Photochemistry and Photophysics of Coordination Compounds

84 N. Armaroli et al.
Fig. 13 Absorption spectra of [Cu(1)2] + (full black line), [Cu(4)2] + (dashed line) and
[Cu(5)2] + (full grey line) in CH2Cl2 solution at room temperature
Fig. 14 Ligands 4 (2,9-di-p-tolyl-1,10-phenanthroline), 5 (2,9-bis(3,5-di-tert-butyl-4methoxyphenyl)-1,10-phenanthroline),
6 (2,9-Diphenyl-3,4,7,8-tetramethyl-1,10-phenanthroline)
bisphenanthrolines. In general, at least three MLCT bands can be identified
in the VIS spectral region [68]. They are termed band I (above 500 nm), band
II (maximum around 430–480 nm, the most prominent, attributed to S0→S3
transitions [61]), and band III (390–420 nm, often hidden by the onset of
band II). The envelope of such MLCT bands defines the shape of the VIS absorption
spectrum (400–700 nm). Spectral intensities are strictly related to
the symmetry of the complex (D2d vs. D2, Fig.15)that,inturn,isaffectedby
the distortion from the tetrahedral geometry (see above).