Carbon nanodots and molecular machines as bottom-up approaches to nanotechnology

The field of nanotechnology, a broad discipline committed to the design, control and manipulation of matter at the nanoscale, has advanced tremendously in the last decades. The final goal of nanotechnology is the development of novel materials, possessing at least one dimension between 1-100 nm. The controlled manipulation of materials at the nanoscale allows conveying new features, which can be dramatically different from those of their corresponding bulk counterparts. Two strategies can be adopted for the fabrication of nanomaterials. Top-down approach consists in the miniaturization of larger materials into nanomaterials; while bottom-up method relies on controlled reactions of atoms and molecular precursors to assemble complex nanomaterials. Interest in the latter strategy is growing due to the possibility to fabricate tailored nanomaterials with fine-tuned properties from molecularly engineered “building blocks”. The fil rouge of this thesis is the use of a rational bottom-up approach to build novel structures at the nanoscale, using two different strategies: a traditional bottom-up approach to obtain materials with nanometric dimensions, and a supramolecular-based approach to build molecular systems performing tasks at the nanoscale. Chapter 1 provides, initially, a general overview of nanotechnology and of respective top-down and bottom-up strategy. An emphasis on the bottom-up methods will be given. After, the synthetic bottom-up approaches for the synthesis of carbon nanomaterials, and in particular carbon nanodots, will be described, and some notable examples will be discussed. Lastly, a complementary approach to the fabrication of nanomaterials will be described, based on supramolecular chemistry. A considerable attention will be given to the synthesis and functioning of one of the most common family of systems used in this domain: artificial molecular machines. Through some specific examples, their operation will also be discussed. Chapter 2 presents the synthesis, purification, and characterization of a family of atropoisomeric carbon nanodots, via bottom-up microwave-assisted method. Contrary to other hydrophilic carbon nanodots, these nanoparticles display solubility in organic solvents. Depending on the chirality of the enantiomer employed, these chiral particles show specular profile in the UV-Visible region, as detected by electronic circular dichroism. Remarkably, one class of these carbon nanodots shows circularly polarized luminescence. Contrary to the literature precedents on carbon nanodots, this advanced optical property is observed in solution, without needing any chiral external matrix. As evidenced by morphological and chiroptical experiments, the axial chirality is transferred from molecular to the nanoscale. In this way, this property is directly encoded within nanomaterial structure, without the need for post-functionalization steps. Chapter 3 presents the synthesis and characterization of a symmetric and an asymmetric molecular axle. Both bear a recognition site for a macrocycle, allowing the formation of pseudorotaxane. Its terminal part can be dynamically stoppered, gaining control on the pseudorotaxane formation. The threading/dethreading operation in response to acid-base inputs was studied, confirming machine operation according to a ratchet mechanism, leading to the energetically-demanding trapping of the macrocycle in a high-energy state. The peculiar choice of molecular stopper allowed controlling the dethreading kinetics, ranging from obtaining kinetically-trapped out-of-equilibrium state to rapid equilibration. The solvent in which the operation occurs is fundamental in controlling the dethreading kinetics. Tuning this parameter, the machine can experience either a rapid equilibration or an observable dissipative relaxation, revealing the directional exploration of a square reaction network underlying machine operation, which can be repeated multiple times in situ.The field of nanotechnology, a broad discipline committed to the design, control and manipulation of matter at the nanoscale, has advanced tremendously in the last decades. The final goal of nanotechnology is the development of novel materials, possessing at least one dimension between 1-100 nm. The controlled manipulation of materials at the nanoscale allows conveying new features, which can be dramatically different from those of their corresponding bulk counterparts. Two strategies can be adopted for the fabrication of nanomaterials. Top-down approach consists in the miniaturization of larger materials into nanomaterials; while bottom-up method relies on controlled reactions of atoms and molecular precursors to assemble complex nanomaterials. Interest in the latter strategy is growing due to the possibility to fabricate tailored nanomaterials with fine-tuned properties from molecularly engineered “building blocks”. The fil rouge of this thesis is the use of a rational bottom-up approach to build novel structures at the nanoscale, using two different strategies: a traditional bottom-up approach to obtain materials with nanometric dimensions, and a supramolecular-based approach to build molecular systems performing tasks at the nanoscale. Chapter 1 provides, initially, a general overview of nanotechnology and of respective top-down and bottom-up strategy. An emphasis on the bottom-up methods will be given. After, the synthetic bottom-up approaches for the synthesis of carbon nanomaterials, and in particular carbon nanodots, will be described, and some notable examples will be discussed. Lastly, a complementary approach to the fabrication of nanomaterials will be described, based on supramolecular chemistry. A considerable attention will be given to the synthesis and functioning of one of the most common family of systems used in this domain: artificial molecular machines. Through some specific examples, their operation will also be discussed. Chapter 2 presents the synthesis, purification, and characterization of a family of atropoisomeric carbon nanodots, via bottom-up microwave-assisted method. Contrary to other hydrophilic carbon nanodots, these nanoparticles display solubility in organic solvents. Depending on the chirality of the enantiomer employed, these chiral particles show specular profile in the UV-Visible region, as detected by electronic circular dichroism. Remarkably, one class of these carbon nanodots shows circularly polarized luminescence. Contrary to the literature precedents on carbon nanodots, this advanced optical property is observed in solution, without needing any chiral external matrix. As evidenced by morphological and chiroptical experiments, the axial chirality is transferred from molecular to the nanoscale. In this way, this property is directly encoded within nanomaterial structure, without the need for post-functionalization steps. Chapter 3 presents the synthesis and characterization of a symmetric and an asymmetric molecular axle. Both bear a recognition site for a macrocycle, allowing the formation of pseudorotaxane. Its terminal part can be dynamically stoppered, gaining control on the pseudorotaxane formation. The threading/dethreading operation in response to acid-base inputs was studied, confirming machine operation according to a ratchet mechanism, leading to the energetically-demanding trapping of the macrocycle in a high-energy state. The peculiar choice of molecular stopper allowed controlling the dethreading kinetics, ranging from obtaining kinetically-trapped out-of-equilibrium state to rapid equilibration. The solvent in which the operation occurs is fundamental in controlling the dethreading kinetics. Tuning this parameter, the machine can experience either a rapid equilibration or an observable dissipative relaxation, revealing the directional exploration of a square reaction network underlying machine operation, which can be repeated multiple times in situ

Control on dissipative kinetics reveals the entropically-dominated essence of interlocked molecular machines

The operation of nanomachines is fundamentally different from that of their macroscopic counterparts. In particular, the role of solvent is critical, yet rarely associated with machine functionality. Here we study a minimal model of one of the most advanced molecular machines, to gain control on its operation by engineering components and the employed solvent. Operation kinetics was modulated over more than four orders of magnitude, and could be fine-tuned. Leveraging solvent properties, it was possible to realize multiple cycles of the molecular machine operation while monitoring it. Our work expands the capabilities of acid-base powered molecular machines, contributing to the development of systems that leverage solvent properties to expand their functionality

Transfer of Axial Chirality to the Nanoscale Endows Carbon Nanodots with Circularly Polarized Luminescence

We report the synthesis, purification and characterization of chiral carbon nanodots starting from atropoisomeric precursors. The obtained atropoisomeric carbon nanodots are soluble in organic solvents and have good thermal stability, which are desirable features for technological applications. The synthetic protocol is robust, as it supports a number of variations in terms of molecular doping agents. Remarkably, the combination of axially chiral precursors and 1,4-benzoquinone as doping agent results in green-emissive carbon dots displaying circularly polarized luminescence. Dissymmetry factors of |3.5|x10(-4) are obtained in solution, without the need of any additional element of chirality. Introducing axial chirality expands the strategies available to tailor the properties of carbon nanodots, paving the way for carbon nanoparticles that combine good processability in organic solvents with engineered advanced chiroptical properties

Photochemical bromination of 2,5-dimethylbenzoic acid as key step of an improved alkyne-functionalized blue box synthesis

Cyclobis(paraquat-p-phenylene) is a highly electron-deficient macrocycle, widely used as a molecular receptor for small electron-rich molecules. Inserting a reactive functional group onto the molecular structure of this cyclophane is paramount for its inclusion into complex architectures. To this aim, including an alkyne moiety would be ideal, because it can participate in click reactions. However, the synthesis of such alkyne-functionalized cyclophane suffers from several drawbacks: the use of toxic and expensive CCl4, the need for high-pressure reactors, and overall low yield. We have revised the existing synthesis of this cyclophane derivative bearing an alkyne moiety, to overcome all these limitations. In particular, photochemical radical bromination is adopted to obtain a sensitive intermediate. We demonstrated that the synthesized host molecule can be functionalized via click reactions and take part in radical-radical interactions. Our work makes a key functionalized paraquat macrocycle more accessible, facilitating the development of novel redox-responsive systems

Endergonic synthesis of Diels-Alder adducts enables non-equilibrium adaptive behaviors in chemical reaction networks

The overwhelming majority of artificial chemical reaction networks respond to stimuli relaxing towards an equilibrium state. The opposite response – moving away from equilibrium – can afford the endergonic synthesis of molecules, of which only rare examples have been reported. Here, we report six examples of Diels-Alder adducts accumulated in an endergonic process and use this strategy to realize adaptive phenomena. Indeed, systems respond to repeated occurrences of the same stimulus by increasing the amount of adduct formed, with the final network distribution depending on the number and frequency of stimuli received. Our findings indicate how endergonic processes can contribute to the transition from responsive to adaptive systems

Solvent-Free Pd-Catalyzed Heteroaryl-Aryl Coupling via C-H Bond Activation for the Synthesis of Extended Heteroaromatic Conjugated Molecules

Direct arylation of thienopyrrolodione, diketopyrrolopyrroles, benzodithiophene derivatives, and fluorinated heteroarenes with functionalized aryl iodides is proven in solvent-free and non-anhydrous conditions. The reaction is performed in the presence of air and tolerates several functional groups on both the coupling partners, enabling a convenient synthesis of extended heteroaromatic conjugated molecules

Solvent-Free Pd-Catalyzed Heteroaryl–Aryl Coupling via C–H Bond Activation for the Synthesis of Extended Heteroaromatic Conjugated Molecules

Direct arylation of thienopyrrolodione, diketopyrrolopyrroles, benzodithiophene derivatives, and fluorinated heteroarenes with functionalized aryl iodides is proven in solvent-free and non-anhydrous conditions. The reaction is performed in the presence of air and tolerates several functional groups on both the coupling partners, enabling a convenient synthesis of extended heteroaromatic conjugated molecules