Development of cComputing system for predicting photophysical properties of transition metal compounds

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Intensely emissive transition-metal compounds have been paid attention as novel devises such as organic light emitting diodes recently. Strong phosphorescence of these compounds originates from strong spin-orbit coupling of p or d orbitals of transition metal ions. In this work, a program, which allows calculating photophysical properties such as radiative rate or zero-field splitting of relatively large molecules containing heavy transition-metals, has been developed based on time-dependent density functional theory. The calculated zero-field splitting and oscillator strength of triplet sublevels of Ir(ppy)3 and [Ru(bpy)3]2+ are in good agreement of the observed ones. Furthermore, it is demonstrated that the mechanism of phosphorescence of these metal compounds are well rationalized in terms of M-bpy sub-unit model with C2v point group.Although it has been argued for a long time whether the excited state in [Ru(bpy)_3]^<2+> is localized, the electronic configuration in the single crystals is still under debate. In this work, phosphorescence spectra of [Ru(bpy)_3]^<2+> were calculated using a harmonic oscillator approximation of adiabatic potential surfaces obtained by DFT. The spectrum simulation revealed that the phosphorescent state of [Ru(bpy)_3]^<2+> was localized ^3MLCT in a single crystal as well as in a solution and a glass matrix. However, due to strong vibronic coupling between localized MLCT states along high-frequency C-C stretching vibrational modes, simple adiabatic picture such as localized MLCT is partially broken and their vibrational wavefunctions are somehow mixed.In the photostability or photoreactivity of the highly luminescent d6 metal compounds, higher-lying triplet dd excited states are known to play very important rules. In this work, the deactivation of MLCT in [Ru(bpy)_3]^<2+> was investigated by computational chemistry. The structures of the dd states and the potential energy curves involving the deactivation pathways were determined.