Synthesis and Electronic Properties of Fluoreno[2,1‑<i>a</i>]fluorenedione and Fluoreno[1,2‑<i>a</i>]fluorenedione

The [2,1-<i>a</i>]- and [1,2-<i>a</i>]-isomers of fluorenofluorenedione have been synthesized via intramolecular Friedel–Crafts acylations. DFT calculations indicate that the [1,2-<i>a</i>]-isomer adopts a twisted, helical <i>C</i>₂-symmetric structure and that its protonated form is the thermodynamic product of the Friedel–Crafts acylation in hot sulfuric acid. Absorption spectroscopy and cyclic voltammetry measurements provide experimental estimations of frontier molecular orbital energy levels, which are reported and discussed