Electronic spectra of azanaphthalenes: Mixed crystal spectra of quinoxaline and quinoxaline-d6

The following spectra have been measured at 4 K, in three polarizations: ${}^1\text{B}{}_1\text{(n,π}{}^1\text{) ←}{}^1\text{A}{}_1$ absorption of quinoxaline in durene, durene-d₁₄, naphthalene and naphthalene-d₁₀, and of quinoxaline-d₆ in durene and naphthalene. The polarized phosphorescence of quinoxaline-d₆ in durene is also recorded.The analyses permit unusually extensive assignments of excited state vibrational frequencies. Also noted are various crystal effects: isotope shifts, modification of molecular frequencies, prominence of Herzberg-Teller origins, site splittings, effects of perdeuterated hosts, and polarization ratios. An unusual line-splitting seen in durene is analyzed as a resonance between coincident a₁ and b₁ vibrations of the quinoxaline molecule, coupled through the exciton bands of the host.