A new tris(tetrathiafulvaleno)dodecadehydro[18]annulene with six peripheral n-hexyl substituents was prepared by oxidative Glaser-Hay cyclization of a corresponding diethynylated tetrathiafulvalene (TTF) precursor. The electronic properties of the neutral and oxidized species were studied by both UV/Vis absorption spectroscopy and electrochemistry. From these studies, it transpires that the strongly violet-colored macrocycle does not aggregate in solution to any significant degree, which was confirmed by (1)H NMR spectroscopy. This reluctance towards aggregation contrasts that observed for related TTF-annulenes containing other peripheral substitutents. Oxidation of the TTF-annulene occurs in two three-electron steps as inferred from both the peak amplitudes and the spectroelectrochemical study. We find that the tris(TTF)-fused dehydro[18]annulene is more difficult to oxidize (by +0.20 V) than the silyl-protected diethynylated mono-TTF precursor. In contrast, the first vertical ionization energy calculated at the B3 LYP/6-311+G(2d,p) level for the parent tris(TTF)-fused dehydro[18]annulene devoid of peripheral hexyl substituents is in fact lower (by 0.44 eV). Moreover, the surface morphology of 1 d drop-cast on a mica substrate was investigated by atomic force microscopy (AFM). Crystalline domains with slightly different orientations were observed. The thickness of individual layers seen in the crystalline domains and the thickness of a monolayer obtained from a very dilute solution were determined to 1.8-1.9 nm. This thickness corresponds to the diameter of the macrocycle and the layers seen in the film are apparently formed when the molecules stack in the horizontal direction relative to the substrate.

Three new chromophores containing an electron‐donating dithiafulvene (DTF) unit attached to derivatives of retinal, diethynylethene (DEE), and dihydroazulene (DHA), respectively, are synthesized and characterized by using X‐ray crystallography as well as absorption and fluorescence spectroscopy. In general, the DTF unit induces a significant red‐shift in the lowest‐energy absorption in all investigated chromophores. The influence of the DTF unit on light‐induced cis–trans isomerization and on retro‐electrocyclization is investigated. Although the retinylidene derivative decomposes when subjected to light, the DTF‐functionalized DEE and DHA compounds undergo reversible isomerization. Computations show that the highest occupied molecular orbital (HOMO) of DTF–DHA is spread over most of the π‐conjugated system, whereas it is more localized in the ring‐opened product. This difference is reflected in the redox properties.

A selection of new acetylenic building blocks has been prepared and employed for construction of extended tetrathiafulvalenes (TTFs) and novel donor–acceptor molecules based on either diethynylethene (DEE), triethynylethene (TriEE), or tetraethynylethene (TEE) cores. The novel chromophores were studied for their redox, chromophoric, and structural properties, which have provided fundamental structure–property relationships. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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