Photochromism of supramolecular assemblies based on benzenecarboxylate donors and viologen acceptors

Abstract

Four different host–guest supramolecular assemblies of 1,2,4,5-benzenetetracarboxylic acid (H₄BTEC) and viologens have been prepared, [(PV)_0.5(H₄BTEC)_0.5]·NO₃ (1), [(PV)(H₂BTEC)]·H₂O (2), (H₃O)(PV)_0.5(H₂BTEC) (3), and [(AV)_0.5(H₄BTEC)_0.5(H₂BTEC)_0.5]·H₂O (4), (PV²⁺ = 1,1′-bis(propyl)-4,4′-bipyridinium dication; AV²⁺ = 1,1′-bis(amyl)-4,4′-bipyridinium dication). The electron-donating acid moieties acting as the host form supramolecular assemblies with electron-deficient viologens as the guest, which are connected by non-covalent interactions to make the donor–acceptor (D–A) system. Compounds 2–4 all exhibit electron-transfer (ET) photochromic behaviors, while compound 1 has no observed photochromism. The results show that the balance between intermolecular electron transfer and consequent photochromism is due to the rational modulation of electron acceptors and donors.