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.