The electronic spectra of diphenyl and its sterically hindered derivatives

Abstract

The electronic energy levels of diphenyl have been calculated by a Pariser, Parr and Pople method for angles between the two benzene rings of 0 ~ 45 ~ and 90 ~ . All singly but no doubly excited states have been considered. The results are compared with the electronic spectra of diphenyl and its sterically hindered derivatives and with the circular dichroism spectra of optically active diphenyl derivatives.Satisfactory agreement with experiment is found except for the calculated and measured rotational strengths. The results of the present work are compared with those of the ' molecules in molecules ' method.

New experimental information from two-photon spectroscopy and comparison with theory

“…In earlier investigations (26,27,28) it is assumed that 2A lies somewhere around the beginning of the second strong OPA which means at least 7.000 cm higher in energy than it is now located. Our SCI calculation (Fig.…”

“…The OPA spectrum (Fig. 4a) consists of only two broad bands with maxima at 40.500 and 49.500 cm1, which can be assigned to B2-transitions (26). From comparison with fluorene and also o-methylated biphenyls (27) it is, however, known that a further band (called H-band) is hidden under the long wavelength tail of the first B2-band.…”

π-SCF and INDO calculations and the absorption, polarized excitation and circular dichroism spectra of [4]-helicenes

“…The 7r-SCF transition energies of [4]-helicene are generally too large by ,,~ 5000 cm -1 (table 1) and these energies are not significantly improved by allowing for the variation in the rr-resonance integral with bond-length [18] nor with the angle of torsion about the bond according to the cosine relation [17]. The lowering of the energy of a predominantly 7r-excited configuration in the INDO treatment is, however, approximately proportional to the a content for small admixtures.…”

“…371 eV) and by adopting the method of Grinter [17] for the estimation of electron repulsion integrals in non-planar ~r-electron systems. The resonance integral was taken to vary with bond-length, through the w-electron bond-order, according to the relation given by Coulson and Golebiewski [18].…”

Quantum Theory of Atoms and Molecules

“…The resonance integral (3i, was often fixed in these calculations, in a way depending mainly on the nature of the atoms; more successful, however, have been the calculations which involve the dependence of {3ij on the bond length, e.g., through a linear dependence on the mobile bond order, Pi; (373, 375,383) or an exponential relation fl., = A exp (-Bpij) (376)(377), through a proportionality to the overlap integral (374, 378,379,380) or, ex ceptionally, according to Kon's (381) formula, {3W,.,Rir6 (382).…”