pH Dependence of Ultrafast Charge Dynamics in Graphene Oxide Dispersions

The pH dependence of emission from graphene oxide is believed to be due to the protonation of surface functional groups. In this study, we use transient absorption spectroscopy to study the sub-picosecond charge dynamics in graphene oxide over a range of pH values, observing dynamics consistent with an excited-state protonation step for pH < 9.3. The timescale of this process is ∼1.5 ps, and a corresponding change in recombination dynamics follows. A broad photo-induced absorption peak centered at 530 nm associated with excited-state protonation is also observed.