Table 1.

Computed excitation energies and oscillator strengths (f)

State	MS-CASPT2	f	Experimental data
Structure I
S1	2.58 eV	0.567	446 nm (2.78 eV)*
S2	2.95 eV	<10−3	395 nm (3.14 eV)†
S3	3.64 eV	0.070
Structure II
S1	1.24 eV	0.161
S2	2.59 eV	0.115	447 nm (2.77 eV)‡
S3	2.91 eV	0.013
Structure III
S1	1.29 eV	0.122
S2	1.70 eV	0.101
S3	1.86 eV	0.008
S4	≈2.9 eV	<10−3
Structure III.P
S1	1.34 eV	0.001
S2	1.94 eV	0.008
S3	3.02 eV	0.013
Structure IV.DP
S1	2.03 eV	0.427
S2	3.06 eV	0.001
S3	3.47 eV	0.056
Structure IV
S1	3.58 eV	0.105	355 nm (3.49 eV)*
S2	3.71 eV	0.018
S3	4.23 eV	0.214

The results are compared to available experimental data. 

^*Maximum of the absorption spectra taken from refs. 1, 6, and 7. 

^† The 395-nm excitation initiates an alternative route for the PYP photochemistry (29). 

^‡ Corresponding to the low-temperature characterization of the photoproduct PYP_HL (27).