Table 3. Emission energies (E_emiss) and relative energies (E_rel) calculated ^a for the S₁ state in the semi-planar (S₁p) and twisted (S₁t) geometries of 8 in different environments.

ε r b	E rel c (eV)	E emiss/λmax (eV/nm) S1p d	E emiss/λmax (eV/nm) S1t e	Experiment Eemiss/λmax (eV/nm)
1.0	0.92	2.627/472	3.200/387
2.2	0.67	2.654/467	2.903/427	2.945/421
38.6	0.26	2.687/461	2.204/562	2.643/469
80	0.19	2.730/454	2.126/583	2.123/584

^aCalculated by ADC(2) employing the def2-TZVP basis set.

^bDielectric constant.

^cThe energy difference E_rel = E(S₁p) – E(S₁t).

^d S₁p: r(CO) = 1.297 Å, deviation from the planarity 12 and 8 deg, dipole moment μ = 2.1 D.

^e S₁t: r(CO) = 1.238 Å, deviation from the planarity 89 and 91 deg, dipole moment μ = 22.5 D.