Anisotropy of the T-T absorption spectra of naphthalene and phenanthrene

The naphthalene absorption in the spectral region of 3500–4100 Å consists of two perpendicularly polarized band systems. This can be shown by polarization measurements. The arguments given do not allow a decision as to whether or not the short axis polarized band is the ³A_g⁻ ← ³B_iu⁺ transition or an induced vibronic band of the ³B_3g⁻ ← ³B_iu⁺ transition generated by a b_3g vibration mode. The T-T polarization of phenanthrene as a function of the excitation wavenumber is quantitatively compared with the equivalent S₁ ← S₀ fluorescence polarization. There is a good agreement between the calculated and the measured curve.