Light-Induced Tunable Ferroelectric Polarization in Dipole-Embedded Metal-Organic Framework

Reversible regulation of ferroelectric polarization possesses great potentials recently in bionic neural networks. Photoinduced cis-trans isomers have changeable dipole moments, but they cannot be directed to some specific orientation. Here, we construct a host-guest composite structure which consists of a porous ferroelectric metal (Ni)-organic framework [Ni(DPA)₂] as host and photoisomer, azobenzene (AZB), as guest molecules. When AZB molecules are embedded in the nanopores of Ni(DPA)₂ in the form of a single molecule, polarization strength tunable regulation is realized after ultraviolet irradiation of 365 and 405 nm via cis-trans isomerism transformation of AZB. An intrinsic built-in field originating from the distorted {NiN₂O₄} octahedra in Ni(DPA)₂ directs the dipole moments of AZB to the applied electric field. As a result, the overlapped ferroelectric polarization strength changes with content of cis-AZB after ultraviolet and visible irradiation. Such a connection of ferroelectric Ni(DPA)₂ structure with cis-trans isomers provides an important strategy for regulating the ferroelectric polarization strength.