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.