Synthesis, Characterization, and Modeling of Naphthyl-Terminated sp Carbon Chains: Dinaphthylpolyynes

Synthesis, structure, and properties of switchable cross-conjugated 1,4-diaryl-1,3-butadiynes based on 1,8-bis(dimethylamino)naphthalene

A set of novel 1,4-diaryl-1,3-butadiynes terminated by two 7-(arylethynyl)-1,8-bis(dimethylamino)naphthalene fragments was prepared via the Glaser-Hay oxidative dimerization of 2-ethynyl-7-(arylethynyl)-1,8-bis(dimethylamino)naphthalenes. The oligomers synthesized in this way are cross-conjugated systems, in which two conjugation pathways are possible: π-conjugation of 1,8-bis(dimethylamino)naphthalene (DMAN) fragments through a butadiyne linker and a donor-acceptor aryl-C≡C-DMAN conjugation path. The conjugation path can be "switched" simply by protonation of DMAN fragments. X-ray diffraction, UV-vis spectroscopy and cyclic voltammetry are applied to analyze the extent of π-conjugation and the efficiency of particular donor-acceptor conjugation path in these new compounds. X-ray structures and absorption spectra of doubly protonated tetrafluoroborate salts of the oligomers are also discussed.

Nano-Hybrid Ag@LCCs Systems with Potential Wound-Healing Properties

The synthesis of contaminant-free silver@linear carbon chains (Ag@LCCs) nanohybrid systems, at different Ag/LCCs ratios, by pulsed laser ablation was studied. The ablation products were first characterized by several diagnostic techniques: conventional UV-Vis optical absorption and micro-Raman spectroscopies, as well as scanning electron microscopy, operating in transmission mode. The experimental evidence was confirmed by the theoretical simulations' data. Furthermore, to gain a deeper insight into the factors influencing metal@LCCs biological responses in relation to their physical properties, in this work, we investigated the bioproperties of the Ag@LCCs nanosystems towards a wound-healing activity. We found that Ag@LCC nanohybrids maintain good antibacterial properties and possess a better capability, in comparison with Ag NPs, of interacting with mammalian cells, allowing us to hypothesize that mainly the Ag@LCCs 3:1 might be suitable for topical application in wound healing, independent of (or in addition to) the antibacterial effect.

A new family of 1,4-diaryl-1,3-butadiynes based on the “proton sponge”: synthesis, electronic and chemical properties

A new family of 1,4-diaryl-1,3-butadiynes containing two and four fragments of 1,8-bis(dimethylamino)naphthalene (“proton sponge”) were synthesized.

Helical Molecular Orbitals to Induce Spin-Orbit Coupling in Oligoyne-Bridged Bifluorenes

Singlet-Triplet energy exchange is an area of active research due to its role in optoelectronic devices and photodynamic therapy. Large spin-orbit coupling (SOC) is difficult to achieve in simple hydrocarbon structures limiting the intersystem crossing (ISC) rates. A new approach to enhance the spin-orbit coupling via helical molecular orbitals is investigated in oligoyne-bridged bifluorenes. Transient absorption studies showed a singlet-to-triplet ISC rate of up to 6 ns^-1 resulting in 0.84 triplet yield. Density functional calculations revealed a direct relation between high ISC and large SOC values mediated by helical molecular orbitals. Calculations and spectroscopic data also suggested that El-Sayed forbidden ISC occurs as a direct transition between ¹ππ* and ³ππ*, which becomes allowed due to a symmetry-breaking interaction leading to mixing between orthogonal π-systems in the oligoyne fragment.

Carbon sp chains in diamond nanocavities

We propose a new class of carbon allotropes obtained by combining linear sp carbon chains with sp3 bulk carbon. The structure of these crystalline carbon allotropes consists of sp chains inserted in cylindrical cavities periodically arranged in hexagonal diamond (lonsdaleite). We carry out a detailed computational analysis of the structural, electronic, and vibrational properties of a simple form in this class: a single C6 strand embedded in a nm-sized cavity. We obtain a metallic allotrope exhibiting characteristic high-frequency vibrations associated with the sp chain stretching modes, and characterized by long-time room-temperature stability. In addition, we suggest how numerous similar allotropes could be constructed within this class, that we call zayedenes, all characterized by comparable metallicity and high-frequency vibrations.

Exploiting Unsaturated Carbon-Iodine Compounds for the Preparation of Carbon-Rich Materials

Conjugated carbon-rich materials have drawn much academic and industrial attention in recent years, due to their intriguing electronic and optical properties and potential applications including organic photovoltaics, flexible and wearable electronics, and chemical and biological sensors. Unsaturated carbon-iodine compounds, mainly the derivatives of iodoalkenes and iodoalkynes, are a class of molecules in which iodine atoms are directly connected to unsaturated carbons. These compounds provide unique advantages in the pursuit of carbon-rich materials, largely due to the Lewis acidity of iodine atoms and the lability of the carbon-iodine bonds. The Lewis acidity and electrophilicity of iodine in unsaturated carbon-iodine compounds make them excellent donors of halogen bonding, which is an attractive interaction between the electrophilic halogen atoms and Lewis basic species. Halogen bonding has emerged as a reliable building block in crystal engineering and supramolecular architectures. In this Account, we illustrate examples of the controlled assembly of diiodopolyynes within host-guest cocrystals that contain oxalamide or urea hosts with appropriate Lewis basic end groups and diiodobutadiyne or diiodohexatriyne guests. Halogen bonding interactions between the host and guest result in an ordered alignment of the diiodopolyynes that allows for a solid-state topochemical polymerization. We have used this approach to prepare poly(diiododiacetylene), PIDA, and poly(iodoethynyliododiacetylene), PIEDA, two conjugated polymers composed only of carbon and iodine. In addition, the polarity of the carbon-iodine bond gives unsaturated carbon-iodine compounds an electron-rich π-system, permitting electrophilic addition reactions with molecular halogens. The halogenated products of these additions can then serve as precursors to other conjugated carbon-rich systems. The lability of the carbon-iodine bond, together with the polarizability of iodine and the higher electronegativity of sp- and sp²-hybridized carbons, open up further possibilities in pursuing novel carbon nanomaterials from unsaturated carbon-iodine compounds. For example, we have developed an iterative method for the synthesis of longer symmetric polyynes from shorter diiodopolyynes, using Stille coupling to the iodine-capped polyynes. The iodination/coupling cycle symmetrically lengthens the polyyne chain by two carbon-carbon triple bonds. This method is particularly helpful for preparing polyynes with an odd number of carbon-carbon triple bonds. In addition, the lability of the carbon-iodine bonds of PIDA leads to facile carbonization by pyrolysis or laser irradiation. More strikingly, diiodoalkenes undergo quantitative elimination of iodine in the presence of Lewis bases. This reaction can be used to eliminate iodine at room temperature from PIDA, in which the carbon-iodine bonds are much more easily broken than in the diiodopolyynes, resulting in graphitic carbon materials.

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

Novamene: A new class of carbon allotropes

We announce a new class of carbon allotropes. The basis of this new classification resides on the concept of combining hexagonal diamond (sp³ bonded carbon − lonsdaleite) and ring carbon (sp² bonded carbon − graphene). Since hexagonal diamond acts as an insulator and sp² bonded rings act as conductors, these predicted materials have potential applications for transistors and other electronic components. We describe the structure of a proposed series of carbon allotropes, novamene, and carry out a detailed computational analysis of the structural and electronic properties of the simplest compound in this class: the single-ring novamene. In addition, we suggest how hundreds of different allotropes of carbon could be constructed within this class.

Polymerization of acetylene: polyynes, but not carbyne

Polymerization of acetylene in the presence of sterically-hindered endgroups leads to polyynes, but with lengths shorter than by stepwise syntheses.

Massive dihydrogen uptake by anionic carbon chains

The remarkable capacity of anionic and dianionic carbon chains to bind dihydrogen compared to their neutral moieties has been established theoretically and these one dimensional anions could be utilized in developing novel H₂ storage materials.

Carbon-atom wires: 1-D systems with tunable properties

This review provides a discussion of the current state of research on linear carbon structures and related materials based on sp-hybridization of carbon atoms (polyynes and cumulenes). We show that such systems have widely tunable properties and thus represent an intriguing and mostly unexplored field for both fundamental and applied sciences. We discuss the rich interplay between the structural, vibrational, and electronic properties focusing on recent advances and the future perspectives of carbon-atom wires and novel hybrid sp-sp(2)-carbon architectures.

Non-covalent intermolecular carbon-carbon interactions in polyynes

Polyynes, the smaller analogues of one dimensional infinite chain carbon allotrope carbyne, have been studied for the type and strength of the intermolecular interactions in their dimer and tetramer complexes using density functional theory. The nature of end group functionalities and the chain length of the polyynes are varied to assess their role in modulating the non-covalent interaction energy. As seen in molecular electrostatic potential analysis, all the polyyne complexes showed a multitude of non-covalent CC interactions, resulting from complementary electrostatic interactions between relatively electron rich formal triple bond region of one monomer and the electron deficient formal single bond region of the other monomer. This type of paired (C[triple bond, length as m-dash]C)(C-C) bonding interaction, also characterized using quantum theory of atoms-in-molecules, increases with increase in the monomer chain length leading to substantial increase in interaction energy (Eint); -1.07 kcal mol(-1) for the acetylene dimer to -45.83 kcal mol(-1) for the 50yne dimer. The magnitude of Eint increases with substitutions at end positions of the polyyne and this effect persists even up to 50 triple bonds, the largest chain length analyzed in this paper. The role of CC interactions in stabilizing the polyyne dimers is also shown by sliding one monomer in a dimer over the other, which resulted in multiple minima with a reduced number of CC interactions and lower values of Eint. Furthermore, strong cooperativity in the CC bond strength in tetramers is observed as the interaction energy per monomer (Em) of the polyyne is 2.5-2.8 times higher compared to that of the dimer in a test set of four tetramers. The huge gain in energy observed in large polyyene dimers and tetramers predicts the formation of polyyne bundles which may find use in the design of new functional molecular materials.

A systematic study on the Cadiot–Chodkiewicz cross coupling reaction for the selective and efficient synthesis of hetero-diynes

99% selectivity for cross coupling. Excellent yields (upto 94%). Low basic reaction medium, high functional group tolerance. Use of green solvent water.

Electron transport in carbon wires in contact with Ag electrodes: a detailed first principles investigation

The structure and electronic properties of carbon atom chains C_n in contact with Ag electrodes are investigated in detail with first principles means.

Recent developments and applications of the Cadiot–Chodkiewicz reaction

The classical heterocoupling of a 1-haloalkyne with a terminal alkyne catalyzed by copper salts in the presence of a base for the synthesis of unsymmetrical diynes is termed the Cadiot–Chodkiewicz coupling reaction.

Thermal formation of carbynes

We simulate the formation of sp carbon chains (carbynes) by thermal decomposition of sp(2) carbon heated by a hot discharge plasma, by means of tight-binding molecular dynamics. We obtain and analyze the total quantity of carbynes and their length distribution as a function of temperature and density.

Carbon sp chains in graphene nanoholes

Nowadays sp carbon chains terminated by graphene or graphitic-like carbon are synthesized routinely in several nanotech labs. We propose an ab initio study of such carbon-only materials, by computing their structure and stability, as well as their electronic, vibrational and magnetic properties. We adopt a fair compromise of microscopic realism with a certain level of idealization in the model configurations, and predict a number of properties susceptible to comparison with experiment.

Vibrational characterization of dinaphthylpolyynes: a model system for the study of end-capped sp carbon chains

We perform a systematic investigation of the resonance and vibrational properties of naphthyl-terminated sp carbon chains (dinaphthylpolyynes) by combined multi-wavelength resonant Raman (MWRR) spectroscopy, ultraviolet-visible spectroscopy, and Fourier-transform infrared (FT-IR) spectroscopy, plus ab initio density functional theory (DFT) calculations. We show that the MWWR and FT-IR spectroscopies are particularly suited to identify chains of different lengths and different terminations, respectively. By DFT calculations, we further extend those findings to sp carbon chains end-capped by other organic structures. The present analysis shows that combined MWRR and FT-IR provide a powerful tool to draw a complete picture of chemically stabilized sp carbon chains.