| Abstract
| - Recently, X-ray crystallographic evidence of quinoidal charge delocalization in poly-p-phenylene cation radicalswas reported [Banerjee, M. et al., J. Am. Chem. Soc.2007, 129, 8070]. In this paper, direct visual evidencefor quinoidal charge delocalization in quaterphylene (QP) is shown with three-dimensional (3D) chargedifference densities. It was revealed that the extra positive charge mainly localized on the two center units atthe ground state, while the extra positive charge will delocalize to the two outer units upon electronic statetransitions by photoexcitation. The 2D plots together with the corresponding charge difference densities wereinterpreted as large distance−charge oscillations, implying that in the positive species upon excitation a nearlyfree oscillating motion of a hole occurs. For the QP cation radical, the transition dipole moment of S1 representsmesoscopic dipole antennae.
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