Nishihara Taishi, Segawa Yasutomo, Itami Kenichiro, Kanemitsu Yoshihiko
†Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
‡Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan.
J Phys Chem Lett. 2012 Nov 1;3(21):3125-8. doi: 10.1021/jz3014826. Epub 2012 Oct 12.
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.
环形共轭分子，即环对亚苯基（CPPs），是具有对位连接的苯环简单序列，具有理想的无边缘准一维结构。在此，我们报告了通过单光子和双光子激发光谱法阐明的[n]CPPs（n = 9、12、14、15、16）的光学性质。我们表明，在该体系中，最低未占分子轨道（LUMO）态与最高占分子轨道（HOMO）态具有相同的对称性，并确定了光学禁阻的HOMO-LUMO能隙的跃迁能量。发现HOMO-LUMO跃迁能量的环长依赖性与光致发光（PL）能量的环长依赖性相同，并且声子辅助跃迁导致高效的PL。
