Efficient Generation of Stable Planar Cages for Chemistry

In this paper we describe an algorithm which generates all colored planar maps with a good minimum sparsity from simple motifs and rules to connect them. An implementation of this algorithm is available and is used by chemists who want to quickly generate all sound molecules they can obtain by mixing some basic components.Comment: 17 pages, 7 figures. Accepted at the 14th International Symposium on Experimental Algorithms (SEA 2015

Laboratory photo-chemistry of covalently bonded fluorene clusters: observation of an interesting PAH bowl-forming mechanism

The fullerene C$_{60}$, one of the largest molecules identified in the interstellar medium (ISM), has been proposed to form top-down through the photo-chemical processing of large (more than 60 C-atoms) polycyclic aromatic hydrocarbon (PAH) molecules. In this article, we focus on the opposite process, investigating the possibility that fullerenes form from small PAHs, in which bowl-forming plays a central role. We combine laboratory experiments and quantum chemical calculations to study the formation of larger PAHs from charged fluorene clusters. The experiments show that with visible laser irradiation, the fluorene dimer cation - [C$_{13}$H$_{9}$$-$C$_{13}$H$_{9}$]$^+$ - and the fluorene trimer cation - [C$_{13}$H$_{9}$$-$C$_{13}$H$_{8}$$-$C$_{13}$H$_{9}$]$^+$ - undergo photo-dehydrogenation and photo-isomerization resulting in bowl structured aromatic cluster-ions, C$_{26}$H$_{12}$$^+$ and C$_{39}$H$_{20}$$^+$, respectively. To study the details of this chemical process, we employ quantum chemistry that allows us to determine the structures of the newly formed cluster-ions, to calculate the hydrogen loss dissociation energies, and to derive the underlying reaction pathways. These results demonstrate that smaller PAH clusters (with less than 60 C-atoms) can convert to larger bowled geometries that might act as building blocks for fullerenes, as the bowl-forming mechanism greatly facilitates the conversion from dehydrogenated PAHs to cages. Moreover, the bowl-forming induces a permanent dipole moment that - in principle - allows to search for such species using radio astronomy.Comment: 8 pages, 7 figures, accepte

Complementarity and preorganisation in the assembly of heterometallic-organic cages via the metalloligand approach : recent advances

The design of new metallocage polyhedra towards pre-determined structures can offer both practical as well as intellectual challenges. In this mini-review we discuss a selection of recent examples in which the use of the metalloligand approach has been employed to overcome such challenges. An attractive feature of this approach is its stepwise nature that lends itself to the design and rational synthesis of heterometallic metal–organic cages, with the latter often associated with enhanced functionality

The topology of fullerenes

Fullerenes are carbon molecules that form polyhedral cages. Their bond structures are exactly the planar cubic graphs that have only pentagon and hexagon faces. Strikingly, a number of chemical properties of a fullerene can be derived from its graph structure. A rich mathematics of cubic planar graphs and fullerene graphs has grown since they were studied by Goldberg, Coxeter, and others in the early 20th century, and many mathematical properties of fullerenes have found simple and beautiful solutions. Yet many interesting chemical and mathematical problems in the field remain open. In this paper, we present a general overview of recent topological and graph theoretical developments in fullerene research over the past two decades, describing both solved and open problems. WIREs Comput Mol Sci 2015, 5:96–145. doi: 10.1002/wcms.1207 Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website

Rational Synthesis of Fullerenes

Fullerenes are a unique family of carbon-based cage molecules, which attract interest because of their remarkable properties and potential applications. Most effort so far has been focused on the study of C60 and C70, whereas other members of the huge fullerene family remain poorly explored. One of the main challenges in this field is the developing of the synthetic methods, which are suitable for the production of these unique materials in isomer-pure form in macroscopic amounts. Here, we review studies toward the rational synthesis of fullerenes from molecular precursors that have been published to date. The scope and limitation of the zipping strategy are discussed. The relevance and prospects for construction of the fullerene cages and related carbon-based nanostructures via cyclodehydrofluorination (C─F bond activation) are highlighted

Atomistic origins of high-performance in hybrid halide perovskite solar cells

The performance of organometallic perovskite solar cells has rapidly surpassed that of both conventional dye-sensitised and organic photovoltaics. High power conversion efficiency can be realised in both mesoporous and thin-film device architectures. We address the origin of this success in the context of the materials chemistry and physics of the bulk perovskite as described by electronic structure calculations. In addition to the basic optoelectronic properties essential for an efficient photovoltaic device (spectrally suitable band gap, high optical absorption, low carrier effective masses), the materials are structurally and compositionally flexible. As we show, hybrid perovskites exhibit spontaneous electric polarisation; we also suggest ways in which this can be tuned through judicious choice of the organic cation. The presence of ferroelectric domains will result in internal junctions that may aid separation of photoexcited electron and hole pairs, and reduction of recombination through segregation of charge carriers. The combination of high dielectric constant and low effective mass promotes both Wannier-Mott exciton separation and effective ionisation of donor and acceptor defects. The photoferroic effect could be exploited in nanostructured films to generate a higher open circuit voltage and may contribute to the current-voltage hysteresis observed in perovskite solar cells.Comment: 6 pages, 5 figure

Metastable exohedrally decorated Borospherene B-40

The experimental discovery of borospherene, the only non-carbon fullerene observed in nature, has generated a lot of interest in the scientific community and led to the theoretical prediction of various endohedrally and exohedrally decorated borospherene. We apply Minima Hopping Method (MHM), a global geometry optimization algorithm at the density functional level to check the stability of recently proposed exohedrally decorated borospherenes M6@B40 for (M = Li, Na, K, Rb, Be, Mg, Ca, Sr, Sc and Ti). By performing short MHM runs, we find that the proposed fullerene structures are not global minima. Our new lowest energy structures are significantly deformed and of much lower symmetry. These low energy structures spontaneously aggregate by forming chemical bonds when they are brought together. Therefore, it would be challenging to synthesize bulk materials made out of the theoretically postulated exohedrally decorated borospherenes such as B40M6 which might have technologically useful properties

Reactor R&D: Synthesis and Optimization of Metallic Nitride Fullerenes and the Introduction of Two New Classes of Endohedral Metallofullerenes, Metallic Nitride Azafullerenes and Oxo-metallic Fullerenes

Metallic nitride fullerenes (MNFs) were discovered in 1999. This class of endohedral fullerenes show promise in a new diverse range of useful applications. Since then, focus has shifted to the selective synthesis of these molecules with yields that would accommodate adequate sample distribution. Using the electric arc method, the traditional yield of these molecules has been very low (i.e. \u3c 5 mg), and only a small percentage of the fullerene products (i.e. \u3c 5%). This dissertation introduces the novel CAPTEAR (Chemically Adjusting Plasma Temperature, Energy, And Reactivity) method that allows the targeted synthesis of MNFs in high purity and yield. This method utilizes a nontraditional oxidizing method for fullerene synthesis that has not only provided optimization of MNFs, but also resulted in the discovery of two new classes of fullerenes: metallic nitride azafullerenes (MNAFs) and oxo-metallic fullerenes (OMFs). Evidence suggests that the nitrogen of the MNAF cage provides stability for the trimetallic nitride clusters, while the OMFs are the first fullerenes to encapsulate oxygen and incorporate a seven atom cluster inside a Cgo cage. Other efforts to increase yields resulted from scaling up production of fullerenes by using larger quantities of starting materials. These larger quantities required energy (electrical current) beyond the capacity of the traditional electric arc generator. Therefore, a new electric arc generator was designed and fabricated to accommodate these demands. This scale-up process resulted in yield increases by an average of 400%. However, to reduce the waste of scaling up as well as costs, our lab developed a recycling method for the expensive metal oxide starting materials. This method has greatly improved cost effectiveness and waste reduction