Benzo- and Naphthopentalenes: Syntheses, Structures, and Properties

Benzo- and naphthopentalene
derivatives were synthesized, and the
effects of structural variations on their antiaromaticity and optoelectronic
and electrochemical properties were examined experimentally and theoretically
in detail. The results unveiled that with increasing the bond order
of the carbon–carbon bond ([5,6] junction) shared by the pentalene
and aromatic moieties, the 8π antiaromatic character of pentalene
is enhanced and the HOMO–LUMO gap is decreased, which accompanies
both the elevation of the HOMO level and the lowering of the LUMO
level. The ethynylene units between the pentalene skeleton and the
phenyl groups proved to extend π-conjugation sufficiently.