The [2,1-a]- and [1,2-a]-isomers of fluorenofluorenedione have been synthesized via intramolecular Friedel-Crafts acylations. DFT calculations indicate that the [1,2-a]-isomer adopts a twisted, helical C-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.
An ortho-naphtho diradical! Quinoidal forms in para- and meta-patterns lie at the extremes for closed-shell and diradical forms in fluorenofluorenes, respectively. ortho-Conjugation gives an intermediate case with partial diradical character.
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