Concomitant Photoresponsive Chiroptics and Magnetism in Metal-Organic Frameworks at Room Temperature
Bin Xia, Qian Gao, Zhenpeng Hu, Qing‐Lun Wang, Xuewei Cao, Wei Li, You Song, Xian‐He Bu
Abstract
Stimulus-responsive metal-organic frameworks (MOFs) can be used for designing smart materials. Herein, we report a family of rationally designed MOFs which exhibit photoresponsive chiroptical and magnetic properties at room temperature. In this design, two specific nonphotochromic ligands are selected to construct enantiomeric MOFs, {Cu 2 (L-mal) 2 (bpy) 2 (H 2 O)·3H 2 O} n (1) and {Cu 2 (D-mal) 2 (bpy) 2 (H 2 O)·3H 2 O} n (2) ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mtext>mal</mml:mtext> <mml:mo>=</mml:mo> <mml:mtext>malate</mml:mtext> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mtext>bpy</mml:mtext> <mml:mo>=</mml:mo> <mml:mn>4</mml:mn> <mml:mo>,</mml:mo> <mml:msup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mtext>’</mml:mtext> </mml:mrow> </mml:msup> <mml:mo>−</mml:mo> <mml:mtext>bipyridine</mml:mtext> </mml:math> ), which can alter their color, magnetism, and chiroptics concurrently in response to light. Upon UV or visible light irradiation, long-lived bpy − radicals are generated via photoinduced electron transfer (PET) from oxygen atoms of carboxylates and hydroxyl of malates to bpy ligands, giving rise to a 23.7% increase of magnetic susceptibility at room temperature. The participation of the chromophores (-OH and -COO − ) bound with the chiral carbon during the electron transfer process results in a small dipolar transition; thus, the Cotton effects of the enantiomers are weakened along with a photoinduced color change. This work demonstrates that the simultaneous responses of chirality, optics, and magnetism can be achieved in a single compound at room temperature and may open up a new pathway for designing chiral stimuli-responsive materials.