Multicolor emissive carbon dot with solvatochromic behavior across the entire visible spectrum

Carbon dots (CDs) are a new class in carbonaceous family and have instigated remarkable research interests over the past decade both from fundamental and technological point of view due to its astonishing photoluminescence (PL) property, though the underlying PL mechanisms for CD are strongly disputed. Herein, we have synthesized nitrogen functionalized CDs (N-CDs) utilizing a facile and one-step hydrothermal approach. The synthesized CDs exhibit excellent solubility in a series of organic solvents and we have extensively investigated the CD-solvent interactions to understand the solvatochromic behavior of CDs which have hardly been studied. Our CDs show excitation wavelength and solvent dependent PL across nearly the entire visible spectrum without compromising the PL quantum yield (CD shows high quantum yield for both blue and red region in some selected solvents). The origin and spectral shift of PL property in different solvents are also thoroughly studied. These observations suggest that the hydrogen bonding between N-CDs and protic solvents is the primary driving force in controlling the PL in the system whereas both dipolar interaction and hydrogen bond acceptance basicity (β) of aprotic. solvents are to be counted for the irregular PL behavior of CDs. Interestingly, the CD-polymer solutions also provide better quantum yield compare to the bare CD which suggests that by monitoring the interaction between CD and polymer in different solvents we can tune the PL property of CD which can find potential applications in diverse fields.