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Highly Stable Supramolecular Donor-Acceptor Complexes Involving (Z)-, (E)-di(3-pyridyl)ethylene Derivatives as Weak

Artem I Vedernikov¹, Valeriy V Volchkov², Mikhail N Khimich²

¹NRC "Kurchatov Institute", Kurchatov Complex of Crystallography and Photonics, Photochemistry Center, 119421 Moscow, Russia.

Molecules (Basel, Switzerland)

|October 16, 2025

Abstract

None:

The Z-isomer of N,N'-diammoniopropyl derivative of di(3-pyridyl)ethylene was synthesized. The structure and stability of complexes between this non-planar weak acceptor (A, (Z)-2) and a planar strong donor, the E-isomer of bis(18-crown-6)stilbene (D, (E)-1), were studied using X-ray diffraction, ¹H NMR spectroscopy, and optical spectroscopy, including ¹H NMR and spectrofluorimetric titrations. In MeCN, the components form a very stable pseudocyclic bimolecular complex (logK_D·A = 8.48) due to homoditopic coordination of the ammonium groups of the acceptor to the crown moieties of the donor through numerous hydrogen bonds. Intrasupramolecular photo-driven electron transfer (ET) in the isomeric complexes of (E)-1 with (E)- and (Z)-2 was studied using steady-state absorption and fluorescence spectroscopy with time-resolved pulse absorption spectroscopy. It was found that back ET is approximately two times faster in complex (E)-1·(Z)-2 than in closely related (E)-1·(E)-2. Meanwhile, it is ~67 times slower in complex (E)-1·(E)-2 than in the isomeric complex based on N,N'-diammoniopropyl derivative of (E)-di(4-pyridyl)ethylene. Quantum chemical (DFT, TD-DFT) calculations suggest the actual photorelaxation pathway for the complexes under study.

Keywords:

NMR spectroscopy TD-DFT calculations X-ray diffraction bis(crown)stilbene dipyridylethylenes intrasupramolecular photo-driven electron transfer supramolecular complexes time-resolved absorption spectroscopy

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