Department of Chemistry and Pharmacy, Laboratory of Materials Science and Nanotechnology , CR-INSTM , Via Vienna 2 , 07100 Sassari , Italy.
Published: January 2020
AI Article Synopsis
Article Abstract
Understanding the luminescence of carbon dots is a highly challenging task because of the complex reactions involved in the synthesis process. Several by-products form at different reaction stages and become possible sources of emission. Citrazinic acid and its derivatives, in particular, have been identified as intermediates that give rise to blue fluorescence. Full comprehension of the optical properties of citrazinic acid itself is, however, still lacking. In particular, citrazinic acid has the property of forming different tautomers and aggregates such as dimers. However, the nature of these chemical species and the correlation with their relative optical properties have been only partially explored. In the present work, we have used a combination of spectroscopic techniques, UV-visible and fluorescence spectroscopy, time-resolved photoluminescence and computational simulation, to study the different species which citrazinic acid forms in water as a function of CZA molarity. A monomer-to-dimer transformation and a hypsochromic shift are observed with concentration. The monomer is in the keto structure and does not form other tautomers while the dimers are fluorescent J-type aggregates. The formation of aggregates strongly modulates the optical properties of citrazinic acid.
Key Laboratory of High-precision Computation and Application of Quantum Field Theory of Hebei Province, College of Physics Science and Technology, Hebei University, Baoding 071002, PR China. Electronic address:
The effect of aggregation configuration of molecular fluorophore citrazinic acid (CZA) on the photoluminescence (PL) properties of carbon dots (CDs) has been investigated using first-principles method. The structural stability of all aggregates has been analyzed, and the results show that the most stable structures are J-type CZA aggregates with head-to-tail configurations and the CZA/CD aggregates are bonded by replacing H atoms on the CD edges with de-OH from the pyridine ring of CZA. The luminescent properties of CZA/CD aggregates are mainly affected by the binding modes and binding sites.
Under isochoric and solvent-free conditions, the reaction between ammonium formate and citric acid results in a deeply purple reaction product with fluorescent properties. This brings this reaction in the realm of bio-based fluorophores and bottom-up carbon nanodots from citric acid. The reaction conditions are optimized in terms of UV-vis spectroscopic properties and, subsequently, the main reaction product is separated.
Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Physical Chemistry I, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany.
Carbon nanodots (CNDs) synthesized from citric acid and formyl derivatives, that is, formamide, urea, or N-methylformamide, stand out through their broad-range visible-light absorbance and extraordinary photostability. Despite their potential, their use has thus far been limited to imaging research. This work has now investigated the link between CNDs' photochemical properties and their chemical structure.
Herein, we report the characterization of two types of luminescent carbon dots (CDs) synthesized by the hydrothermal treatment of citric acid and -aconitic acid by using ammonia solution as a nitrogen dopant. The lateral size range of nanoparticles for CDs lies in the range of 3-15 nm. The intense blue photoluminescence (PL) was emitted by the CDs at around 409-435 nm under the excitation of 320 nm.
Carbon nanodots (CNDs) were photochemically altered to produce dihydrogen under light irradiation. Within the complex structure of CNDs, photo-oxidation takes place at citrazinic acid molecular fluorophore sites. Important is the fact that the resulting CND materials have a dual function.
