[abc]-Annelated [18]annulenes

Preparation of 1,2,5,6,9,10-Hexaalkoxyhexahelicenes

“…3-Methylbenzene-1,2-diol (4) was alkylated twice under phase transfer conditions [13,14]. We used long alkyl chains to get high solubilities throughout the whole reaction sequence.…”

Synthesis of Tripyreno[2,3,4-abc: 2,3,4-ghi: 2,3,4-mno][18]annulenes

“…The diaste-reotopic protons in the C 3 conformation become enantiotopic by a ring inversion process which is fast in the NMR time scale. Like in the corresponding triphenanthro [18]annulenes [6], 12a and 12b have C 3h symmetry on average. All these NMR results were obtained by room temperature measurements of diluted solutions (about 1.5 × 10 -3 M) of 12a,b in CDCl 3 .…”

“…In contrast to the unsubstituted [18]annulene [21], the areno-condensed [18]annulenes are not planar [4,6,11]. They can be regarded as aromatic "islands" which are combined by trans configured olefinic "bridges".…”

“…However, [n]annulenes (n ≥ 10) are not suitable for applications in materials science, because their chemical stability is much too low. Aromatic ring systems as benzene [3 -5], naphthalene [6], phenanthrene [6 -11] or chrysene [12], condensed with the annulene perimeter, enhance strongly the thermal stability of these compounds. Moreover, these disc-like systems represent discotic mesogens which are a precondition for the formation of liquid crystals with discotic nematic or columnar phases [6 -11, 13].…”

“…Many areno-condensed annulenes exhibit a high tendency of aggregation in solution as well as in the neat phase [4,6,7,8,11]. Thus, bimolecular photoreactions are efficient even in highly diluted solutions, because light is being absorbed by aggregates (dimers etc.).…”