ELECTRONIC CHARACTERISTICS OF ARYLATED TETRAETHYNYLETHENES - A COOPERATIVE COMPUTATIONAL AND ELECTROCHEMICAL INVESTIGATION

A systematic analysis of a series of donor- and/or acceptor-substitute d tetraethynylethenes (TEEs, TEE = 3,4-diethynylhex-3-ene-1,5-diyne) w as conducted by means of electrochemical analysis and ab initio calcul ations to determine the ability of the conjugated carbon core to promo te electronic communication between pendant functionality. The electro nic behavior as a function of the degree and pattern of Substitution w as examined and compared to the theoretical results. Experimentally, t he study indicates that the electrochemically generated charges locali ze, since the presence of one redox center on the TEE core has a minim al effect bn the redox characteristics of the other centers. Upon redu ction of p-nitrophenyl-substituted TEEs, however, a decrease in bond l ength alternation in the TEE core and a corresponding increase in the phenyl rings were predicted by ab initio calculations. This cumulenic/ quinoid structure was validated experimentally by the electrochemical isomerization of -butyldimethylsilyl)oxy]methyl}hex-3-ene-1,5-diyne t o its trans-isomer during cyclic voltammetry. Thus, the findings show that although the multiple p-nitrophenyl redox centers present on the TEE core apparently behave independently from one another in electroch emical reduction steps, delocalization of the incurred charges is effe ctively conveyed by the alkynes into the carbon framework. This deloca lization imparts a sufficiently high single bond character to the cent ral TEE double bond in the dianion to allow rotation and cis-trans-iso merization.