The theoretically computed electronic spectra of the studied
compounds are given in Table S6 (Supplementary data) while the experimentally
measured electronic spectra were shown in Fig. S7 (Supplementary
data). The most important electronic transitions are
shown in bold in this Table. Of the most intense transition bands predicted, the longest wavelength band at 198.1 nm (f = 0.1389),
204.2 nm(f=0.2053), 205.0 (f=0.1704) and 205.7 (0.2971) for compounds
6a–i, respectivelywere considered. Experimentally these bands
were detected at 231 nm, 234 nm, 238 nm and 239 nm, respectively.
The red shift of the experimentalwavelengths compared to the calculated
values could be attributed to the solvent effect. Themolecular orbital
energy levels involved in the above mentioned electronic transitions
and their major contributions are shown in Fig. 7.