Electronic Spectrum of 2,2′-Paracyclophane

Abstract

The polarized absorption and fluorescence spectra of single crystals of 2,2′-paracyclophane at 20°K were recorded in the region 3300–3100 Å. The spectra consist of narrow lines of which 87 could be measured in absorption and nine in emission. Single crystals having two different planes developed could be prepared sufficiently thin for measurements. The spectra obtained could be divided into two components, one characteristic of a transition moment parallel and the other perpendicular to the unique axis of the tetragonal crystal. These polarization directions are characteristic of molecular directions since in this case no Davydov splitting is to be expected in view of the high symmetry of the crystal. The absorption system is analyzed satisfactorily as representing the forbidden component of the benzene 1A1g→1B2u transition in the ``dimer'' molecule. A totally symmetric progression-forming frequency of 240 cm—1 is assigned as the intermoiety vibration. The appearance of a weak 0–0 transition is interpreted as due to a small-amplitude twist of the moieties relative to one another.

Influence of an identified dimer vibration on the emission spectrum of [2,2]paracyclophane

“…This result is in agreement with conclusions drawn from polarized absorption spectra, suggesting an Au-type static distortion [16,[19][20][21] …”

“…Ron and Schnepp [16] had analyzed the absprption spectrum for species A and measured the dominant vibrational mode energy as 237 cm -1 • This value differs only by 1.5% from the value found in the fluorescence spectrum. The invariance of the normal mode frequency under electronic excitation from So to S1 is important when applying the linear approximation to the EPC theory (see below).…”

The crystal and molecular structure of 1,1,2,2,9,9,10,10-octafluoro-[2,2]paracyclophane and a reinvestigation of the structure of [2,2]paracyclophane

“…Packing forces might play a minor role in altering the distribution, but intramolecular rather than intermolecular forces appear to dominate the disordering described. A distortion of the type discussed here has been proposed for the hydrocarbon by Ron & Schnepp (1962,) on the basis of spectral data. They estimated a static twist angle of about 3 ° .…”

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

“…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.…”