Decorating Metal Nitrate with Coplanar Bipyridine Moiety: a Simple and General Method for Fabricating Photochromic Complexes

As a significant class of photochromic materials, crystalline hybrid photochromic materials (CHPMs) have attracted widespread attention of researchers because of their possibilities for generating other photoresponsive properties and advantages in understanding the underlying relationship between structure and photoresponsive performance. The predesign of suitable ligands plays a major role in generating desirable CHPMs. Hitherto, most CHPMs have been built from photodeformable or photoresponsive tectons. However, the synthesis of these ligands is usually time-consuming and expensive, and this greatly restricts their large-scale preparation and practical application. Therefore, it is necessary to explore new families of CHPMs besides the existing CHPMs. Herein, a simple and general method for constructing CHPMs by decorating metal nitrate with a coplanar bipyridine moiety, namely 1,10-phenanthroline (phen), is reported. The resulting products exhibit photocoloration in response to Xe-lamp irradiation. The electron transfer (ET) from the coplanar NO3- species (as π-electron donors, π-EDs) to coplanar phen moieties (as π-electron acceptors, π-EAs) is responsible for the resulting photochromism. The influence of the coordination environment and central metal ion on the photochromism was also studied. This work demonstrates that the introduction of coplanar organic tectons as π-EAs to metal nitrates as π-EDs with the collaboration of ET and coordination-assembly strategies is a simple and general method to manufacture CHPMs.