INTRAMOLECULAR TORSIONAL MOTIONS DYNAMICS AND APPLICABILITY

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INTRAMOLECULAR TORSIONAL MOTIONS - DYNAMICS AND
APPLICABILITY

• Ljupco Pejov
• Institute of Chemistry, Department of Physical
  Chemistry, Faculty of Science, Sts. Cyril and
  Methodius University, Skopje, Macedonia

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Ljupco Pejov, Manuela La Rosa and Ljupco Kocarev
DYNAMICS OF THE CENTRAL PHENYLENE RING
TORSIONAL MOTION IN PHENYLENE ETHYNYLENE
OLIGOMERS. A QUANTUM-THEORETICAL CONTRIBUTION TO
THE STUDY OF CONFORMATIONAL BASIS FOR
SINGLE-MOLECULE SWITCHING PHENOMENAChemical
Physics, in press.
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THE ULTIMATE MINIATURIZATION

• DEVICES CONSISTING OF INDIVIDUAL MOLECULES

• TOP-DOWN APPROACH

• BOTTOM-UP APPROACH

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• Among the numerous basic components of
  contemporary memory and logic devices, switches
  are of particular importance.

• With the pronounced tendency for miniaturization
  of electronic devices, the need for
  molecule-based switching devices is
  self-understood. It has been recently shown that
  certain molecular systems manifest switching
  behavior

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• In general, molecular switching is an excellent
  example of the wide class of multistate phenomena
  in physical sciences.

• Two basic types of switching behavior, related to
  changes of impedance in single molecules have
  been recognized
• - The first one involves relative motion of
  molecules internal structures
• - The second is related to changes in molecular
  charge states.

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• OPE molecules

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• When all else fails, look at the Schrödinger
  equation

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ELECTRONIC DENSITY AND THE HOHENBERG-KOHN THEOREMS
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THE FIRST HOHENBERG-KOHN THEOREM
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THE SECOND HOHENBERG-KOHN THEOREM
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THE KOHN-SHAM METHODOLOGY
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FOR l 0
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l ? 0
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The DFT approach two combinations of exchange
and correlation functionals were implemented
1) combination of Beckes three-parameter
adiabatic connection exchange functional (B3)
with the Lee-Yang-Parr (LYP B3-LYP) correlation
one. 2) combination of Beckes three-parameter
adiabatic connection exchange functional with the
Perdew and Wangs 1991 gradient-corrected
correlation functional (PW91 B3-PW91). All of
the employed computational methodologies are
hybrid HF-DFT (i.e. they include an admixture of
HF exchange energy), in contrast to the pure
DFT ones.
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The LANL2DZ basis set (D95 on first row elements,
Los Alamos ECP plus DZ on Na-Bi) was employed for
orbital expansion, solving the HF or the
Kohn-Sham (KS) SCF equations iteratively for each
particular purpose of this study. The ultrafine
(99, 590) grid for numerical integration (99
radial and 590 angular integration points) was
adopted in all DFT calculations.
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Table 2. Barrier heights for the studied
oligomers (V2 / cm-1) values in parentheses in
kcal mol-1 (X halogen substitutent)
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HOMO
LUMO
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HOMO
LUMO
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Table 1. The HOMO-LUMO energy differences for the
studied oligomers (in eV)
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Table 3. Classical correlation times computed
according to the BPP approach (all values in
picoseconds)
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Table 4. Classical transition probabilities
(transition rates) computed according to the BPP
approach (all values in s-1)
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Whats next?

• External electrostatic field influence of
  stochastic conductance switching
• Considering the anionic OPE-based molecular
  species
• Applying the Greens functions approach to model
  the dynamics of charge transfer through OPE
  molecules
• ..

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THANK YOU FOR YOUR ATTENTION