The Electronic Spectra of Crystalline Toluene, Dibenzyl, Diphenylmethane, and Biphenyl in the Near Ultraviolet

Abstract

The electronic absorption spectra of single crystals of toluene, dibenzyl, diphenylmethane, and biphenyl have been photographed at 20 °K. using polarized light in the range 3000 to 2500 Å. The fluorescence spectrum of biphenyl has also been examined. This is the first time that the excited states of biphenyl analogous to the B2u state of benzene have been observed. The main features of the spectra are similar for all four compounds, and the differences may be understood in terms of the weak coupling between the benzene rings of the "double molecules".

The electronic spectra of diphenyl and its sterically hindered derivatives

“…These measurements indicate that the 'hidden' transition should have an Emax value in the region of 700 [32]. Transitions to these low energy states must also be the source of the low intensity band with vibrational fine structure which appears when the conjugation band is blue-shifted in hindered diphenyl derivatives, [22,23] report bands at 33 340cm -1 (4.13 ev Big) 33 714cm -1 (4.18ev B2u). (The symbols B3g and Blu of references [22,23] are respectively Bag and Beu in the notation adopted here.)…”

“…With regard to the energy of this transition, it is unfortunate that spectra of crystalline diphenyl [22][23][24][25][26] have not included a measurement of this band. However, Dale [27] has measured the spectrum of solid diphenyl by the pressed KCl-disc technique and finds an intense structureless band with a maximum at 2530 i. Suzuki [1] has corrected this Amax value for the ' normal red shift' [27] observed when samples are measured in KC1 discs, and suggests that planar diphenyl --in the absence of intermolecular interactions--should show the characteristic conjugation band absorption at 2495 3,=4.97 ev.…”

“…Transitions to these low energy states must also be the source of the low intensity band with vibrational fine structure which appears when the conjugation band is blue-shifted in hindered diphenyl derivatives, [22,23] report bands at 33 340cm -1 (4.13 ev Big) 33 714cm -1 (4.18ev B2u). (The symbols B3g and Blu of references [22,23] are respectively Bag and Beu in the notation adopted here.) The order of these states is the opposite of that calculated, but since both the measured and calculated energy separations are very small this is not very surprising.…”

“…At 0= 90 ~ the situation is not so simple the 1B2 excited state being composed essentially of a mixture of four transitions from degenerate highest occupied to degenerate lowest unoccupied Hfickel MO's. The conjugation band is found to be long-axis polarized, a fact about which there is general experimental agreement[1,22,23]. Downloaded by [The University of Manchester Library] at 07:15 20 December 2014 …”

Fundamentals of Electronic Spectroscopy

“…The analysis of the electronic spectra of a diphenylmethane crystal at low temperatures (Coffman andMcClure 1958, McClure 1958) revealed a weak absorption band 145 cm −1 above the origin of the first absorption band, which was attributed to the upper member of the exciton pair. An excited-state geometry of C 2 symmetry was inferred with a very similar geometry to that of the ground electronic state.…”