Figure 4.

(a) Computed TD-DFT (B2PLYP/def2-TZVP) vertical excited state energies of singlet states; red lines show degenerate dark (i.e., symmetry forbidden) excited states, while black lines refer to not degenerate excited states; S_n is the dipole-allowed (B_1u) excited state (violet arrow represents the transition from the ground state), while S₁ is the first (low-lying) dark (symmetry forbidden, A_u) state. (b) Computed TDA (ωB97X-D3BJ/def2-TZVP) electronic transitions and spectra for the S₀ → S_m transitions (ground to high-lying excited states) (violet line), the S₁ → S_m transitions (transient absorption excited-to-excited states) as evaluated at the FC region (i.e., ground state S₀ geometry) (orange line), and the S₁ → S_m transitions as calculated at the relaxed (optimized, opt) S₁ geometry (dark yellow line); spectra are computed as Lorentzian function centered around the calculated TDA transitions; TDA energies are not scaled. (c) Scheme of the photoinduced relaxation mechanisms involving S₀, S_n, and S₁ states; gray arrows sketch the IC from S_n to S₁ (FC region) being the first ultrafast process and the cooling mechanisms within the S₁ state. Violet arrow indicates the ground state photoexcitation, blue arrow indicates the PA1 transition, and dark yellow and orange arrows indicate the hot and relaxed PA2 transitions, respectively. The experimental energy blue-shift of PA2 (Figure 3) is supported by the computed yellow and orange TA spectra (panel b) and sketched by the corresponding arrows (panel c).