C ₆ H ₇ NCl·X (X = Cl, Br): Outstanding Multifunctional Nonlinear Optical and Birefringent Crystals Enabled by Incorporation of π‐Conjugated Moieties

ABSTRACT Organic‐inorganic hybrid nonlinear optical (NLO) and birefringent materials, especially those with the introduction of π‐conjugated organic optoelectronic cations, have attracted considerable attention due to their excellent performance and promising applications. Herein, two novel 0D noncentrosymmetric hybrid materials, C 6 H 7 NCl·Cl and C 6 H 7 NCl·Br, were successfully synthesized by combination of π‐conjugated 2‐chloroanilinium ([C 6 H 7 NCl] + ) cations and strong electronegative halide anions (X − , X = Cl, Br). Notably, both compounds exhibit significant second‐harmonic generation (SHG) intensities of 0.86 and 1.43 × KDP, mainly attributed to the hydrogen‐bonding interactions and organic π‐conjugated cations. Moreover, short UV cutoff edges of 273 and 276 nm, with large optical band gaps of 4.009 and 3.955 eV were determined for C 6 H 7 NCl·Cl and C 6 H 7 NCl·Br, respectively. Furthermore, first‐principles calculations were conducted to investigate the structure‐property relationship. Significantly, large birefringence values of 0.267 and 0.220 @ 546 nm were observed for C 6 H 7 NCl·Cl and C 6 H 7 NCl·Br, respectively, which originate from the strong anisotropic conjugated π‐electron distribution of their organic groups. This work not only presents two novel UV SHG and birefringent crystals, but also offers a valuable reference for designing and synthesizing of new high‐performance nonlinear optical (NLO) hybrid and birefringent crystals containing planar π‐conjugated organic units.