Perfluorocycloparaphenylenes

Abstract

Perfluorinated aromatic compounds, the so-called perfluoroarenes, are widely used in materials science owing to their high electron affinity and characteristic intermolecular interactions. However, methods to synthesize highly strained perfluoroarenes are limited, which greatly limits their structural diversity. Herein, we report the synthesis and isolation of perfluorocycloparaphenylenes (PFCPPs) as a class of ring-shaped perfluoroarenes. Using macrocyclic nickel complexes, we succeeded in synthesizing PF[n]CPPs (n = 10, 12, 14, 16) in one-pot without noble metals. The molecular structures of PF[n]CPPs (n = 10, 12, 14) were determined by X-ray crystallography to confirm their tubular alignment. Photophysical and electrochemical measurements revealed that PF[n]CPPs (n = 10, 12, 14) exhibited wide HOMO-LUMO gaps, high reduction potentials, and strong phosphorescence at low temperature. PFCPPs are not only useful as electron-accepting organic materials but can also be used for accelerating the creation of topologically unique molecular nanocarbon materials.

Fig. 1. Fluorocarbon molecules.

a Structures of fluorofullerenes, perfluororubrene, perfluorocoranullene (top), and perfluorocycloparaphenylenes (PFCPPs) (bottom). b A synthetic scheme of previously reported partially fluorinated CPPs. c The synthetic strategy for PFCPPs (this work).

Fig. 2. Synthesis of PFCPPs.

Reaction conditions: (i) LDA, Ni(dnbpy)Br₂, THF, −78 °C, 30 min; (ii) DDQ, m-xylene, 130 °C, 5 h. LDA = lithium diisopropylamide; dnbpy = 4,4′-di-n-nonyl-2,2′-bipyridyl; DDQ = 2,3-dichloro-5,6-dicyano-p-benzoquinone.

Fig. 3. X-ray crystal structures of PF[n]CPPs (n = 10, 12, 14).

a, b, c Structures of PF[10]CPP (a), PF[12]CPP (b), and PF[14]CPP (c) with thermal ellipsoids at 50% probability. Solvent molecules are omitted for clarity. d, e, f Packing structures of PF[10]CPP (d), PF[12]CPP (e) and PF[14]CPP (f); gray: carbon; green: fluorine. Solvent molecules are omitted for clarity. g The dihedral angles (θ) around the C–C single bonds of PFCPPs and corresponding CPPs^, . Calculations were performed at the B3LYP/6-31G(d) level of theory. Dihedral angles obtained from X-ray crystallography are averaged.

Fig. 4. Photophysical properties of PF[n]CPPs (n = 10, 12, 14).

a UV–Vis absorption spectra of dichloromethane solutions of PFCPPs at room temperature (solid lines), and photoluminescence spectra of PFCPPs in ethanol grass at 77 K upon excitation at 270 nm (dashed lines); blue: PF[10]CPP; red: PF[12]CPP; green: PF[14]CPP. b Cyclic voltammograms of PFCPPs in acetonitrile (supporting electrolyte: [n-Bu₄N][PF₆]; scan rate: 0.1 V s⁻¹). c Frontier molecular orbitals (isovalue: 0.02) and their energies (eV) of [10]CPP and PF[10]CPP calculated by B3LYP/6-31G(d) level of theory. Fc ferrocene.