Electronic spectra and electronic structures of [2.2]paracyclophane and related compounds

The absorption spectra of [2.2]paracyclophane (PC), tetramethyl [2.2]paracyclophane (DD), and triple- and quadrupole-layered cyclophanes (DDD and DDDD) were measured with the n-heptane and 3-methylpentane solutions in the range of 25000–59000 cm^?1. The polarized absorption spectra of the [2.2]paracyclophane single crystal were measured in the range of 30000–50000 cm^?1 for the ab plane and 30000–37500 cm^?1 for the ac plane. Strong bands corresponding to the 180 nm band of benzene were newly observed at 53000, 49750, 49600, and 50000 cm^?1 for PC, DD, DDD, and DDDD, respectively.The electronic structures of PC, DD, DDD, and DDDD were studied semiempirically by considering the configuration interaction among the ground, locally excited and charge-transfer configurations.From the band positions, the absorption intensities, and the band polarization obtained experimentally and theoretically, we made the more reasonable and more reliable band assignments compared with those by the previous authors.