Conformational Effects on Structure, Electron States, and Raman Scattering Properties of Linear Carbon Chains Terminated by Graphene-Like Pieces

Abstract

Carbon nanowires made of long linear atomic chains have attracted considerable interest due to their potential applications in nanoelectronics. We report a theoretical characterization of assemblies with good prospects for chemical synthesis made of two coronene molecules (graphene-like pieces) bridged by carbon linear chains with distinct sizes and parities. Our calculations are performed within all-electron density functional theory. We examine the effects of two conformations (syn and anti) of the terminal anchor pieces, representing energy minima for these systems, on the properties of the carbon chains. The calculated electronic states reveal that simplified chemical models such as those based on cumulenes or polyynes are not appropriate to describe the linear chains with sp2 terminations. For these types of atomic chains, we find that the electronic ground state of the odd-numbered chains is spin polarized. Vibrational properties of all these chains are studied by calculating Raman scattering and infrared spectra. We show that syn and anti conformations of the graphene-like terminations lead to important effects in the vibrational features of the chains, detectable by the Raman light-scattering depolarization.

Effects of N doping on the electronic properties of a small carbon atomic chain with distinctsp2terminations: A first-principles study

“…32,33 The carbon chain preserves its linear geometry but the corannulene molecule undergoes a significant rotation of about 10 degrees in relation to the coronene plane. Except for this rotational deformation, the structural properties obtained here agree with our previous results performed within all-075417-2 electron DFT for the coronene-C n -coronene structures (n = 3-6), 12 for which the 2 coronene molecules remain in the same plane.…”

“…While in our previous work 12 for a symmetric coronene-C 4 -coronene system the sequence reads 1.420, 1.238, 1.355, 1.238, and 1.420Å. The effect of curvature in one of the terminations (induced by the replacement of coronene for corannulene) brings a negligible change in the bond length closest to this termination.…”

“…The calculated value of the HOMO-LUMO gap is 1.92 eV, which is very similar to that (1.97 eV) obtained for the coronene-C 4 -coronene sytem. 12 By examining the charge density of the frontier molecular orbitals, displayed in Fig. 2(b), the HOMO density is concentrated on the alternating C-C bonds, with less electron density at the bond between the chain and either the corannulene or the coronene terminations [ Fig.…”

“…We consider between 1 and 3 nitrogen atoms occupying different carbon sites in this reference structure. In a previous work 12 we addressed the "pure carbon" coronene-C ncoronene structure (n = 3-6), and we found that its electronic properties depend on its parity. Structures with an even number of C atoms in the chain are singlet (the total spin is 0) and those with an odd number of C atoms in the chain are triplet 12,13 (the total spin is 1).…”

“…[15][16][17][18][19] The model system containing a four carbon atom chain studied in this work has been chosen because such variants of the considered systems, with an even number of carbon atoms in the chain, possess the advantage of exhibiting larger band gaps, in comparison with similar systems containing an odd number of atoms in the chain. 12 To explore a higher structural diversity of nitrogen incorporation sites we have employed 1 coronene molecule and 1 corannulene molecule at the extremities of the chain, instead of symmetric systems consisting of 2 coronene molecules or 2 corannulene molecules.…”