Polarity Adaptive Carbon Dots: Photoluminescence in Heterogeneous Environments

Abstract

Carbon dots (CDs) dissolving in heterogeneous environments such as solvents with very different polarities, ionic liquids, and emulsion gels can greatly expand the application in numerous scenarios. However, currently reported amphiphilic CDs usually aggregate at low concentrations in heterogeneous environments (especially for water), which is detrimental to the luminescence of CDs due to aggregation-caused quenching (ACQ) effect. In this work, four types of “polarity adaptive carbon dots” (pad-CDs) that can dissolve in water, organic solvents, ionic liquids, and even emulsion gels are designed. The introduction of hydrophilic imidazole ionic liquids (ILs) provided abundant functional groups on the surface of CDs derived from phenylenediamine (PDA) isomers. Thus, the pad-CDs can maintain uniform dispersion over a wide concentration range even in water. Spectral analysis for pad-CDs in seven kinds of solvents shows that the surface dipole moment of pad-CDs changed and the intramolecular charge transfer (ICT) state is generated after excitation when pad-CDs adapted to the solvent polarity. Subsequently, heterogeneous environments with microscopic bicontinuous and microscopic phase separation are set up to observe the PL of pad-CDs. All selected pad-CDs adapted to heterogeneous environments, showing bright PL and modifying the corresponding environment simultaneously.