Experimentally determined and theoretically calculated vertical (diabatic) triplet and singlet excitation energies (eV) of azobenzene and diazocine, in E and Z configurations. For computational details, see ESI.

	TDDFT	CASPT2	Exp.
Azobenzene
ΔE S0 → T1
Z	1.99	1.83	1.30–1.6 (ref. 39, 40, 42 and 43)
E	2.08	1.87 (ref. 55 and 56)	1.57 (ref. 39, 40, 42 and 43)
ΔE S0 → S1
Z	2.98	2.58	2.82
E	2.85	2.44	2.78
Diazocine
ΔE S0 → T1
Z	2.09	2.21	1.89
E	1.74	1.83	1.53
ΔE S0 → S1
Z	3.19	3.02	3.07
E	2.64	2.52	2.53 (ref. 10)