Scholl Reaction of Perylene‐Based Polyphenylene Precursors under Different Conditions: Formation of Hexagon or Octagon?

A planar dibenzo‐peri‐hexacene derivative (2) was synthesized via FeCl3‐mediated Scholl reaction from a cyclopenta‐fused perylene (CP) based polyphenylene precursor (1). However, an unexpected octagon‐containing, negatively curved molecule (3) was obtained in nearly quantitative yield when 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and methanesulfonic acid (MeSO3H) were used. Similar results were observed when two smaller‐sized precursors containing one (4) or two CP units (5) were tested. X‐ray crystallographic analysis also revealed that there is no close π–π stacking between neighboring π‐conjugated skeletons. DFT calculations suggest a radical cation mechanism in the presence of FeCl3 while an arenium ion pathway for the DDQ/MeSO3H mediated Scholl reaction, which can well explain the selective formation of hexagons and octagons under different conditions. The obtained compounds showed tunable optical and electrochemical properties. [ABSTRACT FROM AUTHOR]