The properties of carbon-based nanomaterials can be altered and engineered through the deliberate introduction of certain structural "imperfections" or defects. The challenge, however, is to control the number and type of these defects. In the case of carbon nanotubes—microscopically small tubular compounds that emit light in the near-infrared—chemists and materials scientists at Heidelberg University led by Prof. Dr. Jana Zaumseil have now demonstrated a new reaction pathway to enable such defect control. It results in specific optically active defects—so-called sp3 defects—which are more luminescent and can emit single photons, that is, particles of light. The efficient emission of near-infrared light is important for applications in telecommunication and biological imaging.