On the Molecular Origin of Photoluminescence of Nonblinking Carbon Dot

The molecular origin of the photoluminescence (PL) of carbon dots (CDs) is not fully understood. In this article it is shown that CDs are composed of aggregated 2-pyridone derivatives employing π–π stacking and H-bonding, etc. The PL quantum yield of this CD is quite high in aqueous medium (∼75%). Unlike literature reports the PL emission maximum of this CD is excitation wavelength independent, and PL decay follows a single-exponential decay equation. These CDs have a long PL lifetime (from ∼10 to 15 ns), so that solvation is complete before emission. The extent of trap states could be reduced quite significantly. A high PLQY and long and single-exponential PL lifetime and it’s polarity dependence would make this CD a suitable probe for FRET and FLIM. It could be shown that unlike literature reports this CD as a single particle does not blink. Unlike literature reports where CDs are bleached within a few seconds these CDs at the single-particle level are alive for about a few minutes. All these aggregation-induced much improved optical properties will make this CD a suitable optical emitter at the ensemble as well as single-particle level toward bioimaging. As the molecular origin is now known several optical properties can now be tuned.