Unconventional Heterobidentate Coordination of 4‐Hydroxypyridine Leading to Remarkably Strong Second‐Harmonic Generation in Zn(C5H4NO)2

Herein, we report an unconventional heterobidentate coordination mode of conventional 4‐hydroxypyridine ligand in a novel compound Zn(C5H4NO)2. The strong heterobidentate coordination interactions between Zn2+ and 4‐hydroxypyridine ligands promote a uniform alignment of the polarization of each [ZnO2N2] tetrahedral building unit, resulting in remarkably strong second‐harmonic generation (SHG) with an intensity that is the largest among all UV‐transparent Zn‐containing metal‐organic compounds, reaching 13.6 × KDP. Moreover, Zn(C5H4NO)2 processes a suitable optical bandgap of 4.40 eV, high thermal stability up to 300 °C, excellent air stability, and strong water resistance, demonstrating great application potential. Additionally, Zn(C5H4NO)2 exhibits photoluminescence with a significantly enhanced lifetime of 558 ms, accompanied by a rare blue afterglow visible to the naked eye, lasting up to 5 s.