Photoluminescence and Nonlinear Optical Properties of Two Terpyridine-Based Hybrid Zn/Cd Halides

Hybrid metal halides (HMHs) with low-dimensional structures have attracted increasing attention due to their striking optical properties. Herein, two new zero-dimensional HMHs have been fabricated by CdCl₂/ZnCl₂ and 4'-(4-pyridyl-phenyl)-2,2':6',2″-terpyridine (Tpy), including (TpyH₃)[CdCl₄][Cl] (Tpy-Cd) and (TpyH₃)[ZnCl₄][Cl] (Tpy-Zn). Their structures are consisted of a [TpyH₃]³⁺ organic cation, an inorganic [ZnCl₄] or [CdCl₄] tetrahedron, and one isolated Cl^- anion. Tpy-Cd crystallizes to a noncentrosymmetric structure and possesses a moderate second harmonic response of 0.72 × KH₂PO₄, while Tpy-Zn features a centrosymmetric space group. Though Tpy-Cd and Tpy-Zn crystallize into space groups of completely different symmetry due to distinct connection mode and molecular distortion, they display quite similar photoluminescence of bright green light emission under ultraviolet excitation, nearly identical in Stokes shift, photoluminescence quantum yield, decay lifetime, and energy. The photoluminescence quantum yields of green light emission were measured to be nearly 25%, outperforming most of the Cd/Zn low-dimensional HMHs.