Molecular mechanics of glove‐like re(I) metallacycles: Toward light‐activated molecular catchers

Abstract

AbstractTwo novel glove‐shaped rhenium(I)‐based metallacycle complexes, composed of two bidentate ligands α,α′‐bis(benzimidazol‐1‐yl)‐meta(orortho)‐xylene(bbim) and a tetradentate ligand, 2,5‐pyrazinedicarboxylate(pzdc) with two Re(I) metal centers each are developed and reported. The opening and closure motion of the metaxylene‐linked metallacycle complex were studied via variable temperature proton nuclear magnetic resonance spectroscopy experiment, as well as density functional theory calculation. Our results indicate that the motion of the “capping” phenyl moiety in bbim is accompanied by the swing of the two benzimidazol groups. Both complexes show two different emission bands when excited at two different wavelengths, a violation of the Kasha's rule. Theoretical calculation indicate that the lower‐energy transitions are metal–ligand charge transfer bands, arising from electrons localized to one of the two Re(I) centers to the pzdc ligand, while the higher‐energy ones are assigned to a ligand–ligand charge‐transfer excitation from bbim to pzdc. Results from excited‐state optimized structures confirm that the higher‐energy excitation leads to a closure of the molecule with meta‐bbim, a desirable “molecular catcher” behavior. Our findings provide an important insight for a strategy to design a light‐activated molecular catcher for many interesting applications.