Tetraethynylethenes: Versatile Carbon-Rich Building Blocks for Two-Dimensional Acetylenic Scaffolding

摘要

Derivatives of tetraethynylethene (TEE, 3,4-diethynyl-hex-3-ene-l,5-diyne) constitute a versatile "molecular construction kit" for acetylenic molecular scaffolding. TEEs have been introduced into multinanometer-sized functional molecular and polymeric materials with stable, extended carbon cores that exhibit unusual electronic and optical properties. In addition, the planar TEE carbon frame is a basic repeat unit for the construction of two-dimensional crystalline all-carbon networks. Starting from cis-bis-deprotected TEEs, annulenes were prepared as macrocyclic precursors to such networks. The challenges encountered in the formation of extended regular carbon networks by oxidative acetylenic coupling are discussed, and techniques from supramolecular chemistry are proposed to overcome the difficulties that prevented their preparation so far. One approach consists in the self-assembly of metal-acetylenic networks under thermodynamic control and error checking, followed by reductive elimination of the metal centers to the all-carbon net. Expanded radialenes represent another class of stable, extended carbon-rich compounds which were prepared for the first time starting from TEE precursors. 7ra/M-bis-deprotected TEEs provided access to rod-like oligomers and polymers with the novel polytriacetylene (PTA) backbone. The redox-properties of these remarkably stable materials are discussed. Tetrakis(phenylethynyl)ethene was shown to form highly ordered charge-transfer complexes with ^-acceptors in the solid state and in solution. By attaching p-donor and p-acceptor substituted phenyl rings to TEEs, novel NLO materials were obtained. It was shown for a large class of TEEs that donor/acceptor substitutions and fully two-dimensional conjugation strongly enhance the third-order nonlinear optical properties. The relevance of the results obtained from studies of extended unsaturated carbon-rich materials for carbon allotropy in general is discussed.