Two-photon spectroscopy of antiaromatic molecules: the case of biphenylene

Abstract

The two-photon spectrum and polarization ratio of biphenylene have been measured at room temperature in the spectral range 225–370 nm, combining fluorescence-excitation and thermal-lensing techniques. The first excited Ag state 2Ag, has been observed around 265 nm and the second excited B1g, 2B1g, has its onset at ≈ 225 nm. Similarities and differences with alternant aromatics are pointed out. MO calculations of two-photon intensities support the interpretation of the experimental data.