Ligand engineering with heterocyclic aromatic thiol doped carbon quantum dots

Abstract

Insights on the origin of photoluminescence (PL) in carbon quantum dots (CQDs) are useful to explore its application in the technological and biomedical fields. Herein, we demonstrate the use of three heterocyclic aromatic thiol ligands (namely, 2-mercaptobenzimidazole (MBI), 2-mercaptobenzothiazole (MBT) and 2-mercaptobenzoxazole (MBO)) doped CQDs (CQDs-MBI, CQDs-MBT and CQDs-MBO) to address the significance of heteroatoms in the optical and electrochemical characteristics of CQDs. Interestingly, we found that nitrogen moieties played a vital role in tailoring the optical and electrochemical properties of CQDs-MBI, CQDs-MBT and CQDs-MBO. Owing to the enriched nitrogen moieties and less surface trap states in CQDs-MBI, which exhibits superior quantum yield (QY) and lifetime than CQDs-MBT and CQDs-MBO. Moreover, for the CQDs-MBI and CQDs-MBT we achieved two sets of emission whereas for the CQDs-MBO attained three sets, also all these CQDs display both excitation independent and dependent emission behavior due to the distinct surface states which is peculiar to existing literature reports. To substantiate the importance of ligand engineering with these three different CQDs, we further investigated the electrochemical characteristics as well. These tunable optical and electrochemical properties of the three different CQDs suggest great scope in the development of new luminescent and sensor materials.