Synthesis of Ligands for MOF and DSSC Applications

Abstract

Metal-Organic Frameworks (MOFs) and Dye-Sensitized Solar Cells (DSSCs) represent promising technologies designed to address sustainability challenges. The properties and characteristics of both rely in large on organic linkers, whose structural and electronic properties dictate much of the overall functionality and performance. In this work, an extended tpy-based linker and two variants of a benzimidazole-based ligands were synthesized and characterized for applications in MOFs and DSSCs respectively. The tpy ligand structure was confirmed by 1H/13C NMR, while the benzimidazole ligands were verified by 1H/13C NMR and MS. The symmetric tpy ligand was obtained through a multi-step process, starting with a Suzuki cross coupling reaction yielding 4-(6-acetylpyridin-3-yl)benzoic acid, followed by a Kröhnke pyridine synthesis to produce the extended tpy diacid in good yield. Owing to its extended conjugated system, the tpy diacid was complexed with ruthenium and iron to investigate their photophysical properties, notably fluorescence spectroscopy. The extended diacid functional groups provide symmetrical binding sites, thus supporting the potential construction of three-dimensional MOFs with photocatalytic activity attributed to the tpy unit. In parallel, benzimidazole-based ligands were designed to be complexes with Cu(I) and Cu(II) metal centers for DSSC applications. their syntheses followed a three-step process, highlighted by a final Weidenhagen benzimidazole reaction to yield the pyridyl modified benzimidazole products. Notably, The alkyl substitution at the 4-position of the benzimidazole ring enforces a distinctive tetrahedral geometry with Cu(I), allowing for the synthesis of highly stable Cu(I)-(ligand)2 complexes. These new Cu(I)/Cu(II) complexes show high potential when incorporated in DSSCs and generating high photo-voltages.