Читать книгу Handbook of Aggregation-Induced Emission, Volume 1 - Группа авторов - Страница 36

(CAAC^Ad)CuCl (see Figure 2.3) is a two‐coordinate Cu(I) complex, which exhibits highly efficient fluorescence in aggregate [50]. The excited‐state decay dynamics for (CAAC^Ad)CuCl in both solution and solid states is studied by the hybrid QM/MM approach, coupled with the TVCF rate formalism [42]. Analyzing the geometrical changes between S₀ and S₁ upon excitation, it is found that the complex is more flexible in solution. The largest changes appear in the coordination bond angles between copper and two ligands with ∠C₁−Cu−Cl, ∠Cu−C₁−N, and ∠Cu−C₁−C₄ decreasing from 9.67°, 12.82°, and 10.73° in solution to 3.66°, 4.46°, and 6.75° in the solid phase, respectively. And the transition character changes from metal‐to‐ligand charge transfer (MLCT) to hybrid MLCT and halogen‐to‐ligand charge transfer (XLCT) upon aggregation. The k_r are close in both phases, while k_ic decreases by about 3 orders of magnitude from 8.38 × 10⁷ to 1.47 × 10⁴ s⁻¹ (see Table 2.2). The λ_total decreases a lot from solution (7121 cm⁻¹) to solid state (2274 cm⁻¹). It is found that the largest contributions to λ_total come from several low‐frequency bending modes and one high‐frequency stretching mode in solution. These low‐frequency modes are assigned to be the bending vibrations associated with coordination bonds C₁−Cu and Cu−Cl, and the high‐frequency mode belongs to the stretching vibration of the C−N bond in carbene ligand. Upon aggregation, the vibrations of angles C₁−Cu−Cl and Cu–C1–N are restricted largely, while the stretching vibrations of the C₁−N bond are insensitive to the environment (Figure 2.4c). Overall, the strong solid‐state fluorescence of (CAAC^Ad)CuCl is induced by removing the nonradiative decay channels owing to the decoupling between transition electron and the bending vibrations of coordination bonds (see Figure 2.2d).

Figure 2.4 Calculated reorganization energies versus normal mode of (a) HPS, (b) TPA, (c) (CAAC^Ad)CuCl, and (d) COTh in both gas/solution and solid phases, respectively.