Simultaneous and Reversible Triggering of the Phase Transfer and Luminescence Change of Amidine-Modified Carbon Dots by CO₂

The ability to reversibly manipulate the surface nature of luminescent nanoparticles upon external stimulation enables the development of advanced optical probes for biological sensing and data encoding. Herein, we report the synthesis of a new class of smart carbon dots (CDs) via surface modification of amine-enriched CDs with CO2-responsive groups of amidine. We present that alternative CO2 and N2 bubbling can not only lead to a reversible phase transfer of the CDs between an organic phase and an aqueous phase but also give rise to a corresponding reversible luminescence change between blue and cyan-green. We attribute these observations to changes in both the surface chemistry and the emission states of the CDs triggered by the alternative CO2/N2 introduction. We also find a similar luminescence change of the CDs upon alternative exposure to a humid vapor of CO2 and a mixture of NH3 and N2 at room temperature, allowing them to be used as a new class of optical materials for optical encoding.