| Abstract
| - The geometries of multiply fused dehydrobenzo[12]annulenes [12]DBAs 2−7 with various topologies,which are considered as graphyne fragments, have been optimized at the B3LYP/6-31G* level of theory.Most of the optimized geometries of fused DBAs have planar structures excluding a boomerang-shapedbisDBA 4, a trefoil-shaped trisDBA 6, and a wheel-shaped DBA 7. For the boomerang-shaped bisDBA4 and the trefoil-shaped trisDBA 6, distortions originate from the steric repulsion between hydrogenatoms attached to adjacent benzene rings. The harmonic oscillator model of aromaticity (HOMA) valuesat the central benzene ring of multiply fused DBAs decrease as the number of fused 12-membered ringsincreases except for the closely related structures 4 and 5 and 6 and 7, because of bond length elongationdue to conjugation with the phenylethynyl groups. Nucleus-independent chemical shifts (NICS) werecomputed at the individual ring centers of the fused DBAs. The fusion of the antiaromatic 12-memberedrings results in increasing (more positive) NICS values at the central benzene ring, indicating the decreaseof diatropic ring currents. Furthermore, HOMO-LUMO gaps of the DBAs 2−7 are strongly influencedby the molecular topology. The para-conjugation pathway of the bis(phenylethynyl)benzene unit plays amore important role in the determination of the electronic properties of multiply fused DBAs than themeta- and ortho-conjugation pathways.
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