Simulations of the emission spectra of fac-tris(2-phenylpyridine) iridium and Duschinsky rotation effects using the Herman-Kluk semiclassical initial value representation method

The phosphorescent emission spectra of fac-tris(2-phenylpyridine) iridium [fac- Ir (ppy) 3] due to the lowest triplet T₁ and T₂ states are simulated using the harmonic oscillator approximation for the S0, T₁, and T₂ potential energy surfaces (PESs) and taking the Duschinsky rotation into account. The simulations involve the propagation of 177-dimensional wave packets on the coupled PES according to the Herman-Kluk (HK) semiclassical (SC) initial value representation (IVR) method. The HK SC-IVR method is employed because of its accuracy for the PES with mode mixing and its efficiency in dealing with coupled degrees of freedom for large systems. The simulated emission spectrum due to T₁ reproduces the structures of the emission spectra observed experimentally, while T₂ is found very unlikely to participate in the phosphorescent emission. Although the effect of the Duschinsky mode mixing is small for the T₁ state, neglecting it blueshifts the spectrum due to the T₂ state by 800 cm^-1 and changes the relative intensities, indicating that the importance of the Duschinsky rotation is rather unpredictable and should not be overlooked. The present simulations demonstrate that the simple harmonic oscillator approximation combined with the Duschinsky rotation can adequately describe the photophysics of fac- Ir (ppy) 3 and that the HK SC-IVR method is a powerful tool in studies of this kind.