Formation of vesicles between negatively charged carbon quantum dots and cationic surfactant cetylpyridinium chloride (CPC) due to oxidative photo induced electron transfer

Abstract

The tuning of photo physical properties of highly emissive carbon quantum dots which was synthesized from citric acid in DMF medium through solvothermal method is investigated inside micelles formed by different types of surfactants like cationic surfactant cetylpyridinium chloride (CPC), cetrimonium bromide (CTAB), anionic surfactant sodium dodecyl sulfate (SDS) and neutral surfactant polyethylene glycol tert-octyl phenyl ether (TX100), polyoxoethylene lauryl ether (BRIJ-35). Interestingly, only CPC interacts with greater extent and formed co-assembly with negatively-charged carbon quantum dots (CQDs) whereas other surfactants like CTAB, SDS, TX100 and BRIJ-35 do not alter the fluorescence intensity extensively. This results in the formation of a non fluorescent vesicle. No phase separation was observed over the large concentration barrier of the CPC surfactant. However, no such vesicle formation takes place for another cationic surfactant CTAB excluding the role of only electrostatic interaction. The synthesized vesicle is characterized by various techniques including HRTEM, DLS. For the aqueous solution of CQDs having concentration of 0.5 mg/ml, addition of CPC leads to formation of different sized vesicles of size 40 nm to 100 nm. The driving force behind this formation of non-fluorescent vesicles is oxidative photo induced electron transfer which is revealed by the highest occupied molecular orbital (HOMO) –lowest unoccupied molecular orbital (LUMO) interaction between the donor (CQDs) and the acceptor (CPC). We trust such type vesicle can be a suitable alternative for drug carriers, biomarkers and other various applications also.