Potential molecular semiconductor devices: cyclo-C_n (n = 10 and 14) with higher stabilities and aromaticities than acknowledged cyclo-C₁₈

Abstract

The successful isolation of cyclo-C18 in experiment means the ground-breaking epoch of carbon rings. Herein, we studied the thermodynamic stabilities of cyclo-Cn (4 ≤ n ≤ 34) with density functional theory. When n = 4N + 2 (N is integer), cyclo-Cn (10 ≤ n ≤ 34) were thermodynamically stable. Especially, cyclo-C10 and cyclo-C14 were thermodynamically, kinetically, dynamically, and optically preferred to cyclo-C18, and were the candidates of zero-dimension carbon rings. The carbon atoms were sp hybridization in cyclo-C10, cyclo-C14 and cyclo-C18. Cyclo-C14 and cyclo-C18 had alternating abnormal single and triple bonds, but cyclo-C10 had equal bonds.Cyclo-C10, cyclo-C14 and cyclo-C18 with large aromaticities had out-plane and in-plane π systems, which were perpendicular to each other. The number of π electrons in out-plane and in-plane π systems followed Hückel rule. Simulated UV-vis-NIR spectra indicated the similar electronic structures of cyclo-C14 and cyclo-C18. IntroductionThe carbon atom attracts a great deal of attentions because it is a fundamental atom in organic compounds and is the constituent atom for many useful materials. For example, there are some pure carbon materials, including zero-dimension fullerenes, [1] one-dimension nanotube, [2] two-dimension graphene, [3] and three-dimension diamond [4] and graphite. They are well-known as the allotropes of carbon atom and are useful in many fields due to their unique electronic structures and physical chemical features. In the past, fullerene is the only zero-dimension allotrope of carbon.Very recently, the successful synthesis and isolation of cyclo-C18 are epoch-making in the carbon chemistry and mean a second zero-dimension allotrope of carbon atom. [5] In fact, the early experiments on pure carbon clusters date back to 1954 using a heated substrate as cluster source. [6] After that, there are several experimental and theoretical studies on the cyclo-Cn. The synthesis and x-ray crystal structure of a direct precursor of cyclo-C18 were described in 1989. The results of time-of-flight mass spectroscopy recognized cyclo-C18 as the predominant fragmentation pattern with the flash heating experiments on this precursor. [7] In addition, Tobe and Diederich et al. synthesized a number of precursors of cyclo-C18 with well-defined cyclic geometries and readily removable groups. These precursors eventually generated cyclo-C18 by laser desorption induced [4 + 2] cycloreversion (retro-Diels-Alder reaction), decarbonylation or [2 + 2] cycloreversion. [8,9] . Rubin revealed that cyclo-C18 can be highly stabilized as a ligand in complex characterized by X-ray crystallography. [10] Furthermore, the mass spectral evidences of C18 are clearly detected during studying the fullerene-formation mechanism. [11] For example, the coalescence of cyclo-C30 predominantly produces buckminsterfullerene (C60), and the small rings cyclo-C18 and cyclo-C24 preferentially produce fullerene C70 through distinct intermediates. [11] The electronic spectra of C18 and C22 were detected in the ...

Remarkable Size Effect on Photophysical and Nonlinear Optical Properties of All‐Carboatomic Rings, Cyclo[18]carbon and Its Analogues

“…Cyclo [18]carbon (C 18 ), a closed-loop polyyne of 18 sp-hybridized carbon atoms joined together, is one of the hottest molecule recently. Due to its unique molecular geometry and electronic structure, C 18 has quickly attracted extensive attentions from chemists after being generated and observed in condensed phase in 2019 1 and soon received wide investigations [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . Our group has also made a series of theoretical studies on it, including aromaticity, optical properties, intermolecular interaction, vibrational spectra, and so on [19][20][21][22][23] .…”

TAO-DFT investigation of electronic properties of linear and cyclic carbon chains

“…On the other hand, cyclic carbon chains (for brevity, denoted as c-CC[n] (see Fig. 1b)), which are the monocyclic isomers of linear carbon chains, have also attracted considerable attention in recent years [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] . Note that c-CC [n] (where the carbon atoms are also sp-hybridized) are hypothesized to be the building blocks of fullerenes in the initial stages of growth 21 .…”

“…Among them, c-CC [18] has recently been synthesized 26 , and some of the electronic properties of c-CC [18] have been reported. There are also a few theoretical studies on the electronic properties and applications of c-CC [18] and other cyclic carbon chains 22,[27][28][29][30][31][32][33][34][35][36][37][38] . For example, c-CC [18] has been found to possess electron-acceptor properties, and can be dubbed as the smallest all-carbon electron acceptor 28 .…”

Encapsulation of monocyclic carbon clusters into carbon nanotubes: A continuum modeling approach

“…A very recent study by Li et al 53 probed the structures and stabilities of carbon rings and demonstrated the geometries of carbon rings C n ( n = 10 − 34 ) to be circular. Therefore, in the continuum model, a carbon ring is modeled as a circular ring of radius b possessing uniform distribution of carbon atoms and a CNT is modeled as a cylinder of radius a with a surface of uniformly distributed carbon atoms.…”