Molecular Engineering of Ionic Metal‐Organic Frameworks via Ligand Conjugation Modulation for Tailored Phosphorescence and Multilevel Encryption

Abstract The rational design of metal‐organic frameworks (MOFs) with tunable phosphorescence remains challenging due to limited understanding of ligand conjugation effects on excited‐state dynamics. Herein, two isomorphic ionic MOFs (IMOF‐DMF and IMOF‐DEF) are constructed via in situ decarbonylation of DMF/DEF, leveraging guest‐ion size to regulate ligand conjugation through modulation of pyridine ring dihedral angles. IMOF‐DEF exhibits superior room‐temperature phosphorescence (RTP) and temperature‐dependent behavior. Mechanistic studies reveal that reduced conjugation enhances intersystem crossing (ISC) by strengthening spin‐orbit coupling while minimizing the singlet‐triplet energy gap (ΔE st ). Furthermore, a dual‐parameter anti‐counterfeiting platform and flexible PVA hydrogel films enable advanced information encryption through temperature/time‐resolved signals and triple‐state lifetime encoding. This work establishes ligand conjugation engineering as a key strategy for tailoring MOF photophysics, linking molecular design to optoelectronic applications and security technologies.