Visible light switching of metallosupramolecular assemblies

30 August 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

A photoswitchable ligand and palladium(II) ions form a dynamic mixture of self-assembled metallosupramolecular structures. The photoswitching ligand is an ortho-fluoroazobenzene with appended pyridyl groups. The E-isomer is combined with palladium(II) salts affords a double-walled triangle with composition [Pd3L6]6+ and a distorted tetrahedron [Pd4L8]8+(1:2 ratio at 298 K). Irradiation with 410 nm light generates a photostationary state with ~80% of the E-isomer of the ligand which results in the selective disassembly of the tetrahedron, the more thermodynamically stable structure, and the formation of the triangle, the kinetic product. The triangle is then slowly transformed back into the tetrahedron over 2 days at 333 K. The Z-isomer of the ligand does not form any well-defined structures and has a thermal half-life of 25 days at 298K. This approach shows how a thermodynamically preferred self-assembled structure can be reversibly pumped to a kinetic trap by small perturbations of the isomer distribution using non-destructive visible light.

Keywords

Self-assembly
photochromic
photoswitchable
azobenzene
supramolecular

Supplementary materials

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Description
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Supplementary Information
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All the supplementary information.
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All the NMR data for this work
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All the 1H, 19F, 13C and 2D NMR data for photoswitches 3 and 4, and the Pd(tty)2+ complex.
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Photoswitching data for 3
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All the UV-vis and NMR data from photoswitching experiments with ligand 3.
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Photoswitching data for 4
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All the UV-vis and NMR data from photoswitching experiments with photoswitch 4.
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Characterisation of self-assembled species
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All NMR (1H, 19F, 13C, 2D and diffusion) and UV-vis absorption data for the self-assembled species [Pd3L6]6+ and [Pd4L8]8+.
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Binding constant measurments
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All binding constant measurements using ITC and competitive binding experiment by 1H NMR.
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Self-assembly with Z-3 and Pd(II)
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1H and 19F NMR data from the reaction of the metastable Z-3 ligand with Pd(II).
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Self-assembly of E-3 with a more soluble Pd(II) complex
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1H NMR data from the self-assembly of ligand E-3 with [Pd(py*)4](BArF)2
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NMR data for Pd(tty)(MeCN) with 3-methylpyridine or ligand E-3.
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1H NMR data for the reaction of [Pd(ttpy)(MeCN)](BF4)2 with 3-methylpyridine or ligand E-3.
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