Design and Syntheses of Electron-Transfer Photochromic Metal–Organic Complexes Using Nonphotochromic Ligands: A Model Compound and the Roles of Its Ligands

Abstract

The model compound [Zn­(HCOO)₂(4,4′-bipy)] (<b>1</b>; 4,4′-bipy = 4,4′-bipyridine) is selected in this work to demonstrate the effectiveness of our previously proposed design strategy for electron-transfer photochromic metal–organic complexes. The electron-transfer photochromic behavior of <b>1</b> has been discovered for the first time. Experimental and theoretical data illustrate that the photochromism of <b>1</b> can be attributed to the electron transfer from formato to 4,4′-bipy and the formation of a radical photoproduct. The electron transfer prefers to occur between formato and 4,4′-bipy, which are combined directly by the Zn­(II) atoms. A high-contrast (up to 8.3 times) photoluminescence switch occurs during the photochromic process. The similarity of photochromic behaviors among <b>1</b> and its analogues as well as viologen compounds has also been found. Photochromic studies of this model compound indicate that new electron-transfer photochromic metal–organic complexes can be largely designed and synthesized by the rational assembly of nonphotochromic electron-donating and electron-accepting ligands