title: Excited States in Cycloparaphenylenes: Dependence of Optical Properties on Ring Length.
abstract: Hoop-shaped conjugated molecules, cycloparaphenylenes (CPPs), are simple strings of benzene rings with para linkages that have an ideal quasi-one-dimensional structure without edges. Here, we report optical properties of [n]CPPs (n = 9, 12, 14, 15, 16) clarified by one- and two-photon excitation spectroscopy. We showed that in this system the lowest unoccupied molecular orbital (LUMO) state has the same symmetry as the highest occupied molecular orbital (HOMO) state, and determined the transition energy of the optically forbidden HOMO-LUMO gap. It is found that the ring-length dependence of the HOMO-LUMO transition energy is identical to that of the photoluminescence (PL) energy, and that phonon-assisted transition causes efficient PL.
authors: †Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors: Taishi
authors: T
authors: Nishihara
authors: ‡Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan.
authors: Yasutomo
authors: Y
authors: Segawa
authors: ‡Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan.
authors: Kenichiro
authors: K
authors: Itami
authors: †Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors: Yoshihiko
authors: Y
authors: Kanemitsu
keywords: cycloparaphenylenes; electronic structure; exciton; luminescence; two-photon excitation spectroscopy