Lecture 5 oms

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Lecture 5 oms

  1. 1. Lecture V. . Organic Conductors Charge-transfer Complexes and Radical-ion Salts Other Low-dimensional materials Polymers
  2. 2. •Conductive organic molecules •“Plastic can indeed, under certain circumstances, be made to behave very like a metal - a discovery for which Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa are to receive the Nobel Prize in Chemistry 2000”.
  3. 3. •Molecular building blocks Single bond: sp3 hybridization Double bond: sp2 hybridization •p-AO o f neighborng i caronb atoms form π-bonding •Rigid bond, length of 134 pm  Carbon atom can form four σ-bonds.  Free rotation is possible with activaton i energy of 0.1 eV.  Bond length 154 pm
  4. 4. •Molecular building blocks  Cyclic polyenes with conjugation •that spreads the entire ring are •called aromatic or arenes  Stability and delocalization of π- •electrons maintained in fused •rings (polycyclic aromatic molecules)
  5. 5. •Molecular building blocks  Molecules with more than one double bond called polyenes.  Shape and properties of the molecule depend on the position of the double bond  Conjugated double bonds play a particular role as π-electrones are delocalized over the extent of the conjugation Isolated double bonds Conjugated double bonds Cumulated double bonds
  6. 6. •Molecular building blocks  Molecules with smaller or larger rings or other atoms in the •ring (heterocycles) possess the same delocalization •properties if the number of π-electrons is six. •Cyclopentadiene anion •Cycloheptatriene cation •Heterocycles
  7. 7. •Molecular building blocks  Molecules with a triple bond are called alkynes  Here, the π-electrons form a cylindrical cloud around σ- bond  Very rigid, linear bond with the length of 120 nm  Conjugated triple bonds show the same delocalization as double bonds Acetlene y
  8. 8. •Molecular wires  Molecular wires are, generally, rod-like structures with delocalized p-system, •the longer the structure the lesser the difference between the frontier orbitals •and the Fermi level of the electrode  polyene – alternating system of single and double bonds;  polythiophene  polyphenylenevinylene  polyphenyleneethynylene  thyophenylsubstituted benzene
  9. 9. Conductivity Of Organic Materials
  10. 10. There are Thermally-stable Good Insulators
  11. 11. We will concentrate on the good conductors
  12. 12. Charge Transfer Complexes
  13. 13. Radical-Ion Salts
  14. 14. Discovery of Conducting Organic Crystals
  15. 15. TTF-TCNQ Uniform segregated stacks (1D system) Metallic conductivity Metal-insulator transition at TMI = 54 K
  16. 16. TTF-TCNQ ANALOGS S S S S Se Se Se Se Se Se Se Se TSF HMTTF HMTSF HMTTF-TCNQ TMI = 48, 43 K 2.38a x 2.78b x c r = 0.72 HMTSF-TCNQ T = 24 K Toward semi-metal a x 2.7b x c with r = 0.74 TSF-TCNQ : TMI = 29 K 2a x 3.15 b x c r = 0.63 TCNQ is not necessary ! Cation radical salts with spectator anions (Brˉ, BF4ˉ, ClO4ˉ, PF6ˉ, …) obtained by chemical (Br2, I2, …) or electrochemical oxidation (electrocristallization)
  17. 17. Other Low Dimensional Materials
  18. 18. Conductivity is controlled by the phthalocyanine ring. The metal core does not interfere the conductivity. Phthalocyanine channel I-
  19. 19. Chain length: Si:12030 Ge: 7440 Sn:10040
  20. 20. Polymers
  21. 21. Insulating Polymeric Donor Molecules
  22. 22. Some Chemical Types of Polymers
  23. 23. Conjugated Polymers
  24. 24. Polyacetylene
  25. 25. Electrical conductivity of polyacetylene Cis-PA s = 1.7 x 10-9 S/cm Trans-PA s = 4.4 x 10-5 S/cm I2 doped s = 5.5 x 102 S/cm AsF5 doped s = 1.2 x 103 S/cm Electrochemical Oxidation s = 1 x 103 S/cm Li doped s = 2 x 102 S/cm Na doped s = 101-10-2 S/cm
  26. 26. Polyparaphenylene (PPP)
  27. 27. Polyaniline (PANI) Conductor Insulator
  28. 28. Conductivity Of Organic Materials

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