Transcript Tobin J. Marks Department of Chemistry and The Materials

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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Published over 800
research articles and holds
80 U.S. patents.
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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
Research Activity
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Organometallics
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Photonics
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MOCVD
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Molecular Electronics
Organometallics
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Investigate the Design and Implementation
of Organometallic and Main Group
Complexes for Catalysis
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Hydroelementation: Organo-f-element
complexes for small-molecule catalysis
Olefin polymerization: Nuclearity effects in
group 4 and group 13 catalyst/cocatalyst
studies
Hydroelementation
Very desirable yet challenging atom-economical transformation.
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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
Aminoalkene/alkyne
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hydroamination/ cyclization:
Rate = k[substrate]0[Ln]1
Very sensitive to steric demands around metal center;
Proposed Hydroamination Pathway
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+ ).
Aminoallene Cyclization
Catalyst Development:
Chiral Catalysts; Enantioselective
Hydroamination
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 C1symmetric organolanthanocene
catalysts.
Other Organolanthanide Catalyzed
Hydroelementations (E = Si, B, H, P)
Molecular Electronics
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Research involves synthesis and study of thinfilm and molecular electronic materials, focusing
on the versatile thiophene-based oligomers and
polymers as semiconducting and conducting
layers.
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Utilize thin film deposition techniques like spincoating, sublimation and unique self-assembly.
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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 Electronics
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OLED/PLED
Toward the Ideal
Organic LightEmitting Diode;
nanoscale tailoring
of the anode/HTL
interfaces.
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OTFT
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Toward N-type
semiconductors
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Gate dielectrics for lowvoltage Organic Field
Effect Transistors.
Organic Light Emitting Diode
(I) Schematic of a typical
OLED heterostructure.
(II)Energy level diagram of a
typical multilayer OLED. A
and B indicate the
cathode-ETL and anodeHTL interface, respectively.
Importance of Interface
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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.
Siloxane Based SAMs: Triarylamine
Layers
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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:
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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
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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
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PLED devices: ITO/SAM
or HTL/PFO/Ca/AL
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.
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SAM modified ITO anode
enhances hole injection
current 100X times vs bare
ITO.
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Greater IP of SAM on ITO (
revealed by UPS
measurements).
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TPD-Si2 SAM moderates
discontinuity in ITO EF-PFO
HOMO.
Organic Field Effect Transistors
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The three fundamental
device components
are the contacts,
semiconductor and
the dielectric layer,
typically arranged as
shown in figure.
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Need for low voltage
operating, low cost
manufacture gate
dielectrics.
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.
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MIM and MIS leakage
and capacitance
measurements carried
out.
The current densities
for CPVP-Cn and CPSCn films lower than for
PVP and PS.
Ultrathin CPB’s exhibit
very large capacitance
values.
Self Assembled Multilayers (SAMTs)
as Dielectric Materials
Film pinhole assay by cyclic voltammetry using
bare ITO (dotted line) and nanodielectrics III
coated ITO as working electrodes (solid line).
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Measurement of nanodielectric
capacitance–voltage electrical
characteristics at 104 Hz.
The excellent insulating properties of I–III are
demonstrated by cyclic voltammetry.
Towards N-type Semiconductor:
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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
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For full realization of the potential of
organic electronics, high performance etransporting (n-type) materials needed.
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Enable applications, e.g. bipolar
transistors, p-n junction diodes and
complementary circuits.
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Varying the substitution on thiophene
backbone modulates the “band gap”.
Perfluoroalkyl substituted
oligothiophenes
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First compound: DFH-6T in
2000.
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Intensive research towards
understanding chemical,
structural and physical
properties as well as solidstate characteristics of five
homologous series of
thiophene based
compounds.
Optical properties
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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.
Electrochemistry
Electrochemistry
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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 Transistors
Field Effect Transistors
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All of the semiconductors investigated are FETactive, independent of the chemical substitution,
regiochemistry, and core dimension.
All fluorocarbonsubstituted systems functionalized
at the terminal thiophene units (1 and 2) are ntype 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.
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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:
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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:
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, 17051725.
Facchetti, A.; Yoon, M.; Stern, C. L.; Hutchison, G. R.; Ratner, M. A.;
Marks, T. J. J. Am. Chem. Soc 2004, 126, 13480-13501.
Facchetti, A.; Yoon, M.; Stern, C. L.; Hutchison, G. R.; Ratner, M. A.;
Marks, T. J. J. Am. Chem. Soc 2004, 126, 13859-13874.