Interaction of graphene with excited and ground state rhodamine revealed by steady state and time resolved fluorescence

The fluorescence decay of rhodamine 6G (R6G) became biexponential when chemically derived few-layer graphene (CDG) is present, indicating the occurrence of new emitting species. To reveal the nature of the species, the binding behavior between CDG and R6G was studied by time-resolved, steady state fluorescence, UV–vis absorption methods and AFM. The addition of CDG caused the dramatic change in UV–vis absorption spectrum of R6G. The evolution of isosbestic point revealed that R6G could bind to CDG in different modes. CDG titration also led to the significant quenching of the fluorescence intensity and shortening of the emission lifetime of R6G, but the data does not follow the traditional Stern–Volmer plot. Detailed analysis on absorption and fluorescence data revealed that R6G could bind to CDG and CDG aggregates in different ways to form following complexes: R6Gn–CDG, R6Gn–(CDG)2 and CDG–R6Gn–CDG, respectively. Different from other dye–graphene complex, R6G–graphene complexes are emissive, but three ground state complexes exhibit different fluorescence spectral properties and fluorescence lifetimes. The mechanism that causes R6Gn–CDG to emit differently is also discussed. R6Gn–CDG etc. complexes act as intra-molecular electron donor–acceptor pairs which undergo photoinduced electron transfer (PET) and energy transfer from R6G to CDG upon light excitation. The total rate constant of quenching due to PET and energy transfer is computed and dependent on the binding mode.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Graphene presence made the fluorescence decay of rhodamine (R6G) biexponential. ► R6G caused the self-assembly of graphene in three different modes. ► Three ground state complexes exhibit different fluorescence properties. ► Strong static and dynamic quenching of R6G fluorescence occurred by graphene. ► Fluorescence quenching due to PET does not follow the traditional Stern–Volmer plot.