Strong Coupling of Carbon Quantum Dots in Liquid Crystals

Carbon quantum dots (CDs) have recently received a tremendous amount ofinterest owing to their attractive optical properties. However, CDs have broad absorption andemission spectra limiting their application ranges. We herein, for thefirst time, show synthesis ofwater-soluble red emissive CDs with a very narrow line width (similar to 75 meV) spectral absorbance andhence demonstrate strong coupling of CDs and plasmon polaritons in liquid crystallinemesophases. The excited state dynamics of CDs has been studied by ultrafast transient absorptionspectroscopy, and CDs display very stable and strong photoluminescence emission with aquantum yield of 35.4% and a lifetime of similar to 2 ns. More importantly, we compareJ-aggregate dyeswith CDs in terms of their absorption line width, photostability, and ability to do strong coupling,and we conclude that highlyfluorescent CDs have a bright future in the mixed light-matter statesfor emerging applications in future quantum technologies.