STRUCTURAL PROPERITES AND ELECTRONIC STATES OF THE ELECTROGENERATED ?-DIANIONS OF ORGANIC MOLECULES

摘要

Structural and spectral characteristics of the electrogenerated tetracyanoethylene dianion (TCNE~(2-)) were experimentally and theoretically examined. Spectroelectrochemistry of TCNE gives the spectra of TCNE~(2-) in CH_3CN at 220 nm, and in CH_2Cl_2 at 300 nm. The bands in CH_3CN and in CH_2Cl_2 are assigned to the degenerate ~1E ←~1A_1 transition at the D_(2d) structure and the ~1B_(2u) ← ~1A_g transition at the D_(2h) structure, respectively. The rotational barrier of the C=C bond in TCNE~(2-) is estimated by HF, MP2 and MP4 calculations with 6-31G(d), 6-31+G(d) and 6-311+G(d) basis sets as 42-51 kJ mol~(-1). The calculations reveal that the two-electron addition to the antibonding LUMO of TCNE causes an easy rotation around the C=C bond of TCNE~(2-) characterized by the formal single bond. These results show that solvent nature significantly affects the conformational preference of TCNE~(2-) by virtue of the easy rotation around the C=C bond.