β,β-directly linked porphyrin rings: synthesis, photophysical properties, and fullerene binding

DOI: 10.1021/jacs.3c03549

Authors: Qiang Chen (University of Oxford) , Amber L. Thompson (University of Oxford) , Kirsten E. Christensen (University of Oxford) , Peter N. Horton (University of Southampton) , Simon J. Coles (University of Southampton) , Harry L. Anderson (University of Oxford)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society

State: Published (Approved)
Published: May 2023
Diamond Proposal Number(s): 20876

Abstract: Cyclic porphyrin oligomers have been studied as models for photosynthetic light-harvesting antenna complexes and as potential receptors for supramolecular chemistry. Here, we report the synthesis of unprecedented β,β-directly linked cyclic zinc porphyrin oligomers, the trimer (CP3) and tetramer (CP4), by Yamamoto coupling of a 2,3-dibromoporphyrin precursor. Their three-dimensional structures were confirmed by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and single-crystal X-ray diffraction analyses. The minimum-energy geometries of CP3 and CP4 have propeller and saddle shapes, respectively, as calculated using density functional theory. Their different geometries result in distinct photophysical and electrochemical properties. The smaller dihedral angles between the porphyrin units in CP3, compared with CP4, result in stronger π-conjugation, splitting the ultraviolet–vis absorption bands and shifting them to longer wavelengths. Analysis of the crystallographic bond lengths indicates that the central benzene ring of the CP3 is partially aromatic [harmonic oscillator model of aromaticity (HOMA) 0.52], whereas the central cyclooctatetraene ring of the CP4 is non-aromatic (HOMA –0.02). The saddle-shaped structure of CP4 makes it a ditopic receptor for fullerenes, with affinity constants of (1.1 ± 0.4) × 105 M–1 for C70 and (2.2 ± 0.1) × 104 M–1 for C60, respectively, in toluene solution at 298 K. The formation of a 1:2 complex with C60 is confirmed by NMR titration and single-crystal X-ray diffraction.

Subject Areas: Chemistry


Instruments: I19-Small Molecule Single Crystal Diffraction

Added On: 21/05/2023 16:21

Documents:
jacs.3c03549.pdf

Discipline Tags:

Physical Chemistry Chemistry Chemical Engineering Engineering & Technology Organic Chemistry

Technical Tags:

Diffraction Single Crystal X-ray Diffraction (SXRD)