| Abstract: | Starting from the octameric poly(triacetylene) (PTA) oligomer 1e as a large `macromonomer', the monodisperse tetracosamer (24‐mer) 1h was prepared by a previously introduced statistical deprotection‐oligomerization sequence (Scheme). It is the longest known molecular rod featuring a fully conjugated, non‐aromatic all‐carbon backbone. Matrix‐assisted laser‐desorption‐ionization time‐of‐flight (MALDI‐TOF) mass spectrometry was particularly useful in the characterization of oligomer 1h and clearly demonstrated its monodispersity (Fig. 1). In an effort to further clarify the conformational preferences of PTA oligomers, the X‐ray crystal structure of the 3.2‐nm‐long tetramer 1c was solved (Figs. 2 – 4). In the solid state, the C=C bonds in 1c all adopt the s‐trans conformation with respect to the buta‐1,3‐diynediyl moieties. The π‐conjugated system is perfectly planar, with the squared sum of the deviations of the backbone C‐atoms from the best plane amounting to 0.077 Å2. Analysis of the crystal lattice revealed a layered structure, in which the π‐conjugated backbone of one oligomer is insulated by the trialkylsilyl groups of adjacent oligomers in neighboring layers. |
