VIII-CC-2 Crystal Structure and Spectroscopic Properties of the CT Complex of Methyl Viologen Dication and o-Dimethoxybenzene Included in a Polycyano-Polycadmate Host, and Theoretical Study on Its Red Shifted CT Absorption

Methylviologen dication is easily reduced to a monocation radical, and turned to be blue, forming a charge-transfer complex with a donor molecule. Yoshikawa et al. recently reported photo-induced reduction and charge transfer complexes in polycyano–polycadmate host clathrates. We study this reduction using quantum chemical calculations. The energy changes with the torsion angle of the two cations and the spectral change, solvent effect and the charge transfer between the dication and other guest molecules in the clathrates are investigated. The Hartree-Fock, DFT, CI singles, time dependent DFT calculations are carried out for the ground state and excited states of the two cations. Solvation effect is treated with the polarizable continuum model, and the charge transfer in the clathrates is modeled based on crystal structures determined experimentally. The optimized geometry of the monocation radical was found to be planar while that of the dication is twisted. These results are consistent with recent calculations for related compounds. The color change upon the photoreduction was reproduced by the calculation. The solvent effect of acetonitrile was found to be small. Charge transfer absorption was reproduced for the mesitylene– methylviologen dication complex in the clathrate host using a small model. The geometry modification and the color change were reproduced satisfactorily. The TDDFTscheme reproduces the observed spectra better than the CIS scheme, but the latter scheme is still valuable to evaluate qualitative feature of spectra.