In Search of Flexible Molecular Wires with Near Conformer-Independent Conjugation and Conductance : A Computational Study

• Oligomers of 1,4-disila/germa/stannacyclohexa-2,5-dienes as well as all-carbon 1,4-cyclohexadienes connected via E-E single bonds (E = C, Si, Ge, or Sn) were studied through quantum chemical calculations in an effort to identify conformationally flexible molecular wires that act as molecular "electrical cords" hang conformer-independent conjugative and conductive properties. Our oligomers display neutral hyperconjugative interactions (sigma/pi-conjugation) between adjacent sigma(E-E) and pi(C=C) bond orbitals, and these interactions do not change with conformation. The energies and spatial distributions of the highest occupied molecular orbitals of methyl-, silyl-, and trimethylsilyl (TMS)-substituted 1,4-disilacyclohexa-2,5-diene dimers, and stable conformers of trimers and tetramers, remain rather constant upon Si-Si bond rotation. Yet, steric congestion may be a concern in some of the oligomer types. The calculated conductances for the Si-containing tetramers are similar to that of a sigma-conjugated linear all-anti oligosilane (a hexadecasilane) with equally many bonds in the conjugated paths. Moreover, the Me-substituted 1,4-disilacyclohexadiene tetramer has modest conductance fluctuations with Si-Si bond rotations when the electrode-electrode distance is locked (variation by factor similar to 30), while the fluctuations under similar conditions are larger for the analogous TMS-substituted tetramer. When the electrode-electrode distance is changed several oligomers display small conductance variations within certain distance intervals, e.g., the mean conductance of TMS-substituted 1,4-disilacyclohexa-2,5-diene tetramer is almost unchanged over 9 A of electrode-electrode distances.

Ämnesord

NATURVETENSKAP  -- Kemi -- Fysikalisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Physical Chemistry (hsv//eng)

Nyckelord

Main-Group Thermochemistry

Density-Functional Theory

Noncovalent Interactions

Cross-Hyperconjugation

Excitation-Energies

Matrix-Isolation

Building-Block

Silicon

Gold

Approximation

Chemistry with specialization in Organic Chemistry

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