TWO-PHOTON SPECTRUM OF BIPHENYL

Author Institution: Department of Chemistry, University of California; Department of Chemistry, Wayne State UniversityA tunable dye laser has been used to investigate the two-photon absorption of biphenyl and related compounds. The method used is the absorption of two identical photons, of either linear or circular polarization, with fluorescence detection. This provides sufficient information to distinguish totally symmetric electronic transitions $(A_{g} \leftarrow A_{g})$ from other allowed types of two-photon transitions $(B_{g} \leftarrow A_{g})$. We see two distinct bands. The lower one (33 100 to $38 000 cm^{-1}$) is due to a $^{1}B_{g}$ excited state, which is the lowest excited singlet of the molecule. The upper one (38 000 to $40 000 cm^{-1}$ and beyond) seems to be due to a $^{1}A_{g}$ excited state. No published calculation on biphenyl predicts this result