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.