Resonance Raman spectroscopic and density functional theoretical study of dynamical structures of Cu(II)-bisacetylacetone

► Most of the A-band (∼290 nm band) resonance Raman spectra of Cu(AA)2 are assigned to the fundamentals, overtones and combination bands of about 9 Ag totally symmetry and 2 B1g symmetry vibrations, while most of the B-band (∼240 nm band) resonance Raman spectra are assigned to the fundamentals, overtones and combination bands of about 9 Ag totally symmetry vibrations. ► The A- and B-bands structural dynamics of Cu(AA)2 in methanol solution were revealed to be significantly different. The A-band structural dynamics is along both the photophysically important CγCβ/CβCα symmetric stretch (ν7) reaction coordinate and the photochemically important Cu-O stretch (ν11) reaction coordinate, while the B-band structural dynamics is mainly along the photochemically important Cu-O stretch (ν11) reaction coordinate, which correlates to the CuL2 → CuL + L photodissociation reaction mechanism. ► The appearances of ν23 (B1g) and ν20 (B1g) vibrational modes in the A-band resonance Raman spectra indicate that the 1 2B3u excited state is certainly coupled to some nearby 2B2u states that is within or not far away from the Franck-Condon region.