Theoretical calculations unlock secrets of carbon dots

A theoretical study by computational chemists from Palacký University’s Czech Advanced Technology and Research Institute (CATRIN) provides new insights into understanding the mechanism behind the photoluminescence of carbon dots. This article was published by The Journal of Physical Chemistry C, which also selected a graphic by Martin Pykal (CATRIN) for the supplementary cover.

Not even twenty years have passed since the discovery of a carbon dot, and yet this ‘teenager’ currently ranks among the most intensively studied nanomaterials. Numerous properties such as high stability, biocompatibility, low toxicity or intense photoluminescence make carbon dots suitable for a variety of applications ranging from medicine to optoelectronics. From the perspective of their structures, carbon dots aren’t easy to tackle. Computer simulations are another technique that also helps to map the properties of carbon dots. A research team headed by Michal Otyepka from CATRIN is one of the leading theoretical groups pushing the boundaries of scientific knowledge in this field.

Scientists followed last year’s work published in The Journal of Physical Chemistry Letters. Herein, they focused on the molecular photoemission centres (fluorophores) that can form when carbon dots are synthesized. Using computer simulations, they showed that molecular fluorophores could not only noncovalently bind to the surface of a quantum dot, but also incorporate into its structure. Then they continued to perform simulations in which they studied photoluminescence changes depending on the different positions of the molecular fluorophore.

“Our calculations showed that the environment around the molecular fluorophore and the nature of its incorporation within the carbon dot significantly influence the intensity of the emission and the colour shift of the excitation and emission. Subsequently, an excitation-emission map showed that molecular fluorophores are the main source of excitation-independent emissions with a broad emission peak,” said the main author of the publication Michal Langer.

These findings coincide with generally accepted conclusions on molecular fluorophore emission generated from experimental data. “The consistency of theoretical and experimental excitation-emission maps confirms the validity of the computational protocol used. This opens the door to studying even more complex phenomena, such as communication between different photoluminescent centres and generally excitation-dependent luminescence, which is difficult to explain solely on the basis of experiments,” added another author Miroslav Medveď.

Olomouc scientists have been devoted to this area for a long time, working intensively with a number of other researchers both domestic and from abroad. This is evidenced by various scientific papers published in collaboration with Andrey Rogach from Hong Kong or Hans Lischka from Texas, including a recent study on the mechanism for quenching carbon dot luminescence, which can be used for alcohol detection [ACS Nano 2021, 15, 6582–6593].