ABSTRACT
A gold(i)-diphosphine simultaneously exhibits reversible mechanochromism and mechanochromic luminescence. The mechanical grinding can trigger a transformation from a neutral mononuclear structure exhibiting white colour and blue photoluminescence to an ionic dinuclear structure with intramolecular aurophilic interactions exhibiting yellow colour and red emission.
ABSTRACT
A series of [Au2 (nixantphos)2](X)2 (nixantphos=4,6-bis(diphenylphosphino)-phenoxazine; X=NO3, 1; CF3 COO, 2; CF3 SO3, 3; [Au(CN)2], 4; and BF4, 5) complexes that exhibit intriguing anion-switchable and stimuli-responsive luminescent photophysical properties have been synthesized and characterized. Depending on their anions, these complexes display yellow (3), orange (4 and 5), and red (1 and 2) emission colors. They exhibit reversible thermo-, mechano-, and vapochromic luminescence changes readily perceivable by the naked eye. Single-crystal X-ray studies show that the [Au2 (nixantphos)2](2+) cations with short intramolecular Auâ â â Au interactions are involved as donors in an infinite N-Hâ â â X (X=O and N) hydrogen-bonded chain formation with CF3 COO(-) (2 C) and aurophilically linked [Au(CN)2](-) counterions (4 C). Both crystals show thermochromic luminescence; their room temperature red (2 C) and orange (4 C) emission turns into yellow upon cooling to 77â K. They also exhibit reversible mechanochromic luminescence by changing their emission color from red to dark (2 C), and orange to red (4 C). Compounds 1-5 also display reversible mechanochromic luminescence, altering their emission colors between orange (1) or red (2) to dark, as well as between yellow (3) or orange (4 and 5) to red. Detailed photophysical investigations and correlation with solid-state structural data established the significant role of NHâ â â X interactions in the stimuli-responsive luminescent behavior.