Photoswitching chiroptical response in camphorate-based chiral metal–organic frameworks

Abstract

Photoswitchable chiral materials are highly sought for various applications, including sensing, nonlinear optics, and liquid-crystalline devices. However, the origin and control of switching have not been well studied. Here, we report two chiral naphthalene diimide (NDI)-based Metal Organic Framework (MOF) materials, [Zn₄(cam)₄(DPNDI)₂]·3DMF (Zn-MOF) (cam²⁻ = camphorate, DPNDI = N,N′-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide) and [Cd₄(cam)₄(DPNDI)₄]·3EtOH·5DMF (Cd-MOF) that undergo a photoinduced reduction of the NDI cores. Delocalisation of the generated mixed-valence state in Cd-MOF stabilises the radical state and alters its response in comparison to Zn-MOF. The photoinduced reduction reveals a reversible change in the sign of the circular dichroism spectrum of Cd-MOF. These materials show promise in understanding and controlling chiroptical materials for next-generation devices.