties,still remain unclear.Herein,we present the synthesis of long-wavelength emitting GQDs with a size of about 3.6 nm via a solvothermal method using oxo-functionalized graphene(oxo-G)and p-phenylenediamine as precursors and their structural and surface chemical analysis by transmission electron and atomic force microscopy(TEM;AFM)as well as Fourier-transform infrared,Raman,and X-ray photoelectron spectroscopy(FTIR;Raman;XPS).Subsequently,the influence of solvent polarity and proticity on the optical properties of the as-prepared GQDs bearing–OH,–NH_(2),–COOH and pyridine surface groups was investigated.Based on the results of the absorption and fluorescence(FL)studies,a possible luminescence mechanism is proposed.The observed solvent-induced changes in the spectral position of the FL maximum,FL quantum yield,and FL decay kinetics in protic and aprotic solvents of low and high polarity are ascribed to a combination of polarity effects,intramolecular charge transfer(ICT)processes,and hydrogen bonding.Moreover,the potential of GQDs for the optical sensing of trace amount of water was assessed.The results of our systematic spectroscopic study will promote the rational design of GQDs and shed more light on the FL mechanism of carbon-based fluorescent nanomaterials.
