Carbon nanostructures are promising electrode materials for energy storage devices because of their unique physical and chemical properties. Modification of the surface improves the electrochemical properties of those materials because of the changes in morphology, diffusion properties, and inclusion of additional contributions to redox processes. Oxygen-containing functional groups and nitrogen doped into the carbon matrix significantly contribute to the electrochemical behavior of reduced graphite oxide (RGO). In this work, RGO was synthesized during hydrothermal treatment of graphite oxide with a hydrazine sulfate aqueous solution. Different amounts of hydrazine sulfate were used to synthesize RGO with different nitrogen contents in the structure, and the same synthesis conditions made it possible to obtain a material with a similar composition of oxygen-containing functional groups. The materials with different nitrogen concentrations and similar amounts of oxygen were compared as electrode materials for a supercapacitor and as a negative electrode material for a Li-ion battery. It was shown that the presence of oxygen-containing functional groups has the greatest influence on the behavior and efficiency of supercapacitor electrode materials, while nitrogen atoms embedded in the graphene lattice play the largest role in lithium intercalation.

Optoacoustic imaging, also known as photoacoustic imaging, promises micron-resolution noninvasive imaging in biology at much deeper penetration (>cm) depths than e.g. fluorescence. However, the loud, photostable, NIR-absorbing molecular contrast agents which would be needed for optoacoustic imaging of enzyme activity remain unknown: most organic molecular contrast agents are simply repurposed fluorophores, with severe shortcomings of photoinstability or phototoxicity under optoacoustic imaging conditions, which are consequences of their slow S1→S0 electronic relaxation rates. We now disclose that known fluorophores can be rationally modified to reach ultrafast S1→S0 rates, without much extra molecular complexity, simply by merging them with molecular switches. Here, we merge azobenzene switches to cyanine dyes to give ultrafast relaxation (<10 ps, >100-fold faster). Even without adapting instrument settings, these azohemicyanine optoacoustic imaging agents deliver outstanding improvements in signal longevity (>1000-fold increase of photostability) and signal loudness (here: >3-fold even at time zero). We show why this still-unexplored design strategy can offer even stronger performance in the future, as a simple method that will also increase the spatial resolution and the quantitative linearity of photoacoustic response even over extended longitudinal imaging. By bringing the world of molecular switches and rotors to bear on unsolved problems that have faced optoacoustic agents, this practical strategy may be a crucial step towards unleashing the full potential, in fundamental studies and in translational uses, of optoacoustic imaging.