Table 1 Vertical excitation energies for each of the five excited singlet states, labelled S1–S5, with the dominant electronic character provided in parentheses, as well as the S0 → D0 ionization potential at the respective equilibrium geometries of QC and NBD and at the S1/S0 MECI geometry, calculated using RMS-CASPT2(2,6)/6-31G* + D

From: Ultrafast electronic relaxation pathways of the molecular photoswitch quadricyclane

State

QC (eV) (character)

MECI (eV) (character)

NBD (eV) (character)

S1

5.29 (3s)

0.00 (V)

5.25 (V)

S2

5.82 (3px/V)

2.74 (3s)

5.61 (3s)

S3

5.88 (3py)

3.31 (3px)

6.11 (3py)

S4

6.05 (3pz)

3.47 (3py)

6.28 (3px)

S5

7.53 (3px/V)

3.53 (3pz)

6.34 (3pz)

IP (S0 → D0)

7.67

5.26

8.02

  1. Note that the numbering of the states is directly related to the electronic structure model used. The geometries are shown in Extended Data Fig. 3. The value of the average carbon–carbon distance coordinate rCC for the three geometries is \({r}_{{{\mathrm{CC}}}}^{{{\mathrm{QC}}}}\) = 1.51 Å, \({r}_{{{\mathrm{CC}}}}^{{{\mathrm{MECI}}}}\) = 1.98 Å and \({r}_{{{\mathrm{CC}}}}^{{{\mathrm{NBD}}}}\) = 2.47 Å. At the QC ground-state geometry, in the two mixed states S2 and S5, the 3px component is dominant in S2 and the valence (V) component is dominant in S5.
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