Synthesis and applications of amino-functionalized carbon nanomaterials

Carbon-based nanomaterials (CNMs) have attracted considerable attention in the scientific community both from a scientific and an industrial point of view. Fullerenes, carbon nanotubes (CNTs), graphene and carbon dots (CDs) are the most popular forms and continue to be widely studied. However, the general poor solubility of many of these materials in most common solvents and their strong tendency to aggregate remains a major obstacle in practical applications. To solve these problems, organic chemistry offers formidable help, through the exploitation of tailored approaches, especially when aiming at the integration of nanostructures in biological systems. According to our experience with carbon-based nanostructures, the introduction of amino groups is one of the best trade-offs for the preparation of functionalized nanomaterials. Indeed, amino groups are well-known for enhancing the dispersion, solubilization, and processability of materials, in particular of CNMs. Amino groups are characterized by basicity, nucleophilicity, and formation of hydrogen or halogen bonding. All these features unlock new strategies for the interaction between nanomaterials and other molecules. This integration can occur either through covalent bonds (e.g., via amide coupling) or in a supramolecular fashion. In the present Feature Article, the attention will be focused through selected examples of our approach to the synthetic pathways necessary for the introduction of amino groups in CNMs and the subsequent preparation of highly engineered ad hoc nanostructures for practical applications.

Synthesis and characterization of a porphyrin-crown ether conjugate as a potential intermediate for drug delivery application

The development of synthetic strategies for functional building units plays a central role in supramolecular chemistry. Both porphyrin and crown ethers have attracted the attention of researchers worldwide owing to their unique properties. It is envisioned that the integration of the two molecules will result in hybrid materials with potential applications in many fields. In the present study, a new porphyrin derivative 3 appended with four 18-crown-6 (18C6) ether moieties was synthesized through the Suzuki-Miyaura coupling of boronic ester porphyrin 1 and 4-bromobenzo-18-crown-6 2 in 80% yield. Porphyrin 3 was fully characterized by 1H/[Formula: see text]C NMR spectroscopy and high resolution mass spectrometry. The tendency of the 18C6 to form host-guest complexes with ammonium cations was exploited to assemble cation responsive hybrid material of porphyrin 3 and ammonium immobilized mesoporous silica nanoparticles (MSNs). Furthermore, the potential application of the 3/MSNs conjugate as a cation-responsive drug delivery vehicle was investigated in solution by UV-vis and fluorescence spectroscopies.

Light-Controlled Regioselective Synthesis of Fullerene Bis-Adducts

Multi-functionalization and isomer-purity of fullerenes are crucial tasks for the development of their chemistry in various fields. In both current main approaches-tether-directed covalent functionalization and supramolecular masks-the control of regioselectivity requires multi-step synthetic procedures to prepare the desired tether or mask. Herein, we describe light-responsive tethers, containing an azobenzene photoswitch and two malonate groups, in the double cyclopropanation of [60]fullerene. The formation of the bis-adducts and their spectroscopic and photochemical properties, as well as the effect of azobenzene photoswitching on the regiochemistry of the bis-addition, have been studied. The behavior of the tethers depends on the geometry of the connection between the photoactive core and the malonate moieties. One tether lead to a strikingly different adduct distribution for the E and Z isomers, indicating that the covalent bis-functionalization of C₆₀ can be controlled by light.

Design, Synthesis, and Functionalization Strategies of Tailored Carbon Nanodots

Over the past decades, considerable efforts have been devoted to synthesizing nanostructured materials with specific properties that ultimately shape their function. In the carbon nanotechnology era, for nanomaterials such as fullerenes, carbon nanotubes, and graphene, the main focus has been on the organic functionalization of these nanostructures, in order to tailor their processability and applicability. Carbon-based dots, quasi-spherical nanoparticles with a shape under 10 nm, have popped up into this context especially due to their versatile synthesis and intriguing properties, mainly their fluorescence emission. Even though they were discovered through the top-down route of cutting large carbon nanostructures, in recent years the ease and flexibility of the bottom-up synthesis have allowed this carbon-based class of nanomaterials to advance at a striking pace. However, the fast speed of research and publication rate have caused a few issues that affect their classification, purity criteria, and fluorescence mechanisms. As these are being progressively addressed, the true potential and applicability of this nanomaterial has started to unravel. In this Ariticle, we describe our efforts toward 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 multicomponent synthetic approach, using arginine and ethylenediamine as starting materials. By controlling the reaction conditions, in just 3 min, 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 postfunctionalization 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.

An all-liquid crystal based high-performance laser protection system via linear/nonlinear dual-mechanisms

An all-liquid crystal based laser protection system based on mesogenic [60]fullerences and CLCs is reported that integrates an excellent optical limiting response, a broadband protection range, and good practicability simultaneously.

Tailoring Colors by O Annulation of Polycyclic Aromatic Hydrocarbons

The synthesis of O-doped polyaromatic hydro- carbons in which two polycyclic aromatic hydrocarbon sub units are bridged through one or two O atoms has been achieved. This includes high-yield ring-closure key steps that, depending on the reaction conditions, result in the formation of furanyl or pyranopyranyl linkages through intramolecular C-O bond formation. Comprehensive photophysical measurements in solution showed that these compounds have exceptionally high emission yields and tunable absorption properties throughout the UV/Vis spectral region. Electrochemical investigations showed that in all cases O annulation increases the electron-donor capabilities by raising the HOMO energy level, whereas the LUMO energy level is less affected. Moreover, third-order nonlinear optical (NLO) measurements on solutions or thin films containing the dyes showed very good values of the second hyperpolarizability. Importantly, poly(methyl methacrylate) films containing the pyranopyranyl derivatives exhibited weak linear absorption and NLO absorption compared to the nonlinearity and NLO refraction, respectively, and thus revealed them to be exceptional organic materials for photonic devices.

Conjugated Porphyrin Dimers: Cooperative Effects and Electronic Communication in Supramolecular Ensembles with C60

Two new conjugated porphyrin-based systems (dimers 3 and 4) endowed with suitable crown ethers have been synthesized as receptors for a fullerene-ammonium salt derivative (1). Association constants in solution have been determined by UV–vis titration experiments in CH₂Cl₂ at room temperature. The designed hosts are able to associate up to two fullerene-based guest molecules and present association constants as high as ∼5 × 10⁸ M^–1. Calculation of the allosteric cooperative factor α for supramolecular complexes [3·1₂] and [4·1₂] showed a negative cooperative effect in both cases. The interactions accounting for the formation of the associates are based, first, on the complementary ammonium-crown ether interaction and, second, on the π–π interactions between the porphyrin rings and the C₆₀ moieties. Theoretical calculations have evidenced a significant decrease of the electron density in the porphyrin dimers 3 and 4 upon complexation of the first C₆₀ molecule, in good agreement with the negative cooperativity found in these systems. This negative effect is partially compensated by the stabilizing C₆₀–C₆₀ interactions that take place in the more stable syn-disposition of [4·1₂].