Synthesis and Properties of Acetylenic Scaffolds Modeling Segments of 6,6,12-Graphyne.

6,6,12-Graphyne is an all-carbon network formally generated by interspersing sp- and sp2-hybridized carbon atoms between the carbon hexagons of graphene. Tetraethynylethene (TEE) is one structural unit that can be identified as bridging the benzene rings in 6,6,12-graphyne. Here we present the synthesis by stepwise Sonogashira couplings of TEE scaffolds that can be considered as small model systems of 6,6,12-graphyne segments. Electrochemical studies of the scaffolds revealed that they are weaker electron acceptors than related, but smaller, radiaannulene oligomers that were previously studied as relevant model systems of other 6,6,12-graphyne segments. The connectivity of the TEE units in these acyclic oligomers plays a role for their acceptor strengths according to experiments and quantum-chemical calculations. Moreover, optical studies reveal redshifted longest-wavelength absorptions as the oligomer length increases, but only to a small degree when moving from dimer to trimer structures. Experimental results were complemented by calculated absorption and redox properties.