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.