Photoluminescent and ferroelectric properties of a chiral rhenium(I) complex based on the chiral (−)-4,5-pinene-2,2′-bipyridine ligand

A rhenium(I) complex ReLR,R(CO)3Cl (1) based on a chiral ligand, LR,R = (−)-4,5-pinene-2,2′-bipyridine [(6R)-5,6,7,8-tetrohedro-7,7-dimethyl-3-(2-pyridinyl)-6,8-methanoisoquinoline], was synthesized and characterized. The emission spectrum of 1 shows efficient dπ(Re) → π* (diimine) (MLCT) phosphorescence with a photoluminescence quantum efficiency of 0.035. The excited state lifetimes of Re(I) complex, measured in CH2Cl2 solution (1.82 μs) and solid state (2.15 μs) at room temperature, support the hypothesis of the MLCT character of the emitting state. Single crystal X-ray diffraction analyses show that complex 1 crystallizes in the chiral space group P21 of monoclinic system. The P–E hysteresis loop indicates its obvious ferroelectricity with the remnant polarization (Pr) value of 0.17 μC/cm2 at an applied field of 4.8 kV/cm. To the best of our knowledge, complex 1 represents the first rhenium-based complex reported with ferroelectricity.