Bonding character, electron delocalization, and aromaticity of cyclo[18]carbon (C18) precursors, C18-(CO)n (n = 6, 4, and 2): Focusing on the effect of -CO groups

Abstract

Although the unique cyclo [18]carbon (C 18 ) realized by recent experiments has been greatly concerned, it has so far remained elusive. In contrast, its precursors C 18 -(CO) n (n = 6, 4, and 2), which can be separated stably, are of more practical significance. In this paper, the bonding character, electron delocalization, and aromaticity of the C 18 -(CO) n (n = 6, 4, and 2) with out-of-plane and in-plane dual π systems (π out and π in ) perpendicular to each other are studied by combining quantum chemical calculations and wavefunction analyses. These cyclocarbon oxides exhibit alternating long and short C-C bonds and extensive electron delocalization, and a significant diatropic induced ring current under the action of external magnetic field is therefore observed, which reveals the aromatic characteristic in the molecules. The global electron delocalization and significant influence of the number of intramolecular carbonyl (-CO) on the two sets of π conjugated systems have been focused on, and the essential reason for the distinct difference in the overall aromaticity of the molecules was also clarified. It seems that the substituent -CO groups hinders the electron delocalization of the π in system but has relatively small effect on the π out system, resulting in the molecules with less -CO group showing greater aromaticity.

Photophysical property and optical nonlinearity of cyclo[18]carbon (C18) precursors, C18-(CO)n (n = 2, 4, and 6): Focusing on the effect of carbonyl (-CO) groups

“…For corresponding Cartesian coordinates, please refer to the supplementary material of Ref. [28]. All precursors are observed to be strictly planar, and molecules with n = 2, 4, and 6 belong to C 2v , C 2v , and D 3h point groups, respectively.…”

“…The geometric structures and excitation characteristics of the C 18 -(CO) n (n = 2, 4, and 6) were respectively obtained by DFT and time-dependent DFT (TD-DFT) calculations at ωB97XD [29]/def2-TZVP [30] level in the gas phase. Our recent theoretical work has demonstrated that this computational strategy can reproduce the crystal structure of C 18 -(CO) 6 well, so it is considered to be competent to describe the present systems [28]. The molecular (hyper)polarizabilities were calculated by both analytic derivatives of the system energy [namely, coupled-perturbed Kohn-Sham (CPKS)] and finite field (FF) methods at the ωB97XD/aug-cc-pVTZ(-f,-d) level, where aug-cc-pVTZ(-f,-d) is a reduced version of the aug-cc-pVTZ basis set [31] with the removal of f-type polarization functions of non-hydrogen atoms and d-type polarization functions of hydrogen atoms.…”

“…Although the theoretical studies on various physicochemical properties and behaviors of C 18 ring and its analogues have been quite extensive [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], the research on the precursors C 18 -(CO) n (n = 2, 4, and 6) for manufacturing C 18 has not been fully carried out. As 4 far as we know, only our latest work has systematically studied and comparatively analyzed bonding character, electron delocalization, and aromaticity of relevant systems up to now [28]. The results show that C 18 -(CO) n (n = 2, 4, and 6) possess two perpendicular π-conjugated electron systems, in-plane and out-of-plane π molecular orbitals (MOs), similar to the C 18 ring.…”

Photophysical property and optical nonlinearity of cyclo[18]carbon (C18) precursors, C18-(CO)n (n = 2, 4, and 6): Focusing on the effect of carbonyl (-CO) groups

“…The geometric structures and excitation characteristics of the C 18 -(CO) n (n = 2, 4, and 6) were respectively obtained by DFT and time-dependent DFT (TD-DFT) calculations at ωB97XD [29]/def2-TZVP [30] level in the gas phase. Our recent theoretical work has demonstrated that this computational strategy can reproduce the crystal structure of C 18 -(CO) 6 well, so it is considered to be competent to describe the present systems [28]. The molecular (hyper)polarizabilities were calculated by both analytic derivatives of the system energy [namely, coupled-perturbed Kohn-Sham (CPKS)] and finite field (FF) methods at the ωB97XD/aug-cc-pVTZ(-f,-d) level, where aug-cc-pVTZ(-f,-d) is a reduced version of the aug-cc-pVTZ basis set [31] with the removal of f-type polarization functions of non-hydrogen atoms and d-type polarization functions of hydrogen atoms.…”

Novel dual-motor nanorotator assembled by cyclo[18]carbon and figure-eight carbon hoop

“…In the past two years, various theoretical studies involving the properties, [17][18][19][20][21][22][23][24][25][26][27][28] behaviors, [29][30][31][32][33] and potential applications [34][35][36][37] of C 18 and its analogues and derivatives have been carried out by several research groups. Among these, the theoretical design of supramolecular complex by Jiang et al showed that C 18 can be hosted inside the [11]CPP through intermolecular π-π interaction, [35] emphasizing the potential of C 18 as a building block to construct molecular devices by residing in carbon materials of suitable size and shape.…”