Electron transfer photochromism of solid-state supramolecules constructed by cucurbit[n]uril (n = 5–8) and 1-(4-carboxybenzyl)-4-[2-(4-pyridyl)-vinyl]-pyridinium chloride

Abstract

Incorporation of the potential photochromic compound 1-(4-carboxybenzyl)-4-[2-(4-pyridyl)-vinyl]-pyridinium chloride (guest 1⁺·Cl⁻) into the macrocyclic hosts cucurbit[n]uril (n = 5–8, Q[n]) generated a new kind of photochromic material. NMR and UV spectra confirm that the guest 1⁺ displays different binding models with the Q[n]s, which depends on the amount of the guest 1⁺ and the cavity size of the hosts. Photochromic properties of the complexes of 1⁺·Cl⁻ with Q[n]s were investigated by solid-state UV-vis diffuse-reflectance and electron-spin resonance (ESR) spectroscopy, which indicate that the photochromic behaviors are caused by the generation of free radical 1˙ via the electron transfer from the hosts to the guest. Ab initio calculations were also carried out to discuss the effects of the Q[n] on photochromic behaviors.