Comparison of CC Triple and Double Bonds as Spacers in Push–Pull Chromophores

Abstract

AbstractWe report the synthesis and properties of two series of homologous donor–acceptor (D–A) chromophores in which N,N‐dimethylanilino (DMA) or N,N‐dihexylanilino (DHA) donors and dicyanovinyl acceptors are separated by up to four C≡C triple‐bond spacers or up to three C=C double‐bond spacers. The intramolecular charge‐transfer (CT) interactions of the new D–A oligoynes and the known all‐trans D–A oligoenes were investigated by X‐ray crystallography, electrochemistry, UV/Vis spectroscopy, and theoretical calculations. In both series, the optical and electrochemical HOMO–LUMO gaps decrease with increasing spacer length. The HOMO–LUMO gaps for the D–A oligoynes and oligoenes with a given spacer length are nearly identical. The effect of the spacer length was found to level‐off for spacers with more than six carbon atoms. The third‐order optical nonlinearity of both series of molecules was determined by measuring the rotational averages of the third‐order polarizabilities γrot by degenerate four‐wave mixing.