Tetra(2,3-thienylene) is a thiophene-fused [8]annulene capable of undergoing redox-induced dimensional changes. The feasibility of efficiently translating this intrinsic function into a single polymeric electromechanical actuator is investigated by both experiment and density functional theory (B3LYP 6-31G[d,p]). A study of tetra(2,3-thienylene) and its homodimer reveal that redox-induced conformational change is conserved upon dimerization, a result that implicates similar behavior in the corresponding polymer. Theoretical predictions yield a maximum redox-induced dimensional change of 5.92% per repeat unit for the homodimer. Cyclic voltammetry reveals complete reversibility for the corresponding redox cycle. The latter two facts establish tetra(2,3-thienylene) as a suitable building block for single-molecule electromechanical actuators.

High-content Dewar benzene polymers and sterically congested [n]-ladderanes have been synthesized from [4p s +2p s ] cyclobutadienemetal complex cycloaddition chemistry. In the former case, tetramethylcyclobutadiene-AlCl 3 is reacted with an acetylene-containing precursor polymer to yield > 95% Dewar benzene incorporation. In the latter case, [n]-ladderanes containing up to thirteen rings are prepared via a one-pot procedure from 2-butyne.

Photochemical cyclization of compound 1, a homoenediyne (-CCC=CCH2CC-) bearing two ethynylanthracene chromophores, yields two isomeric dihydrocyclopent[a]indene ring systems, spiro-fused to the 9-position of a 9,10-dihydroanthracene moiety. Evidence of a photochemically initiated diradical cyclization pathway is proposed on the basis of (i) hydrogen abstraction from reaction with 1,4-cyclohexadiene (1,4-CHD) and (ii) the observation of 1,4-addition of benzene (solvent). The reaction was further analyzed by a complete density functional theory (DFT) study, using an unrestricted approach (UBLYP) with a 6-31G* basis set for the open-shell triplet states of the reactants, products, and diradical intermediates to model the photochemical nature of observed transformation. A mechanism detailing the observed cyclization/addition reaction is proposed.