Photoluminescent carbon nanomaterials, or carbon dots (CDs), are an emerging class of materials that has recently attracted considerable attention for biomedical and energy applications. They are defined by characteristic sizes of <10 nm, a carbon-based core, and the possibility to add various functional groups at their surface for targeted applications. These nanomaterials possess many interesting physicochemical and optical properties, including tuneable light emission, dispersibility and low toxicity. In this Review, we categorize how chemical tools impact the properties of CDs. We look for pre-and post-synthetic approaches for the preparation of CDs and their derivatives or composites. We then showcase examples to correlate structure, composition, and function and use them to discuss the future development for this class of nanomaterials. monomer/polymer as starting materials. Historically, the top-down strategy was first exploited and consisted mainly of electrochemical or chemical oxidation of graphite. 7 While these approaches can yield relatively large quantities of CDs, they usually employ harsh conditions (in terms of voltage applied or chemical oxidant used), long synthetic times, and still need post-synthetic procedures to tune the optoelectronic properties. From the fluorescence perspective, oxidative cutting of carbon sources leads to more structural defects, resulting in less appealing photoluminescence properties.Currently, the bottom-up syntheses are more popular and will be the focus of this Review. In addition to the multitude of molecular precursors available, other benefits include multiple choices of thermal treatments, quicker reaction times, and more uniform properties in the final material. The choice of precursors and synthetic procedures (i.e. pre-synthetic control) affects the physicochemical properties of CDs in terms of size, graphitization degree, surface functional groups, and doping. Nevertheless, the structural features of the precursors can be retained in the nanoparticles, allowing for some degree of predictability. Single-component, to a certain extent, and multi-component reactions enable the use of straightforward doping strategies. These include heteroatoms (examples here include boron, nitrogen, sulfur, selenium, or a combination of them) and metals (such as lanthanides).Besides pre-synthetic control, engineering the surface composition via post-synthetic approaches is a promising way to optimize and expand the utilization of CDs (Fig. 1b). Post-synthetic strategies usually affect the surface functional groups of the CDs since they are generally inefficient in changing properties and chemical composition of the core. Exploiting their surface chemistry also prompted the development of multifunctional CD-based materials (Fig. 1c).There are many excellent sources of information about the intricacies of CDs properties [7][8][9][10][11] and their applications, [12][13][14][15][16] as well as their progress in comparison to traditional inorganic quantum dots. 17 At first, emphas...

A facile bottom-up approach to carbon nanodots (CNDs) is reported, using a microwave-assisted procedure under controlled conditions. The as-prepared nitrogen-doped CNDs (NCNDs) show narrow size-distribution, abundant surface traps and functional groups, resulting in tunable fluorescent emission and excellent solubility in water. Moreover, we present a general method for the separation of NCNDs by low-pressure size-exclusion chromatography, leading to an even narrower size distribution, different surface composition, and optical properties. They display among the smallest size and the highest FLQYs reported so far. (13)C-enriched starting materials produced N(13) CNDs suitable for thorough NMR studies, which gave useful information on their molecular structure. Moreover, they can be easily functionalized and can be used as water-soluble carriers. This work provides an avenue to size- and surface-controllable and structurally defined NCNDs for applications in areas such as optoelectronics, biomedicine, and bioimaging.

In this Account, we describe our efforts towards the synthesis, purification, characterization and applications of carbon nanodots. Special attention was dedicated to designing and customizing the optoelectronic properties of these nanomaterials, as well as their applications in hybrid and composite systems. Our approach is centered on a bottom-up, microwave-assisted hydrothermal synthesis. We have successfully exploited a multi-component synthetic approach, using arginine and ethylenediamine as starting materials. By controlling the reaction conditions, in just three minutes, blue-emitting carbon nanodots become accessible. We have improved this approach by designing and tuning the emissive, electrochemical and chiroptical properties of these nanoforms. On the other hand, we have used post-functionalization reactions as a tool for conjugation with suitable partners and for further tuning the surface chemistry. The combination of these two approaches has produced a number of carbon nanodots that can be investigated in fields ranging from biology to materials chemistry and in applications spanning from nanomedicine to energy conversion.

The chirality of (nano)structures is paramount in many phenomena, including biological processes, self-assembly, enantioselective reactions, and light or electron spin polarization. In the quest for new chiral materials, metallo-organic hybrids have been attractive candidates for exploiting the aforementioned scientific fields. Here, we show that chiral carbon nanoparticles, called carbon nanodots, can be readily prepared using hydrothermal microwave-assisted synthesis and easily purified. These particles, with a mean particle size around 3 nm, are highly soluble in water and display mirror-image profile both in the UV–Vis and in the infrared regions, as detected by electronic and vibrational circular dichroism, respectively. Finally, the nanoparticles are used as templates for the formation of chiral supramolecular porphyrin assemblies, showing that it is possible to use and transfer the chiral information. This simple (and effective) methodology opens up exciting opportunities for developing a variety of chiral composite materials and applications.