Fluorophore Identification Of Several Carbon Dots As Well As Their Phenylenediamine Modifiers

Carbon dots derived from carbohydrates attracted extensive interests due to wonderful luminescence,lower preparation cost and toxicity as well as convenient preparation.However,the accurate structure information was difficult to be grasped since carbon dots were a mixture composed of various components with similar properties.It was difficult to be isolated and purified.As to the fluorescent mechanism,there were several explanations.In this work,fluorophores in the carbon dots prepared by two carbohydrates as well as the nitrogen-doped carbon dots were demonstrated with experimental results.The details were described as follow.1.A convenient approach of purifying carbon dots was reported herein.Hydrothermal treatment on glucose solution in the presence of hydrogen peroxide was carried out at 180℃ for 1 h.The obtained solution was disposed with ethyl acetate.The carbon dots(CDs)with blue emission were extracted almost completely.Thus the purified CDs were obtained after removing the solvent.The fluorescent emission was 450 nm and quantum yield was 7.18%.The fluorescence of CDs could be quenched by NaClO,KMnO4,aniline and Fehling’s solutions.Additionally,the added CDs solution could fade the color of KMnO4.The CDs mixed with Fehling’s solution produced erythrine precipitate.All the phenomena proved that the C=C bond and the aldehyde in CDs and they were vital fluorophore of CDs.Also,it was demonstrated that the quenching by Fe3+ was due to the coordination between Fe3+ and CDs.This provided a potential way of measuring hemoglobin in aqueous medium.2.Chemical modifications with m-phenylenediamine on such CDs were implemented under hydrothermal treatment at 180℃ for 2 h for preparing nitrogen-doped CDs.The results indicated that the fluorescent quantum yield of CDs was enhanced terrifically and value reached 52.69%,which was much higher than that of CDs.And the fluorescent emission shifted to 516 nm.They performed well in cellular imaging of MCF-7.These demonstrated that the modification with p-phenylenediamine favored the red shift of emission and enhancement of quantum yield.Moreover,the fluorescence could be quenched by KMnO4,NaClO,aniline and Fehling’s solutions.The nitrogen-doped CDs could fade pink KMnO4 solution and produce erythrine precipitate with Fehling’s solution.All these results demonstrated that the C=C bond and the aldehyde were still the vital fluorophores of such nitrogen-doped CDs.3.Another carbon dots were prepared with hydrothermal disposing on citric acid in the presence of hydrogen peroxide at 180℃ for 1 h(represented with c-CDs).They were mixed with o-,m-and p-phenylenediamine respectively and successive hydrothermal treatment were carried out at 180℃ for 2 h for preparing nitrogen-doped c-CDs(represented with c-NCDs-1,c-NCDs-2 and c-NCDs-3 respectively).The experimental results demonstrated that the nitrogen doping on c-CDs was completed via the amidation.The fluorescent quenching by KMnO4 and Fehling’s solution as well as the photographs of fading KMnO4 solution and the precipitate with Fehling’s solution proved that the C=C bond and the aldehyde were the fluorophores of c-CDs,c-NCDs-1,c-NCDs-2 and c-NCDs-3.Their fluorescent emissions were 435,429,499 and 591 nm respectively.These agreed with the results obtained by ab initio calculations approximately.The fluorescent quantum yields were 6.86%,67.26%,35.26%and 4.99%respectively.Such results exhibited the small blue shift caused by modification with o-phenylenediamine and the red shifts by m-and p-phenylenediamine with an obvious enhancement of quantum yield.Summarily,C=C bond and aldehyde in the carbon dots derived from glucose or citric acid as well as the modifiers(carbon dots were used as precursor)were the vital fluorophores.The modifications with phenylenediamine might provide an approach of realizing obvious red shift of the fluorescent emission and increase of the fluorescent quantum yield.