Electronic Spectrum of (2, 2)Paracyclophane. II

Abstract

The studies of the absorption and fluorescence spectra of single crystals of (2, 2)paracyclophane in the region 3300–3100 Å reported in a previous paper have been extended. Well-characterized samples with the (hk0) developed crystal plane were used. In absorption two distinct spectra were obtained in the two polarization components. The fluorescence was strongly polarized in one direction (parallel to the fourfold c axis) and represents the mirror image of the equally polarized absorption component. It was concluded that the observations prove conclusively that the differently polarized spectral components represent transitions to two different electronic states, with an energy difference of 369 cm−1. The lowest-energy transition certainly contains the 0–0 line and all available evidence supports the conclusion that also the second transition has allowed character. The only interpretation consistent with all observed features of the spectra is as follows. The two observed states are the gerade dimer states (B2g and B3g in D2h) being the out-of-phase combinations of the B2u and B1u benzene moiety states. The transitions have allowed character due to a torsional distortion of the molecule in the excited state. The interpretation is fully consistent with theoretical energy calculations.

Investigation of the excited triplet states of [2.2]- and [3.3]paracyclophane

“…Z-axis perpendicular to the subunits and take the Y-axis as the long axis so that the bridged C atoms are in the YZ-plane. This is the same convention as used by Ron and Schnepp [6]. (Not all authors use this convention, however, but take our X and Y interchanged).…”

“…Rond and Schnepp [4,6] . Without detailed experimental work it will be impossible to indicate to which species the two triplet states belong.…”

“…Somewhat later Cram et [2.2]phanes were synthesized including several isomeric naphthalenophanes, diphenylophanes, fluJrenophanes, phenanthrenophanes"pyrenophanes md others [3]. Although several papers deal with the Jhysical properties of the excited singlet and triplet ;tates ofparacyclophane [4][5][6][7][8][9][10][11][12][13][14], there are still open luestions, in particular, concerning the properties of the latter. We report in this paper on a reinvestigation )f 1 and 2 by emission spectroscopy and by optical tt Present address: Max-Planck-Institut fUr Kohlenforschung, 4330 Miilheim/Ruhr, West Germany.…”

UV/Vis Spectra of Cyclophanes

“…However, early models that were based solely on the p electron system and neglected the r core were unsatisfactory [28]. The anomalous band shape has been explained by the assumption of large structural rearrangements on excitation or emission [30][31][32]. It yielded, even on a qualitative level, a satisfactory explanation of the electronic spectra, the ESR spectrum and the photochemical behavior of such compounds.…”

“…Cram et al [9] have studied the UV spectra of [m.n]paracyclophanes in which m and n were varied stepwise, one carbon at a time from m = n = 2 (14) to m = 5, n = 6 (27,17,(28)(29)(30)(31)(32)(33)(34)(35). Some spectra are shown in Fig.…”