html5-img
1 / 57

Cobalt- bis(Dioxolene ) Valence Tautomers : Molecular Properties and Progress toward Devices

Cobalt- bis(Dioxolene ) Valence Tautomers : Molecular Properties and Progress toward Devices David A. Shultz,* 1 Robert D. Schmidt, 1 Will Rice, 2 Frank Tsui, 2 Marco Buongiorno-Nardelli 3 and Arrigo Calzolari 4 1 Department of Chemistry, NC State University, Raleigh, NC 27695-8204

gloria-mcintosh
Download Presentation

Cobalt- bis(Dioxolene ) Valence Tautomers : Molecular Properties and Progress toward Devices

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cobalt-bis(Dioxolene) Valence Tautomers: Molecular Properties and Progress toward Devices David A. Shultz,*1 Robert D. Schmidt,1 Will Rice,2 Frank Tsui,2 Marco Buongiorno-Nardelli3 and Arrigo Calzolari4 1Department of Chemistry, NC State University, Raleigh, NC 27695-8204 2Department of Physics, UNC-Chapel Hill 3Department of Physics, NC State University 4Department of Physics, University of Modena

  2. NSF CCI: Center for Molecular Spintronics (CMS) The CMS is exploring the utility of switchable/bistable paramagnetic molecules and semiconducting oligomers (based on metal complexes of semiquinones) -- as new ways to understand and to control both spin injection and spin-polarized transport. Our approach involves a highly-integrated program consisting of: (1) synthesis and characterization of these molecules and oligomers, (2) detailed surface structure and bonding studies, (3) spin injection and transport measurements, and (4) computational modeling.

  3. Collaborative Structure to Date Shultz Group Molecule and polymer synthesis Tracy Group Nanoparticle synthesis You Group Monolayer synthesis TsuiGroup Valence Tautomer “crystal devices” Dougherty Group Nanoparticle devices Rowe Group Device characterization Jones Group Education/Outreach Buongiorno-NardelliGroup Theory/Computation

  4. New Valence Tautomers and New Studies of “Old” Valence Tautomers

  5. One quartet, one doublet One quartet, one doublet Hab -3J/4 -3J/4 Very weak superexchange across 11 bonds Very weak superexchange across 11 bonds -15J/4 -15J/4 2Hab Intramolecular ET within the mixed-valent SQ-Cat dyad promotes ferromagnetic coupling: double exchange NC STATE UNIVERSITY Using Electron Transfer to Affect “Long-Range Exchange” Coupling via Organic Double Exchange ET ET = f(Hab) Hab Hab

  6. NC STATE UNIVERSITY Using Electron Transfer to Affect “Long Range Exchange Coupling” J = +74 cm-1 (Doublet + Triplet model; 3J gap) cparaT (emu K mol-1) J ≈ +4 cm-1 (Doublet + Triplet model; 3J gap) Temperature (K) • C2h complex has p-overlap between metal/dyad that C2 complex lacks • Jis a direct measure of mixed-valent wavefunction

  7. NC STATE UNIVERSITY ORTEPs of C2h Complexes > 2 nm Phenyl ring torsions are ≈15° from SQ and NN ring planes > 1.4 nm SQ-NN torsion ≈ 15° CoIIISQ(Cat) formulation with crystallographic inversion center at Co

  8. NC STATE UNIVERSITY Magnetic Susceptibility for Low Temp Limit cparaT=1.875 3-coupled spins cpara•T (emu K mol-1) High Temp Limit cparaT=1.125 3-uncorrelated spins • Only quartet state populated at all temperatures Temperature (Kelvin)

  9. NC STATE UNIVERSITY Magnetic Susceptibility for Low Temp Limit cparaT=1.875 3-coupled spins cpara•T (emu K mol-1) High Temp Limit cparaT=1.125 3-uncorrelated spins • Quartet and doublet states populated Temperature (Kelvin)

  10. JB (11 bonds) JA (5 bonds) JC NC STATE UNIVERSITY A more sophisticated HDvV fit of the magnetic data… JA = JB = 234 cm-1 g = 2.0 (fixed) q = -2.06 K cparaT (emu K mol-1) DB DA Temperature (K) 0 234 cm-1 Q Results of trimer fit support delocalization of SQ/Cat!

  11. Electronic Structure/Spin-Dependent Delocalization Approach… NC STATE UNIVERSITY Double Exchange/Spin-Dependent Delocalization Model… Cat SQ CT band in IR region! nmax= 2Hab NN NN NN NN J J Cat SQ SQ Cat Hab Hab • vibronic structure • ∆n1/2 less than Hush prediction • weak solvent dependence • Class II/III or Class III mixed valent (DELOCALIZED) Energy (cm-1) • Hab describes delocalization of the mixed-valent dyad one set of quartets and two sets of doublets • HDvV (Heitler-London)Double exchange (Zener)singleJ only: JB = 0 Matrix elements of interacting doublets formed from local SQPhNN singlet states Double exchange:Girerd, et al.. Chem. Rev.1990, 90, 1359.

  12. Electronic Structure/Spin-Dependent Delocalization Approach… NC STATE UNIVERSITY Double Exchange/Spin-Dependent Delocalization Model… Cat SQ CT band in IR region! nmax= 2Hab Energy (cm-1) Off-diagonal blocks allow for interaction of doublet states  six state SDD model Bersuker, et al., Adv. Chem. Phys. 1992, 81, 703. Double exchange:Girerd, et al.. Chem. Rev.1990, 90, 1359;

  13. Electronic Structure/Spin-Dependent Delocalization Approach… NC STATE UNIVERSITY Cat SQ CT band in IR region! DB* nmax= 2Hab DA* 2Hab QB DB 3500 cm-1 DA Energy (cm-1) 0 QA

  14. Thermally Accessible Excited Singlet State 2J+Hab/2 2J DB* S 2J-Hab/2 D 2J DA* -J+HAB QB JSQ-Ph-NN = 100 cm-1 Hab/2 DB 0J 0J T D Q -Hab/2 -J DA JA JB -J-Hab QA Classical Double Exchange JC HDvV Kirk, M. L.; Shultz, D. A.; Schmidt, R. D.; Rodriguez, D. H.; Lee, H.; Lee, J. J. Am. Chem. Soc.2009, 131. 18304.

  15. Thermally Accessible Excited Singlet State 2J+Hab/2 DB* 2J DB* S 2J-Hab/2 DA* D 2J DA* -J+Hab QB QB JSQ-Ph-NN = 100 cm-1 Hab/2 DB DB 0J 0J T D Q -Hab/2 -J DA DA JA JB -J-Hab QA QA Classical Double Exchange Spin-Dependent Delocalization JC HDvV Kirk, M. L.; Shultz, D. A.; Schmidt, R. D.; Rodriguez, D. H.; Lee, H.; Lee, J. J. Am. Chem. Soc.2009, 131. 18304.

  16. NC STATE UNIVERSITY Evaluating Hab by both Theory and Spectroscopy State Energies calculated with J = 465 cm-1 Spectroscopic Hab Doublet Doublet Quartet Energy (cm-1) 2Hab “IVCT” nmax= 2Hab Energy (cm-1) HAB/cm-1 For Hab > ~1000 cm-1, ∆EQD is constant

  17. Electronic Structure/Spin-Dependent Delocalization Approach… NC STATE UNIVERSITY DB* DA* 2Hab QB DB J = 580 cm-1 Hab = 1750 cm-1 (fixed) g = 1.99 q = -2.06 K cparaT (emu K mol-1) 3500 cm-1 DA 229 cm-1 Temperature (K) 0 QA

  18. NC STATE UNIVERSITY Thermally Accessible Excited Singlet State DB* DB* S DA* D 2J DA* QB QB JSQ-NN ≈ 500 cm-1 DB • This gap should be larger • Doublet thermally inaccessible DB 0J T D Q DA DA QA QA

  19. NC STATE UNIVERSITY J = 580 cm-1 Strong SQNN exchange in SDD molecule(s) can be explained using VBCI model JSQNN = 100 cm-1 Kirk, M. L.; Shultz, D. A.; Schmidt, R. D.; Rodriguez, D. H.; Lee, H.; Lee, J. J. Am. Chem. Soc.2009, 131. 18304.

  20. New Valence Tautomers and New Studies of “Old” Valence Tautomers

  21. X = CN X = CN X = Br X = NO2 X = OMe X = H X = Me Buchanan, R. M.; Pierpont, C. G. J. Am. Chem. Soc. 1980,102,4951-4957. Schmidt, R. D.; Shultz, D. A.; Martin, J. D. Inorg. Chem.2010, 49, 3162-3168. Schmidt, R. D.; Shultz, D. A.; Martin, J. D.; Boyle, P. D. J. Am. Chem. Soc.2010, 132, 6261-6273.

  22. NC STATEUNIVERSITY UNC-Chapel Hill Photoinduced Conversion Thermal Conversion Low temperature values – 0.375 – Appropriate for CoIII(Cat)(SQ) High temperature values: Non-active – 0.375 →CoIII(Cat)(SQ) Active – 2.85 – 4.75 →hs-CoII(SQ)(SQ) Long-lived kinetic stability Accessibility of metastable state via thermal cycling or irradiation Schmidt, R. D.; Shultz, D. A.; Martin, J. D. Inorg. Chem.2010, 49, 3162-3168; J. Am Chem. Soc. 2010, 132, 6261-6273.

  23. c b a b • Anisotropic lattice distortions implicate C-H•••N and C-H•••O interactions • Totally symmetric Co-L stretching coupled to lattice modes cooperativity ?

  24. Variable Resistor Circuits: Constant applied bias – variable current flow Thermal-induced Photoinduced Photoinduced or Thermal-induced

  25. NC STATEUNIVERSITY UNC-Chapel Hill Current Measurement Devices VT single crystal or polymer film electrode 1 electrode 2 SiO2 base

  26. Field Effect Structures for Studying Electronic Properties of Valence Tautomer • SiOx/n-Si/Au back gate • Gate capacitance ~0.7 nF (forward bias) • Crystalline Valence Tautomer • Making contacts via solution • 10 m spacing between contacts (Van der Pauw) • Forward gate bias to access HOMO states 100 m 100 m Au contacts without sample Au contacts with sample mounted

  27. L8 (- Crystal) L5 L6 L7 • L1 (+ Gate) • to C3 on separate sample mount • (contacts back Au) L4 (+ Gate) L2 (+ Crystal) L3

  28. Electronic Transport of Tautomer source current vs. gate and source voltages at room temperature 10 9 8 7 5 3 1 Source Voltage Vs (V) Source Current(10-12 A) Gate Voltage Vg (V) • High threshold voltage (HOMO edge): 7.1 V • Low mobility (hole): 10-6 cm2/V-s

  29. A More Conductive Valence Tautomer is needed…

  30. Polymeric Pyrazine-BridgedCobalt Semiquinonate-Catecholate Complex • Photomechanical polymers that show light-induced transition between different spin states – different geometries • Potential for functional molecular spintronic devices • Synthesized (Pierpont, JACS, 1994) but not characterized so far

  31. CoIII(N-N)-(DBSQ)(DBCat) Metal Semiconductor Semiconductor Three spin configurations: Paramagnetic Ferromagnetic Antiferromagnetic Dispersive bands indicate possibility for band transport along the polymer axis Eg(Γ)up = 0.54 eV Eg(Γ)dw = 0.25 eV Eg(Γ)up = 0.30 eV Eg(Γ)dw = 0.30 eV Marco Buongiorno-Nardelli and ArrigoCalzolari

  32. Buongiorno-Nardelli

  33. New Magnetic Data

  34. NC STATE UNIVERSITY Conclusions • ElectroactiveDonor-Bridge-Acceptor biradicalscan be used to prepare double exchanged systems that show “long-range electron correlation.” • This is a general molecular architecture: mixed-valent organic dyad covalently attached to a pair of localized spins. • Molecular analog of dilute magnetic semiconductors? • Ongoing studies of valence tautomer-oriented devices

  35. NC STATE UNIVERSITY Acknowledgements Rob Schmidt UbieSullivan Geoff Lewis Cooper Dawson Professor Marty Kirk Diana Habel-Rodriguez Department of Chemistry, University of New Mexico Professor Frank Tsui Will Rice Department of Physics, UNC-Chapel Hill Professor Marco Buongiorno-Nardelli Department of Physics, NC State University Professor ArrigoCalzolari, Trieste $$$ National Science Foundation (CHE-0910585 and -0943975)

  36. Ground Configuration Excited Configuration A Quartet Quartet Excited Configuration B Quartet NC STATE UNIVERSITY VBCI model used to explain ferromagnetic exchange in biradical ligand complex suggests stronger ferromagnetic exchange in SDD molecule(s) due to more superexchange pathways

  37. NC STATEUNIVERSITY UNC-Chapel Hill Current Measurement Designs VT single crystal electrode 1 electrode 2 SiO2 base

  38. NC STATEUNIVERSITY UNC-Chapel Hill Self Assembled Monolayers of VT and Devices VT 1 Au film pyz Tet VT 1 Tet Wei You

  39. NC STATEUNIVERSITY UNC-Chapel Hill Preliminary Results SAM of Pyridine thiol made; Ligand exchange with VT 1 was attempted; it works! XPS of surfaces were carried out; it seems that pyridine thiol was not making satisfactory SAM; new molecule was proposed and to be synthesized

  40. CMS Concept Chart (Phase I)

  41. Valence Tautomer Polymer Synthesis 30 % 72% 75% 93% 95%

  42. Temperature Pressure Light Cat SQ SQ SQ CoII CoIII A CoII I CoIII CoIII Voltage, Temperature

More Related