Molecular Design of a Metal-Nitrosyl Ferroelectric with Reversible Photoisomerization
Wei‐Jian Xu, Mao-Fan Li, Ana R. García, Konstantin Romanyuk, J. M. G. Martinho, Pavel Zelenovskii, Alexander Tselev, Luís M.P. Veríssimo, Wei‐Xiong Zhang, Xiao‐Ming Chen, Andréi L. Kholkin, João Rocha
Abstract
High Resolution Image Download MS PowerPoint Slide The development of photo-responsive ferroelectrics whose polarization may be remotely controlled by optical means is of fundamental importance for basic research and technological applications. Herein, we report the design and synthesis of a new metal-nitrosyl ferroelectric crystal (DMA)(PIP)[Fe(CN) 5 (NO)] ( 1 ) (DMA = dimethylammonium, PIP = piperidinium) with potential phototunable polarization via a dual-organic-cation molecular design strategy. Compared to the parent non-ferroelectric (MA) 2 [Fe(CN) 5 (NO)] (MA = methylammonium) material with a phase transition at 207 K, the introduction of larger dual organic cations both lowers the crystal symmetry affording robust ferroelectricity and increases the energy barrier of molecular motions, endowing 1 with a large polarization of up to 7.6 μC cm –2 and a high Curie temperature ( T c ) of 316 K. Infrared spectroscopy shows that the reversible photoisomerization of the nitrosyl ligand is accomplished by light irradiation. Specifically, the ground state with the N-bound nitrosyl ligand conformation can be reversibly switched to both the metastable state I (MSI) with isonitrosyl conformation and the metastable state II (MSII) with side-on nitrosyl conformation. Quantum chemistry calculations suggest that the photoisomerization significantly changes the dipole moment of the [Fe(CN) 5 (NO)] 2– anion, thus leading to three ferroelectric states with different values of macroscopic polarization. Such optical accessibility and controllability of different ferroelectric states via photoinduced nitrosyl linkage isomerization open up a new and attractive route to optically controllable macroscopic polarization.