Abstract
With the aim of determining the best input geometry for DFT calculations of [60]PCBM, the geometry of 24 chemically possible [60]PCBM conformers were optimised and their electronic energies and average bond strains were determined. A DFT analysis of the relevant dihedral angles provided insights into the dynamical behaviour of the ester group through sterically restricted bond rotations. In addition, the 13C NMR spectra of the six better performing conformers were simulated and compared with an experiment. There is a close correlation between average bond strain, total electronic energy and mean absolute error of the simulated 13C NMR spectra of the ester carbons. The best overall candidate conformer for the input geometry had the C61-C4, C4-C3 and C3-C2 single bonds of the alkyl chain in syn, anti and anti arrangements, respectively, and had the C2-C1 and C1-O single bonds of the ester in syn and anti arrangements, respectively. This contrasts strikingly with most representations of PCBM in the literature, which depict all relevant bonds in anti arrangements.
Highlights
Conformational Analysis of [60]PCBM from DFT Simulations of Electronic Energies, Bond Strain and the 13 C NMR Spectrum: Input
The gauge independent atomic orbitals (GIAO) DFT simulations of the 13 C NMR spectrum employed the ωB97XD method coupled with the cc-pVTZ basis set
One of the methyl hydrogens must be on the mirror plane and the other eight hydrogens of the ester group must exit in mirrored pairs bisecting the mirror plane
Summary
Conformational Analysis of [60]PCBM from DFT Simulations of Electronic Energies, Bond Strain and the 13 C NMR Spectrum: Input. Haina-Carbon Nanostructure Research Center, Yangtze Delta Region Institute of Tsinghua University, Abstract: With the aim of determining the best input geometry for DFT calculations of [60]PCBM, the geometry of 24 chemically possible [60]PCBM conformers were optimised and their electronic energies and average bond strains were determined. The best overall candidate conformer for the input geometry had the C61-C4, C4-C3 and C3-C2 single bonds of the alkyl chain in syn, anti and anti arrangements, respectively, and had the C2-C1 and C1-O single bonds of the ester in syn and anti arrangements, respectively This contrasts strikingly with most representations of PCBM in the literature, which depict all relevant bonds in anti arrangements. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
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