Coupling structural phase transition, thermochromism and magnetic circular dichroism in a Cu(II)-based hybrid perovskite.

Cu(II)-based organic-inorganic hybrid materials have attracted increasing attention due to their structural flexibility and multifunctionality. Herein, we report a layered Cu(II)-based hybrid perovskite, [FAZE]2CuCl4 (FAZE = 3-fluoroazethidine), exhibiting reversible structural phase transition, thermochromic behaviour, and magnetic circular dichroism (MCD). At 326 K, it undergoes a reversible phase transition, accompanied by cation disordering and a reduction in Jahn-Teller distortion. This transition gives rise to an obvious and reversible colour change from green to brown, along with a temperature-dependent redshift in the solid-state UV-vis absorption spectra and a reduction of the optical band gap from 2.33 to 2.25 eV. More importantly, distinct MCD signals are observed under an external magnetic field. This work provides new insights into the design of multifunctional hybrid materials combining thermochromic and magneto-optical functionalities.