Boron Complexes of Tridentate Acyl Pyridylhydrazones

A series of boron complexes of tridentate acyl pyridylhydrazones were prepared. Their facile synthesis relies on arylboronic acids for boron incorporation, enabling significant structural diversity, dual-state emission, and reversible electrochemical reductions. Donor-acceptor architectures, constructed by leveraging triphenylamine and carbazole-functionalized arylboronic acids, result in aggregation-induced emission enhancement.

Abstract

Since the development of the chemistry and applications of boron dipyrromethene dyes (BODIPYs), numerous other platforms based on boron complexes of N-donor ligands have emerged as molecular optoelectronic materials. By tailoring the structure of the ligand bound to boron, the optical and electronic properties of a compound can be precisely tuned for unique properties, such as aggregation-induced emission (AIE) in the case of boron difluoride hydrazones (BODIHYs). We examine the impact of modifying the typical bidentate hydrazone ligand structure used to prepare BODIHYs to enable a tridentate coordination mode to produce boron complexes of tridentate acyl pyridylhydrazones. This change allows for the use of arylboronic acids as sources of boron and facilitates the inclusion of complex organic components at the boron centre, including the formation of dye-dye conjugates. The synthesized compounds exhibit distinct optical and electronic properties when compared to BODIHYs, such as reversible electrochemical reduction and up to a >300 nm pseudo-Stokes shift in the solid state, all of which were supported by density functional theory calculations.

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