Chiral Metal–Organic Frameworks with Multiple and Highly Anisotropic Nonlinear Optical Effects

Abstract

The design and construction of photonic materials with multiple and anisotropic nonlinear optical (NLO) behaviors for all-photonic device applications is an attractive but challenging task. Herein, we present a generalizable polarity–chirality synergy strategy that employs donor−π–acceptor (D-π-A)-type organic molecules as polar linkers for assembling chiral metal–organic frameworks (MOFs), in which polarity governs the NLO properties while chirality enables symmetry breaking. Through a chiral induction method, a pair of novel chiral MOFs, LaTCA-L and LaTCA-D, were synthesized by using 4,4″,4‴-tricarboxyltriphenylamine (H3TCA) as the ligand and lanthanum ions as the metal nodes. The LaTCA-L and LaTCA-D crystals simultaneously exhibit significant photoluminescence and second-order and third-order NLO effects with a second-harmonic generation (SHG) intensity of up to 11 times that of the classic KH2PO4 (KDP) crystal. In addition, the LaTCA-L crystal shows obvious linear polarization-dependent SHG, third-harmonic generation (THG), and two-photon-excited photoluminescence (2PEL) with a high degree of polarization (DOP) up to 99.0% under excitation wavelengths ranging from 900 to 1800 nm. In particular, the MOF LaTCA-L exhibits gSHG-CD values of 0.79 and 0.86 at 1030 nm, with identical circular-polarization-dependent SHG trends confirmed at 1064 and 1310 nm. Moreover, this construction strategy can be easily expanded to other D-π-A type organic ligands such as 1,3,5-tris(4-carboxyphenyl)benzene acid (H3BTB), thus opening a pathway toward designing multifunctional chiral MOFs with promising potential for photonic applications.