|
Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. January 2003, Volume 2, Number 1, 14-23 |
Theoretical Study on Photoinduced Color Change and Charge Transfer
of Methylviologen
Toshimasa Ishida, Makoto Murakami, Go Watanabe, Hirofumi Yoshikawa, and Shin-ichi Nishikiori
Internet Electron. J. Mol. Des. 2003, 2, 14-23
|
Abstract:
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 TDDFT scheme
reproduces the observed spectra better than the CIS scheme, but the
latter scheme is still valuable to evaluate qualitative feature of spectra.
|