Molecule in soft-crystal at ground and excited states: Theoretical approach

This account discusses first two computational methods which can be applied to electronic structure calculations of soft-crystals; one is a method composed of the periodic-density functional theory (DFT) for an infinite crystal and the post-Hartree-Fock method for a cluster model, named here cluster-model/periodic-model combined method (abbreviated as CM/PM-Combined method). The other is a quantum mechanics/periodic-molecular mechanics (named QM/Periodic-MM) method, in which a target molecule is calculated by the DFT or the post-Hartree-Fock method and the other moiety is calculated by the MM method under the periodic boundary condition. Then, the performance of these two methods is discussed. The CM/PM-Combined method exhibited good performance for investigating the gas adsorption into MOF and the QM/Periodic-MM succeeded in reproducing geometry of single crystal of platinum(II) complexes. The QM/periodic-MM method has been applied to theoretical studies of the excited state and the emission spectrum in soft-crystals: In a theoretical study of a gold(I) phenyl phenylisocyanide complex, the geometries of a triplet ligand-to-ligand charger transfer (³LLCT) and a triplet metal-metal to ligand charge-transfer (³MMLCT) excited states were optimized in the crystal and the dependences of absorption and emission energies on crystal phase were discussed. In a theoretical study of a platinum(II) dicyano bipyridine complex, the geometries of several delocalized ³MMLCT excited states, emission spectra, and their temperature dependences were investigated in the crystal. In both gold(I) and platinum(II) complexes, the characteristic features of the excited state and the emission spectra were elucidated by the theoretical calculations. Although the CM/PM-Combined method has not been applied to photochemistry issue, brief discussion is presented for its possibility for the application.