Photoluminescent Quenching of Carbon Nanodots in the Presence of Tetracyanoethylene: Quenching Sphere of Action of Carbon Nanodots

The interaction of photoluminescent carbon nanodots (CDs) with their environment underpins a fundamental factor in the design of photoluminescent CDs for various potential applications. The effect of synthesis reaction temperature on photophysical features and quenching behavior using one of the strongest electron acceptors, tetracyanoethylene (TCNE), was systematically investigated. Thorough characterization confirmed progressive carbonization and formation of sp²-hybridized carbon cores with temperature, alongside a reduction in surface oxygenated groups. Optical absorption and emission spectrum revealed the transition from surface-dominated to core-dominated emission mechanisms with temperature. Upon quenching analysis with TCNE, all CDs exhibited PL quenching and a characteristic absorption band formation at 420 nm, corresponding to the new CD-TCNE adduct formation. The quenching shows the positive deviation from the Stern-Volmer equation with a large quenching extent that follows the order CD-180 > CD-200 > CD-150. The mechanism was found to be induced by a combination of static and dynamic mechanisms, affected by the interplay within edge-functionalized groups and π-conjugated aromatic domains and their intrinsic adduct formation with TCNE. The static quenching components related to the CD-TCNE adduct formation were estimated using the quenching sphere of action model with the values of sphere volumes, <i>V</i>, and the sphere diameters in the order of CD-180 (4.1 nm) > CD-200 (3.8 nm) > CD-150 (3.5 nm). These results demonstrate that the reaction temperature critically modulates the size, electronic structure, and quenching dynamics of CDs with TCNE, facilitating control upon excited-state behavior for optoelectronic and sensing applications.