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Tobin J. Marks Department of Chemistry and The Materials Research Center Northwestern University. Charles E. and Emma H. Morrison Professor of Chemistry Professor of Materials Science and Engineering Vladimir N. Ipatieff Professor of Catalyic Chemistry. Biographical sketch.

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tobin j marks department of chemistry and the materials research center northwestern university

Tobin J. MarksDepartment of Chemistry and The Materials Research CenterNorthwestern University

Charles E. and Emma H. Morrison Professor of Chemistry

Professor of Materials Science and Engineering

Vladimir N. Ipatieff Professor of Catalyic Chemistry

biographical sketch
Biographical sketch
  • BS, University of Maryland, 1966
  • PhD, Massachusetts Institute of Technology, 1970, under Professor F. A. Cotton.
  • Assistant Professor at Northwestern University, 1970.
  • Numerous awards and honors.
  • Fellow, Royal Society of Chemistry
  • Member, National Academy of Sciences

Published over 800 research articles and holds 80 U.S. patents.

research activity
Research Activity
  • Organometallics
  • Photonics
  • MOCVD
  • Molecular Electronics
organometallics
Organometallics
  • Investigate the Design and Implementation of Organometallic and Main Group Complexes for Catalysis
  • Hydroelementation: Organo-f-element complexes for small-molecule catalysis
  • Olefin polymerization: Nuclearity effects in group 4 and group 13 catalyst/cocatalyst studies
hydroelementation
Hydroelementation

Very desirable yet challenging atom-economical transformation.

Transition Metals:

  • Impressive functional group tolerance
  • High temperatures and catalyst decomposition

Lanthanide Metals:

  • Efficient at room temperature with long catalyst life
  • Improving (but limited) functional group tolerance.
lanthanide catalyzed hydroamination
Lanthanide Catalyzed Hydroamination
  • Aminoalkene/alkyne hydroamination/ cyclization:

Rate = k[substrate]0[Ln]1

  • Very sensitive to stericdemands around metal center;
characteristics of hydroamination
Characteristics of Hydroamination

Hydroamination carried out on:

1,2-disubstituted internal aminoalkene, aminoallene and aminodiene.

Identical rate law for all substrates.

Rate:La>Sm>Lu (aminoalkenes).

Rate decreasing with increasing Ln3+ radius (aminoalkynes) and maximize at intermediate radius for aminoallenes (Y3+ >Sm3+ >Lu3+ >La3+ ).

chiral catalyst c 2 symmetric system
Chiral Catalyst: C2-symmetric system

Lanthanides having the largest ionic radii exhibit the greatest turnover frequencies as well as enantioselectivities.

Exhibits good rates and enantioselectivities, comparable

to or greater than those achieved with chiral C1-

symmetric organolanthanocene catalysts.

molecular electronics
Molecular Electronics
  • Research involves synthesis and study of thin-film and molecular electronic materials, focusing on the versatile thiophene-based oligomers and polymers as semiconducting and conducting layers.
  • Utilize thin film deposition techniques like spin-coating, sublimation and unique self-assembly.
  • Addressing fundamental questions of electronic structure, optical properties and charge-transport mechanism in these materials through combined synthetic and theoretical research in collaboration with Prof. Ratner.
molecular electronics14
OLED/PLED

Toward the Ideal Organic Light-Emitting Diode; nanoscale tailoring of the anode/HTL interfaces.

OTFT

Toward N-type semiconductors

Gate dielectrics for low-voltage Organic Field Effect Transistors.

Molecular Electronics
organic light emitting diode
Organic Light Emitting Diode
  • Schematic of a typical OLED heterostructure.
  • (II)Energy level diagram of a typical multilayer OLED. A and B indicate the cathode-ETL and anode-HTL interface, respectively.
importance of interface
Importance of Interface
  • Interfacial phenomena represent challenging area of OLED science.
  • Carrier transport in OLED heterostructures largely injection limited.
  • Focus on hole injection attenuation and electron flux enhancement.
  • Anode-organic interface amenable to precision modification.
  • Motivated to develop nanoscopically well defined, molecule based anode-organic (HTL) interface to remove energy discontinuity.
slide18
Characterization results from AFM, advancing aqueous contact angles, optical spectroscopy, cyclic voltammetry, XPS, UPS, and X-ray reflectivity are summarized in Table.
  • These analyses indicate, self-limiting deposition process yields conformal, largely pinhole-free, hole-transporting molecule-scale layers of subnanometer dimensions.
oled interfacial structure charge injection relationships
OLED Interfacial Structure-Charge Injection Relationships:
  • Responses of OLEDs having structure ITO/(SAM)/NPB/AlQ:1% DIQA/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/Li/AgMg. (A) Current density vs voltage. (B) Luminance vs voltage.
hydrocarbon monolayers contrasts with conventional htls
Hydrocarbon Monolayers: Contrasts with Conventional HTLs
  • ITO/n-butylsiloxane SAM/Alq OLED exhibit luminance and efficiency comparable to TAASi3 and TPDSi2 SAM based devices.
  • Alkyl based interlayers, thinner or thicker than C4 yield diminished performance.
triarylamine functionalized anodes in polymer light emitting diodes
Triarylamine-Functionalized Anodes in Polymer Light-Emitting Diodes
  • Triarylamine SAMs are transparent in the visible region while also offering enhanced hole injection.
  • Fabricate blue PLED based on PFO.
  • Maximum ext. q.e. and luminance ~ 40% and 3X greater for SAM vs PEDOT-PSS.

PLED devices: ITO/SAM or HTL/PFO/Ca/AL

slide22
SAM modified ITO anode enhances hole injection current 100X times vs bare ITO.
  • Greater IP of SAM on ITO ( revealed by UPS measurements).
  • TPD-Si2 SAM moderates discontinuity in ITO EF-PFO HOMO.
organic field effect transistors
Organic Field Effect Transistors
  • The three fundamental device components are the contacts, semiconductor and the dielectric layer, typically arranged as shown in figure.
  • Need for low voltage operating, low cost manufacture gate dielectrics.
ultrathin cross linked polymers as gate dielectrics for low voltage ofet s
Ultrathin Cross-Linked Polymers as Gate Dielectrics for Low Voltage OFET’s

Low temp fabrication, crosslinking(insolubility), ultrathin, huge k/d ratios and low leakage current.

dielectric patterning and capacitance
Dielectric Patterning and Capacitance.
  • MIM and MIS leakage and capacitance measurements carried out.
  • The current densities for CPVP-Cn and CPS-Cn films lower than for PVP and PS.
  • Ultrathin CPB’s exhibit very large capacitance values.
slide27
The excellent insulating properties of I–III are demonstrated by cyclic voltammetry.

Film pinhole assay by cyclic voltammetry using bare ITO (dotted line) and nanodielectrics III coated ITO as working electrodes (solid line).

Measurement of nanodielectric capacitance–voltage electrical characteristics at 104 Hz.

towards n type semiconductor
Towards N-type Semiconductor:
  • Semiconducting element in organic TFT’s: high mobility, stable and solution processable.
  • Unsubstituted,α,ω-, and β,β’- dialkyl substituted nTs and β-alkyl-substituted PTs.
  • Carrier mobilities and on/off ratios comparable to amorphous silicon.
  • Behave as p-type semiconductors; electron richness of thiophene.
need for n type semiconductor
Need for N-type Semiconductor
  • For full realization of the potential of organic electronics, high performance e- transporting (n-type) materials needed.
  • Enable applications, e.g. bipolar transistors, p-n junction diodes and complementary circuits.
  • Varying the substitution on thiophene backbone modulates the “band gap”.
perfluoroalkyl substituted oligothiophenes
Perfluoroalkyl substituted oligothiophenes
  • First compound: DFH-6T in 2000.
  • Intensive research towards understanding chemical, structural and physical properties as well as solid-state characteristics of five homologous series of thiophene based compounds.
optical properties
Optical properties
  • Chemical substitution has minor, but core conjugation length has marked effect.
  • Increasing number of thiophene rings and fluorocarbon substitution increase solution q.y.
  • Lower q.y. when substituents at lateral positions.
  • All oligothiophenes are conformationally more rigid in the e.s.
electrochemistry33
Electrochemistry
  • Stability of ox and red species increase with core length and substituents at end.
  • As core size increase ox and red parameters move to less +ve and –ve values; progressive reduction of electrochemical band gap.
  • ΔE1/2 value decrease with increasing core length.
field effect transistors35
Field Effect Transistors
  • All of the semiconductors investigated are FET-active, independent of the chemical substitution, regiochemistry, and core dimension.
  • All fluorocarbonsubstituted systems functionalized at the terminal thiophene units (1 and 2) are n-type semiconductors, in contrast to the uniformly p-type activity exhibited by the remaining systems 3-5.
  • Principal factors governing FET activity characteristics are related to the intrinsic positions of the molecular/solid-state orbitals/bands with respect to charge injection and transport.
slide36
Electron-withdrawing strength of the perfluoroalkyl substituents is sufficient to lower both the fluorinated-nT HOMO and the LUMO energies such that electron injection and transport becomes, in the majority of cases, more favorable than hole injection and transport.
conclusion
Conclusion:

Molecular Electronics

  • OLEDs:Triarylamine based interlayers enhance HTL adhesion and afford greater hole injection fluence, higher luminance, greater external quantum efficiency and reduced turn-on voltage.
  • Gate Dielectrics:Robust insoluble siloxane cross-linked polymeric films exhibited high capacitance and low leakage.
  • N-type Semiconductors:

Perfluorinated thiophenes were investigated and regiochemistry, core length was found to affect OFET performance.

references
References:

Organometallics:

Hong, S.; Marks, T. J. Acc. Chem. Res.2004, 37, 673-686.

Molecular Electronics

Veinot, J. G. C.; Marks, T. J. Acc. Chem. Res.2004, 38, 632-643.

Facchetti, A.; Yoon, M.; Marks, T. J. Adv. Mater.2005, 17, 1705-1725.

Facchetti, A.; Yoon, M.; Stern, C. L.; Hutchison, G. R.; Ratner, M. A.; Marks, T. J. J. Am. Chem. Soc2004, 126, 13480-13501.

Facchetti, A.; Yoon, M.; Stern, C. L.; Hutchison, G. R.; Ratner, M. A.; Marks, T. J. J. Am. Chem. Soc2004, 126, 13859-13874.

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