Synthesis, Characterization, and Photophysics of Self-Assembled Mn(II)-MOF with Naphthalene Chromophore

The unique and highly organized three-dimensional structure of metal–organic frameworks (MOFs) formed by self-assembled organic chromophores with metal ions emerges as next-generation luminophores for optoelectronic devices. Herein, for the first time, we have investigated the photophysics of self-assembled Mn(II)-MOF microstructures, consisting 2,6-naphthalenedicarboxylic acid (NDC), as a blue luminophore. The crystalline octahedral structure of Mn-MOF with a rigid framework of NDC units exhibits solvent-driven charge transfer dynamics, inducing either chromophore-localized luminescence or ligand-to-metal charge transfer luminescence in solution phase, while only the ligand-centered luminescence is observed in thin films. The excited-state emission lifetime decay experiments of Mn-MOF reveal the exciton behavior of the ligand, which corresponds to chromophore’s S 1 →S 0 emission within the MOF framework. The excited-state fluorescence lifetime decay profile of NDC within the MOF structure exhibits a shorter exciton lifetime, which is 5.58 ns, compared to the excited-state emissive lifetime of the linker alone, evidencing the dependency of the chromophore emission by the topology of the Mn-MOF three-dimensional structure. The rigidity and interpenetrated arrangement of NDC chromophores may contribute to the shorter excited-state emissive lifetime, evidencing that the ligand arrangement plays a key role in the photophysical properties of Mn-MOFs.