Reversible on/off switching of fluorescence via esterification of carbon dots

Abstract

We demonstrate a simple, facile, and reversible on/off fluorescence switching by functionalization of carbon dots (CDs) via esterification. The CDs synthesized from citric acid show pH-dependent photoluminescence (PL), with higher PL intensity observed at pH 7 than at pH 1. The hydroxyl and carboxyl group-bearing CDs were also esterified with different alcohols, and their PL properties were studied. It is interesting to note that in all the cases, low PL intensity of CDs at pH 1 can be transformed into a high PL system by esterification of CDs. However, at neutral pH 7, the PL intensity was found to be lower after esterification of CDs. Moreover, at pH 1, the subsequent hydrolysis of esterified CDs again results in low PL intensity, thereby demonstrating the reversibility of the process.