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

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 (ΔEst). 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.