Rational Combination of π‐Conjugated and Non‐π‐Conjugated Groups Achieving Strong Nonlinear Optical Response, Large Optical Anisotropy, and UV Light‐Switchable Fluorescence

Abstract Combining π‐conjugated and non‐π‐conjugated groups is an important strategy for synthesizing new nonlinear optical (NLO) crystals. However, the second harmonic generation (SHG) response and optical anisotropy can be limited by improper spatial alignment of these functional groups in the crystal structure. In this work, it is revealed that non‐π‐conjugated [NH 2 SO 3 ] group acts as both hydrogen bond donor and acceptor, effectively regulating the 2D planar structure formed by π‐conjugated [C 4 N 3 H 6 ] groups. The resulting organic–inorganic hybrid crystal C 4 N 3 H 6 SO 3 NH 2 exhibits a strong SHG response (2.5 × KDP), large optical anisotropy (0.233@546 nm), and blue‐violet and green fluorescence near 360 and 520 nm, respectively. This work expands the methodology for creating new NLO crystals through organic–inorganic hybridization, while also showcasing the potential of C 4 N 3 H 6 SO 3 NH 2 as a multifunctional optical material.