Fullerene Fragments Research Articles

APPLICATION OF OPTIMIZATION METHOD IN MULTIDIMENSIONAL SPACE TO THE PROBLEM OF DETERMINING FULLERENE CONCENTRATION IN FULLERENE-CONTAINING MIXTURE

The work proposes a method for the quantitative processing of experimental data from ultraviolet spectroscopy of substituted fullerene mixtures, taking into account errors in the experimental data. This task can be written as a system of Vierordt equations (a system of linear equations). The coefficients of the system are the extinction coefficients of individual substituted fullerenes, which are difficult to measure accurately. Therefore, the mathematical model of the problem contains significant errors that affect the reliability and stability of the solution. To minimize the influence of errors, the work [1] proposes a method, which involves reducing the considered system of linear equations to a linear programming problem. This study generalizes the work [1] and proposes to use linear programming problems to find interval values of correction factors for parameters containing errors. Since decreasing the discrepancy reduces the solution error only for well-conditioned coefficient matrices, the values of correction coefficients that minimize the condition number of the coefficient matrix are found in the obtained intervals. The found correction values allowed to significantly improve the conditionality of the system coefficient matrix and obtain a more accurate solution. By using the refined extinction coefficients, the distribution of molar fractions of fullerene fragments and fullerene-containing compounds in the mixture of products formed by the attachment of cyanoisopropyl radicals was obtained, as well as the distribution of molar fractions of fullerene fragments of different degrees of substitution for samples of fullerene-containing polymethyl methacrylate and the distribution of molar fractions of fullerene fragments of different degrees of substitution for samples of fullerene-containing polystyrene. The results are correct and consistent with the theory, both for low-molecular-weight mixtures and for fullerene-containing polymers.

Theoretical description of photoinduced electron transfer in donor-acceptor supramolecular complexes based on carbon buckybowls.

Herein, we explore, from a theoretical perspective, the nonradiative photoinduced processes (charge separation and energy transfer) within a family of donor-acceptor supramolecular complexes based on the electron-donor truxene-tetrathiafulvalene (truxTTF) derivative and a series of curved fullerene fragments (buckybowls) of different shapes and sizes (C30H12, C32H12, and C38H14) as electron acceptors that successfully combine with truxTTF via non-covalent interactions. The resulting supramolecular complexes (truxTTF·C30H12, truxTTF·C32H12, and truxTTF·C38H14) undergo charge-separation processes upon photoexcitation through charge-transfer states involving the donor and acceptor units. Despite the not so different size of the buckybowls, they present noticeable differences in the charge-separation efficiency owing to a complex decay post-photoexcitation mechanism involving several low-lying excited states of different natures (local and charge-transfer excitations), all closely spaced in energy. In this intricate scenario, we have adopted a theoretical approach combining electronic structure calculations at (time-dependent) density functional theory, a multistate multifragment diabatization method, the Marcus-Levitch-Jortner semiclassical rate expression, and a kinetic model to estimate the charge separation rate constants of the supramolecular heterodimers. Our outcomes highlight that the efficiency of the photoinduced charge-separation process increases with the extension of the buckybowl backbone. The supramolecular heterodimer with the largest buckybowl (truxTTF·C38H14) displays multiple and efficient electron-transfer pathways, providing a global photoinduced charge separation in the ultrafast time scale in line with the experimental findings. The study reported indicates that modifications in the shape and size of buckybowl systems can give rise to attractive novel acceptors for potential photovoltaic applications.

Giant nonlinear optical response of fullerene polymer fragments: a DFT perspective

Organic π-conjugated materials exhibit exceptional nonlinear optical (NLO) properties due to their unique electronic structures, characterized by short response times and large NLO responses. Fullerene (C60) is one of the few polymer species that possess a rich π-conjugated system, making it a promising material with significant NLO responses. In the present paper, we designed three C60 polymer fragments and employed density functional theory to estimate their molecular static first and second hyperpolarizabilities. Compared to previously reported fullerene derivatives, the designed C60 polymer fragments can exhibit notable second-order and third-order molecular NLO responses. The study shows that the hyperpolarizabilities and energy gaps of the investigated C60 polymer fragments are greatly influenced by their topological structures and bonding modes. These findings provide new insights for the design of novel NLO materials based on C60 polymers, and the realization of tunable NLO responses in C60 cluster-based molecular systems, which may have significant applications in nanophotonic devices.

C3-Symmetric Indole-Based Truxenes: Design, Synthesis, and Photophysical Studies.

In recent years, truxenes and related polyaromatic hydrocarbons (PAHs) have engrossed ample interest of the scientific community because of their ease of synthesis, functionalizations, and use as building blocks for the synthesis of fullerene fragments, liquid crystals, larger polyarenes, and C3-tripod materials. In the present work, we have disclosed an ingenious method for the construction of various indolo-truxene hybrid molecules in good yields (52-90%), by means of the acid-catalyzed cotrimerization, Friedel-Crafts acylation, and Fischer indole synthesis, and fully characterized them through the standard spectroscopic techniques. The photophysical properties of the thus-prepared compounds have also been investigated using steady-state absorption and fluorescence and time-resolved fluorescence spectroscopy techniques. Moreover, the density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been studied to correlate them with the measured photophysical properties of the synthesized indolo-truxene derivatives.

Nanographenes Out of Planarity

AbstractThe combination of different distortion motifs in nanographenes and polycyclic conjugated hydrocarbons has been the focus of significant attention during the last decade. The continual discovery of multiple carbon allotropes has fueled the field. A plethora of research groups around the globe are engaged in developing methods for the preparation of discrete graphene or fullerene fragments and new carbon allotropes. The goal is to fully understand the structure–property relationships in these systems. Herein, we present our journey and contributions to the field, from the development of a synthetic methodology towards functionalized heptagon-containing hexa-peri-hexabenzocoronenes through the preparation of saddle-helix hybrid nanographenes, the study of heptagon-containing cumulenic and open-shell systems, nanographenes embedded with higher order carbocycles, and the study of their electronic properties on-surface and by single-molecule conductance.1 Introduction2 The Finding of a Cornerstone Scaffold3 Saddle-Helix Hybrid Nanographenes4 Cumulenic and Diradicaloid Systems5 Supramolecular Studies6 Octagon- and Nonagon-Embedded Nanographenes7 Molecular Electronics and On-Surface Studies8 Outlook

Novel organic semiconductor materials combined by sumanene and corannulene: Rational functionalization based on the electronic structures of highly curved buckybowl

Due to the unique optoelectronic properties of bowl-shaped structural materials such as the fullerene fragments corannulene and sumanene, which are widely used in electronic devices, it is important to study their electronic structures in more detail. To this end, we have carried out detailed modeling and computational studies of the electronic structures of highly curved bowl-shaped molecules containing corannulene and sumanene fragments via DFT calculations. Our aim was to investigate whether topological recombination of different buckybowl fragments could multiply their advantages and improve our understanding of these materials at the genetic level. This work has mainly expanded the study from single-molecule photoelectric properties to the crystal transport properties. First, the structural and optoelectronic properties of C- and S-series monomer molecules by theoretical calculations from several aspects, such as bowl depths, frontier molecular orbitals, ionization potentials, electron affinities, reorganization energies, the absorption spectra in vacuum and the energy difference between the singlet and triplet state were described in detail, furthering the understanding of individual fragments. Then, the investigation of the potential charge transport properties of the crystals according to the quantum nuclear tunneling model using the dimer model is to be carried out in order to provide a deeper understanding of the application of molecule whole in organic semiconductor materials. Monte Carlo simulation was used to obtain the diffusion constant, and the Einstein equation was applied to obtain the carrier mobility. This study provides a deep understanding of the intrinsic properties of the highly curved bowl-shape polycyclic aromatic hydrocarbons. What's more, it reveals that perpendicular columnar stacking crystals can be excellent candidate used for novel organic semiconductor materials. © 2023 Elsevier Science. All rights reserved.

Mechanical and Electronic Properties of a Carbon-Composite 3D Nanomaterial with an Island-Type Topology

An atomistic model of a carbon-composite 3D nanomaterial with an island-type topology based on fullerene and graphene fragments as well as chiral/achiral single-walled carbon nanotubes (SWCNTs) with a subnanometer diameter is constructed. The island type refers to the presence of inhomogeneously distributed local regions with increased density of the nanomaterial in the structure of the composite. The effect of the concentration of nanotubes in the composite on the volume compressibility and electronic properties is investigated. It is found that an increase in the mass fraction of SWCNTs in the composite leads to a decrease in the coefficient of volume compressibility and, at the same time, improvement in the conductive properties. Classical molecular dynamics and the density functional based tight binding (DFTB) method with the use of dispersive energy correction are used for the physically correct description of individual fragments of the composite which are not covalently bound.

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

Air Stable Chalcogen-Doped Rubicenes with Diradical Character

Air Stable Chalcogen-Doped Rubicenes with Diradical Character

Using fullerene fragments as acceptors to construct thermally activated delayed fluorescence emitters for high-efficiency organic light-emitting diodes

Fragments of fullerene are used as acceptor segments for the first time to construct two thermally activated delayed fluorescence (TADF) compounds DBCP and FAP. Both compounds exhibit similar highly twisted geometries and separated frontier molecular orbital distributions. While on the other hand, their locally exited triplet energy levels from acceptor moieties (3LEA) are fine-tunable owning to the different structural stress in the fragments, resulting in different lowest triplet excited state (T1) features. In DBCP, the 3LEA is the high lying state and thus DBCP exhibits a small singlet–triplet energy difference of 0.10 eV and a high photoluminescence quantum yield (ΦPL) of 89% with excellent TADF characteristics; while T1 of FAP is 3LEA, and thus, FAP displays poor triplet exciton utilization with ΦPL of only 54%. In organic light-emitting diodes (OLEDs) based on DBCP and FAP as dopants, maximum external quantum efficiencies of 20.2% and 12.8% are respectively achieved. This work not only demonstrates for the first time that fullerene fragments can be used as key building blocks for TADF emitters, it also proves in principle that pure hydrocarbon mobilities without any electronegative heteroatom can also be employed as acceptor segment in high performance TADF emitters.

Embedding Heteroatoms and Adjacent Pentagons in Concave Molecules

Bowl-shaped molecules, which can be viewed as fragments of fullerenes, have been extensively studied owing to their interesting fundamental properties derived from their unique geometry, and the possibilities for their further functionalization, with potential applications in the field of materials science. Most of the reported concave compounds are based on corannulene or sumanene, the simplest representative fullerene subunits possessing isolated pentagons. Syntheses of concave molecules bearing adjacent pentagons have rarely been reported. Inspired by the structure of N-heterotriangulene, the construction of bowl-shaped compounds containing two fused pentagons and a central nitrogen atom is discussed. Further surface extension of such concave molecules can result in the formation of boat-shaped compounds containing embedded double isolated nitrogen atoms.

Rational Functionalization of a C70 Buckybowl To Enable a C70:Buckybowl Cocrystal for Organic Semiconductor Applications.

Fullerene fragments, referred to as buckybowls, are garnering interest due to their distinctive molecular shapes and optoelectronic properties. Here, we report the synthesis and characterization of a novel C70 subunit, diindeno[4,3,2,1-fghi:4',3',2',1'-opqr]perylene, that is substituted with either triethylsilyl(TES)-ethynyl or 2,4,6-triisopropylphenyl groups at the meta-positions. The resulting compounds (1 and 2) display a bowl-to-bowl inversion at room temperature. Notably, the substituent groups on the meta-positions alter both the geometric and the electronic properties as well as the crystal packing of the buckybowls. In contrast to the 2,4,6-triisopropylphenyl groups in 2, the TES-ethynyl groups in 1 lead to enhanced bond length alternation, resulting in weaker aromaticity of the six-membered rings of the buckybowl skeleton. 1 forms one-dimensional (1D) concave-in-convex stacking columns, and when 1 is blended with C70, the buckybowls encapsulate C70 and result in two-dimensional cocrystals. Organic field-effect transistor (OFET) measurements demonstrate that 1 displays a hole mobility of 0.31 cm2 V-1 s-1, and the 1-C70 cocrystal exhibits ambipolar transport characteristics with electron and hole mobilities approaching 0.40 and 0.07 cm2 V-1 s-1, respectively. This work demonstrates the potential of buckybowls for the development of organic semiconductors.

Optical Spectroscopy of Small Carbon Clusters from Electron-Impact Fragmentation and Ionization of Fullerene-C60.

A series of cationic molecular fragments (C n+, n = 11, 12, 15, 16, 18, and 21), produced by electron-impact ionization of C60 in the gas phase, were each mass-selected and accumulated in cryogenic Ne matrices. Optical absorption measurements in the UV-vis and IR spectral ranges reveal linear carbon chain structures. In particular, we have observed the known electronic transitions of linear C11, C15, and C21. The NIR transitions of linear C15-, C16-, and C18- have also been detected, indicating that soft-landing of the corresponding cations can also involve charge-changing. Newly observed electronic absorptions at 410.3 and 429.9 nm have been assigned to linear C18 absorptions at 438.2, 443.5, 422.3, and 433.7 nm, to linear C15+, and absorption at 395.5 nm, to linear C16. Increasing deposition energy leads to fragmentation upon impact. This is indicated by absorptions of C10 (313, 316.3 nm), when depositing C n+ ( n = 11, 15, 16) as well as C12 (332 nm) or C14 (347.4, 356.6 nm), when depositing C15+ or C16+, respectively. These were previously assigned to cyclic isomers. We reassign them to linear isomers here on the basis of plausibility arguments. The observations have been supported by time-dependent density functional theory calculations for ring and chain isomers of C n+/-/0, 10 ≤ n ≤ 20 up to the vacuum-UV range. The electronic absorptions of carbon chains are at least 1 order of magnitude stronger than all NIR electronic absorptions of C60+, which have recently been attributed to several of the diffuse interstellar bands. Considering that fullerene multifragmentation yields long carbon chains that have very strong absorptions both in the UV-vis and IR spectral regions, these systems appear to be good candidates to be observed in regions of space containing fullerenes.

Photogalvanic eff ect in porphyrin-pyrrolo[3′,4′:1,9]-(C60-Ih)[5,6]fullerene-2′,5′-dicarboxylate systems

The influence of molecular structural factors of covalently bound porphyrin-fullerene dyads and porphyrin—fullerene binary mixtures on photocurrent in model photoelectrochemical cells was studied. It was found that the photocurrent increased either by introducing solubilizing alkyl groups into the donor (porphyrin) or acceptor (fullerene) fragments, or by covalent binding porphyrin and fullerene into a donor-acceptor dyad.

Carbon fragments as highly active metal-free catalysts for the oxygen reduction reaction: a mechanistic study.

In metal-free carbon-fullerene-based or defective graphene-based electrocatalysts, pentagon rings are known to play a key role in boosting catalytic activities for the oxygen reduction reaction (ORR). However, the fundamental chemical mechanism underlying the remarkable catalytic effect of the pentagon rings towards the ORR is still not fully understood. Herein, we perform a comprehensive computational study of the catalytic activities of various carbon fullerenes and fullerene fragment species, all containing pentagon rings, by using the density functional theory (DFT) and computational hydrogen electrode (CHE) methods. We find that more active sites on carbon are associated with more neighbouring pentagon rings and stronger adsorption of the key intermediates of O*, OH* and OOH* for the ORR. Importantly, two C60-based fragments, namely, C60-frag1 and C60-frag2l, show a very high activity towards the ORR, as both yield overpotentials as low as 0.389 and 0.407 V, and entail suitable adsorption free energy of OH* and OOH* species. These desirable chemical properties of fullerene fragments can be attributed to the high-energy HOMO orbitals, induced by the low-symmetry fullerene-fragment structures. Both the number of neighbouring pentagon rings and the degree of overall symmetry of the fragment appear to be the two important factors that can be adjusted for the design of optimal metal-free carbon electrocatalysts towards high ORR activities.

Record Alkali Metal Intercalation by Highly Charged Corannulene.

The need for advanced energy storage technologies demands the development of new functional materials. Novel carbon-rich and carbon-based materials of different structural topologies attract significant attention in this regard. Attractive systems include a unique class of bowl-shaped polycyclic aromatic hydrocarbons that map onto fullerene surfaces and are thus often referred to as fullerene fragments, buckybowls, or π-bowls. Importantly, carbon bowls are able to acquire multiple electrons in stepwise reduction reactions producing sets of successively reduced carbanions. The resulting negatively charged π-bowls exhibit unique supramolecular assembly and metal intercalation patterns that only recently have begun to be uncovered. First, we have resolved the long-standing mystery behind the supramolecular structure formed by a highly reduced fullerene fragment called corannulene (C20H104-) with multiple lithium ions, using X-ray crystallography coupled with NMR spectroscopy and theoretical calculations. This work provided a new paradigm for lithium ion intercalation between the curved carbon π-surfaces and facilitated understanding of the lithium ion storage mechanism in carbonaceous matrices. Next, we have initiated a new research direction, an investigation of the mixed alkali metal reduction reactions using bowl-shaped corannulene as a remarkable multielectron reservoir and unique ligand with open convex and concave π-surfaces. As a result, we have revealed the cooperative effect of lithium with heavier Group 1 metals in reduction and self-assembly processes of corannulene. Moreover, we have discovered a new class of organometallic supramolecules having heterometallic cores with high nuclearity and charge such as Li3M36+ and LiM56+ (M = K, Rb, and Cs) sandwiched between two tetrareduced corannulene decks. The resulting triple-decker supramolecular assemblies, fully characterized by X-ray diffraction and spectroscopic methods, were found to exhibit a record ability of the highly charged corannulene π-surfaces to be fully engaged in intercalation of multiple metal ions. Based on this unique ability, curved π-ligands with extended carbon frameworks are expected to show remarkable potential for alkali metal storage compared to flat polycyclic arenes. Notably, a previously unseen mode of internal lithium binding revealed in the heterobimetallic sandwiches is accompanied by unprecedented negative shifts (up to -25 ppm) in 7Li NMR spectra. Based on in-depth analysis of NMR data, augmented by DFT calculations, we have rationalized the observed experimental trends and proposed the mechanism of stepwise alkali metal substitution reactions. Furthermore, we have correlated the origin of the record 7Li NMR shifts with unique electronic structures of these novel supramolecular aggregates. Herein we present comprehensive analysis of unusual structural and electronic features of remarkable heterometallic self-assemblies formed by tetrareduced corannulene, using a wealth of our recent experimental and computational results. This work uncovers unique potential of highly negatively charged bowl-shaped π-ligands for new supramolecular chemistry and materials chemistry applications.

(Invited) Growth of Fullerene Fragments Using the Diels-Alder Cycloaddition Reaction

Density Functional Theory has been used to model the Diels-Alder reactions of the fullerene fragments triindenetriphenilene and pentacyclopentacorannulene with ethylene and 1,3-butadiene. The purpose is to prove the feasibility of using Diels-Alder cycloaddition reactions to grow fullerene fragments step by step, and to dimerize fullerene fragments, as a way to obtain C60. The dienophile character of the fullerene fragments is dominant, and the reaction of butadiene with pentacyclopentacorannulene is favored.

Quantum-Chemical Insights into the Self-Assembly of Carbon-Based Supramolecular Complexes.

Understanding how molecular systems self-assemble to form well-organized superstructures governed by noncovalent interactions is essential in the field of supramolecular chemistry. In the nanoscience context, the self-assembly of different carbon-based nanoforms (fullerenes, carbon nanotubes and graphene) with, in general, electron-donor molecular systems, has received increasing attention as a means of generating potential candidates for technological applications. In these carbon-based systems, a deep characterization of the supramolecular organization is crucial to establish an intimate relation between supramolecular structure and functionality. Detailed structural information on the self-assembly of these carbon-based nanoforms is however not always accessible from experimental techniques. In this regard, quantum chemistry has demonstrated to be key to gain a deep insight into the supramolecular organization of molecular systems of high interest. In this review, we intend to highlight the fundamental role that quantum-chemical calculations can play to understand the supramolecular self-assembly of carbon-based nanoforms through a limited selection of supramolecular assemblies involving fullerene, fullerene fragments, nanotubes and graphene with several electron-rich π-conjugated systems.

Evolution of glassy carbon under heat treatment: correlation structure\u2013mechanical properties

In order to accommodate an increasing demand for glassy carbon products with tailored characteristics, one has to understand the origin of their structure-related properties. In this work, through the use of high-resolution transmission electron microscopy, Raman spectroscopy, and electron energy loss spectroscopy it has been demonstrated that the structure of glassy carbon at different stages of the carbonization process resembles the curvature observed in fragments of nanotubes, fullerenes, or nanoonions. The measured nanoindentation hardness and reduced Young’s modulus change as a function of the pyrolysis temperature from the range of 600–2500 °C and reach maximum values for carbon pyrolyzed at around 1000 °C. Essentially, the highest values of the mechanical parameters for glassy carbon manufactured at that temperature can be related to the greatest amount of non-planar sp2-hybridized carbon atoms involved in the formation of curved graphene-like layers. Such complex labyrinth-like structure with sp2-type bonding would be rigid and hard to break that explains the glassy carbon high strength and hardness.

Giant fullerene formation through thermal treatment of fullerene soot

Coalescence of fullerenes into giant fullerenes (Cn n > 100) has been observed in the gas phase and inside carbon nanotubes. In this work, we demonstrate the formation of giant fullerenes by heating fullerene soot. Extracting the majority of the magic number fullerenes (C60 and C70) allowed the underlying distribution of fullerenes in the solid state to be measured. Upon heating at 800–1000 °C for 30–60 min under vacuum the mass distribution of fullerenes was found to shift toward larger masses. High resolution electron microscopy was used to compare formation of giant fullerenes by thermal heating and electron beam irradiation, showing the former produced more isolated giant fullerene fragments >1 nm in size. The driving force for coalescence and growth by thermal heating was suggested to be vertex strain at pentagonal sites, providing a route towards the synthesis of fullerenes up to C300.