From Small Molecules to Zero-Dimensional Carbon Nanodots: Chasing the Stepwise Transformations During Carbonization

Abstract

Unlike the traditional fluorescent material, carbon dots (CDs) have unique photoluminescent properties, which directly depend on several synthesis parameters during the bottom-up carbonization process. Overall photoluminescence properties of CDs are mainly regulated by the three major emissive domains of CDs, that is, (a) small molecular fluorophores, (b) graphitic aromatic domains, and (c) amorphous domains and/or surface states. However, the extent of carbonization is extremely crucial as it directs the relative populations of the three emissive domains and their interplay, which eventually regulates the overall photo-physics of carbon-based nanomaterials. Therefore, it is highly desirable to explore the molecular-level stepwise transformations of small precursor molecules to zero-dimensional CDs and eventually their critical optimization in emitting, catalytic, and optoelectronic devices. Herein, we have investigated the stepwise growth process of zero-dimensional N-functionalized CDs from small molecular precursors–citric acid and ammonia. In-depth molecular insight into the evolution of chromophore centers has been gained through detailed structure–property correlation. Structural and elemental features have been illustrated by employing proton nuclear magnetic resonance, Fourier-transform infrared, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. Furthermore, the intrinsic molecular-level transformation of CDs is nicely correlated with the evolution of the intriguing photophysical properties by detailed steady-state and time-resolved spectroscopy. In addition, the extent of aromaticity and the internal rigidity during the growth process have also been illustrated by temperature-dependent fluorescence spectroscopy. Overall, the current fundamental study will be extremely crucial for the development of CDs and their molecular-level optimization for on-demand applications.

Role of Noncovalent Interactions in N,P-Functionalized Luminescent Carbon Dots for Ultrasensitive Detection of Moisture in D2O: Boosting Visible-NIR Light Sensitivity

“…Since the discovery of carbon dots (CDs) as a new class of carbon-based fluorescent nanoparticles, they have always been in limelight due to their compelling optoelectronic properties. , The true origin of the unique photoluminescence (PL) properties of CDs was repeatedly contested over the years; so far, however, only a few mechanisms have been well accepted. The intriguing PL properties of CDs mainly come from the π-conjugated sp 2 -hybridized polycyclic aromatic domain, surface/defect states, and either free or bonded molecular fluorophores that appear during the course of carbonization. − The ease of tuning the optical properties of CDs accompanied by the trouble-free green cost-effective synthesis procedure makes CDs a potential candidate for diverse crucial applications in photonics, biophotonics, and sensing devices. , In this context, it is noteworthy that the optical properties of CDs are found to be very much sensitive to factors like the synthesis procedure, temperature, solvent variation, additive, and surface functionalities . Additionally, CDs possess remarkable water solubility, rapid sensitivity, low cytotoxicity, variable fluorescence properties, and commendable photo-stability.…”

A Theoretical Investigation into the Oligomer Structure of Carbon Dots Formed from Small-Molecule Precursors

“…In view of the possible reaction of carboxyl groups with hydroxyl and amino groups during the preparation of CDs [ 16 , 17 , 24 , 25 , 26 ], the dimerization process of two CA molecules and the formation process of dimers through an amidation reaction between CA and EDA were studied, respectively.…”

Multicolor Afterglow from Carbon Dots: Preparation and Mechanism

“…At present, CDs are considered to have a core‐shell model structure consisting of graphitized carbon cores and various functional groups surfaces. [ 172 ] As discussed before, in the bottom‐up‐based carbonization process, temperature and time directly affect the carbonization degree of CDs, resulting in the change of emission wavelength. For example, Xia et al.…”