Probing Colossal Carbon Rings

Abstract

Carbon aggregates containing between 10 and 30 atoms preferentially arrange themselves as planar rings. To learn more about this exotic allotrope of carbon, electronic spectra are measured for even cyclo[n]carbon radical cations ( normalC 14 + – normalC 36 + ) using two-color photodissociation action spectroscopy. To eliminate spectral contributions from other isomers, the target cyclo[n]carbon radical cations are isomer-selected using a drift tube ion mobility spectrometer prior to spectroscopic interrogation. The electronic spectra exhibit sharp transitions spanning the visible and near-infrared spectral regions with the main absorption band shifting progressively to longer wavelength by ≈100 nm for every additional two carbon atoms. This behavior is rationalized with a Hückel theory model describing the energies of the in-plane and out-of-plane π orbitals. Photoexcitation of smaller carbon rings leads preferentially to neutral C3 and C5 loss, whereas rings larger than normalC 24 + tend to also decompose into two smaller rings, which, when possible, have aromatic stability. Generally, the observed charged photofragments correspond to low energy fragment pairs, as predicted by density functional theory calculations (CAM-B3LYP-D3(BJ)/cc-pVDZ). Using action spectroscopy it is confirmed that normalC 14 + and normalC 18 + photofragments from normalC 28 + rings have cyclic structures.

On-Surface Synthesis of a Doubly Anti-Aromatic Carbon Allotrope: Cyclo[16]carbon

“…S8, S9). Previously, gas-phase C16 has been formed from a molecular precursor 37,38 , and studied in its anionic [38][39][40] and cationic 18,41 forms, but this is the first time C16 has been generated in a condensed phase or structurally characterised.…”

“…detected in the gas-phase 17,18 , and two examples (C6 and C8) have been trapped in solid argon and characterised by infrared spectroscopy 19,20 . Cyclo [10]carbon, cyclo [14]carbon and cyclo [18]carbon have been definitively characterised by scanning probe microscopy of individual molecules on NaCl surfaces at low temperature 9,10,21 . AFM images revealed cumulenic structures for C10 and C14 (ref.…”

On-Surface Synthesis of a Doubly Anti-Aromatic Carbon Allotrope: Cyclo[16]carbon

“…They are intermediates in the formation of fullerenes (13), and they constitute possible building blocks for other carbon allotropes such as graphyne (14). Many cyclocarbons (N = 6-40) have been detected in the gas-phase (15,16), and two examples (C6 and C8) have been trapped in solid argon and characterized by infrared spectroscopy (17,18). The only cyclocarbons yet to have been synthesized in a condensed phase or definitively characterized are cyclo [10]carbon and cyclo [18]carbon.…”

“…S8, S9). Previously, gas-phase C16 has been formed from a molecular precursor (35,36), and studied in its anionic (36)(37)(38) and cationic (16,39) forms, but this is the first time C16 has been generated in a condensed phase. The yield for the on-surface synthesis of C16 was about 30%; in unsuccessful attempts, the ring opened to form linear polyynic chains (see fig.…”

Cyclo[n]carbons and catenanes from different perspectives: disentangling the molecular thread

“…All-carbon chemistry and physics is a fast-growing field with numerous potential applications in materials science, [1][2][3][4][5][6] molecular electronics, [7][8][9][10] catalysis, 11-13 spectroscopy [14][15][16] and combustion. Carbon clusters are in the focus of astrochemistry/astrophysics, and chemistry of fullerenes, carbon-nanotubes and conducting polymers.…”