Magnetic circular dichroism of peralkylated tetrasilane conformers

doi:10.1073/pnas.0403209101

Magnetic circular dichroism of peralkylated tetrasilane conformers

Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215

Contributed by Josef Michl, May 6, 2004

Abstract

Magnetic circular dichroism (MCD) of five peralkylated tetrasilanes (1–5) conformationally constrained to angles ranging from nearly 0° to 180° and of the open chain tetrasilane Si₄Me₁₀ (6) shows a clear conformational dependence and permits the detection of previously hidden transitions. In the tetrasilane CH₂Si₄Me₈ (1), with the smallest dihedral angle, comparison of MCD with absorption spectra reveals four low-energy electronic transitions. In the tetrasilanes 2–4, three distinct transitions are apparent. In tetrasilanes 5 and 6, MCD reveals the very weak transition that has been predicted to be buried under the first intense peak and to which the anomalous thermochromism of 6 and other short-chain oligosilanes has been attributed.

Footnotes

↵ † To whom correspondence should be addressed. E-mail: michl{at}eefus.colorado.edu.
Abbreviations: TD, time-dependent; DFT, density functional theory; B3LYP, Becke three-parameter hybrid functional combined with Lee–Yang–Parr correlation functional; DZ, double zeta; MCD, magnetic CD; MM3, molecular mechanics 3.