Heterocluster-Assembled Crystalline Hydrophobic Complexes with Delayed Fluorescence

Abstract

Metal–organic frameworks (MOFs) with metal─sulfur bonds exhibit unique electrical, redox, and optical properties. However, their development has been hindered by rapid nucleation during crystallization. To address this challenge, amine-based modulators to retard nucleation through competitive coordination with ligands, enabling the synthesis of a series of Cu-S cluster-based MOFs with diverse network topologies: Cu-BDT-hcb (1), Cu-TBT-acs (2), Cu-TBT-pcu (3), Cu-TBT-sql (4), Cu-TBT-dia (5), and Cu-TBT-hcb (6), are utilized. Using donor-acceptor (D-A) ligands (o/p-mercaptobenzoic acid—^o/pMBA), [Sn₄]-based MOFs: Sn-^oDTBA-cds (7) and Sn-^pDTBA-pcu (8), are fabricated. During synthesis, sulfhydryl groups underwent reductive coupling to generate novel dicarboxylate ligands with disulfide (S–S) linkages. Notably, the first bimetallic heterocluster MOF, SnCu-^mMBA-dia (9), incorporating both a metal-oxygen cluster [Sn₄O₂(carboxylate)₄] and a metal-sulfur cluster [Cu₈(thiolate)₈] is developed. This framework, constructed using m-mercaptobenzoic acid (^mMBA) as a D–A bifunctional ligand, exhibits spatially separated HOMO and LUMO, minimizing the singlet–triplet energy gap to promote thermally activated delayed fluorescence (TADF). Compound 9 also demonstrates exceptional hydrolytic stability due to steric shielding by hydrophobic organotin moieties. This work pioneers a modulator-assisted strategy for heterocluster MOF construction, offering a paradigm for designing stable luminescent materials with tailored optoelectronic functionalities.