Transient Depolarization Spectroscopic Study on Electronic Structure and Fluorescence Origin of Graphene Oxide

It is well-established that the electronic states of graphene oxide (GO) consist of sp² clusters with different sizes and the surrounding sp³ matrix according to recent reports. However, addressing the excitation energy migration/redistribution among those electronic states in GO-based complex systems from spectroscopic experiments is still a challenge. Here, we combine the time-resolved absorption and fluorescence depolarization experiments to reveal the excitation energy migration processes in electronic states in GO. We demonstrate that, in sp³ domains of GO, there are charge-transfer states between sp³-hybridized carbon atoms and the oxygen-containing functional groups, and the energy redistribution and charge migration in sp³ matrix occur on the time scale from subpicoseconds to tens of picoseconds. In contrast, the electronic states of sp² clusters in GO are rather localized and dominantly contribute to the excitation-wavelength-dependent red fluorescence of GO.