Absorption and Fluorescence Properties of Oxidized and N-doped Graphene Quantum Dots:A Time-dependent DFT Study

Absorption and emission properties of oxidized graphene quantum dots(GQDs) and amino functionalized GQDs(NG) were explored by B3 LYP method combined with 6-31G(d) basis set.The oxygen- and nitrogen-containing groups can tune the intensity as well as the wavelength of absorption and emission.The groups such as hydroxyl,carboxyl,amino,amide,and pyridine-like N can appropriately lengthen the absorption and emission wavelength of GQDs.However,the carbonyl group,graphitic-like N,and pyrrolic-like N obviously decrease the oscillator strength and lengthen the emission wavelength of GQDs out of the visible region.The lowest excited state Sof NG has the strongest emission in investigated complexes,which indicates that it is an excellent luminous material.The theoretical investigations verify that the oxygen- and nitrogen-related groups can tune the luminescence of GQDs.The fluorescence quenching of GQDs reduced by ammonia mainly depends on the graphitic-like and pyrrolic-like N.