why nanostructured electro-optic materials?
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ROBINSON
• Use of forces to precisely position chromophores:Noncentrosymmetric ordering required.Dipole-dipole interactions oppose this ordering. Poling and Steric Forces must be used to minimize
undesired effects of dipole-dipole interactions.
• Uniform chromophore array (and high concentration) necessary:Maximizes electro-optic activity.Avoids optical loss from scattering due to density variations.
• Achieving nanostructured electro-optic materials: 1. Electric field poling of dendritic materials.2. Sequential (layer-by-layer) synthesis from an appropriate
substrate (which also serves as a cladding material). 3. Ferro-electric structures.
Why Nanostructured Electro-Optic Materials?
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Quantum Mechanics
H = E
Levels of Theory: 1st PrinciplesT
ime
Distance
femtosec
picosec
nanosec
microsec
seconds
minutes
hours
years
1 Å 1 nm 10 nm micron mm meters
Mesoscale Dynamics
Segment AveragesGroup AdditivitiesSolubilities
Molecular Dynamics
F=MA
Force Field Charges
Finite Element Analysis
Process Simulation
Equilibrium PropertiesTransport Properties
E & M Response and Properties
Engineering Design
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Theoretically inspired rational improvement of organic electro-optic materials
Theories (quantum and statistical mechanics) have guided the systematic improvement of the hyperpolarizability () of organic chromophores and the electro-optic activity of macroscopic materials.
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N NO2R
R
N NR
R
N NO2
N
R
R
SN
OO
Ph
ISX
N
R
R
S CN
NC
CF2(CF2)5CF3
N
R
R
NO
O
Ph
FCN
APTEI
N
R
R
S
NC
CN
NC
CN
TCI
N
R
R
S CN
NC
CN
N
R
R
S CN
NC
CN
TCV
N
R
R
S SO2
NC
CNTCVIP
SDS
N
R
R
SO
NCCN
NC
N
R
R
O
NCCNNC
R'
NA
DR, 30 wt%, r33 = 13 pm/V
FTC, 20 wt%, r33 = 55 pm/V
CLD
(x10-48 esu)
80
580
2,000
3,300
4,000
6,100
(x10-48 esu)
9,800
13,000
15,000
18,000
30,000
Systematic Improvement in Molecular Electro-Optic Activity: Variation of mb
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Driven by Quantum MechanicalCalculations of Molecules ThatCan Be Synthesized & Processed
Hyperpolarizability (b)
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r eff in absence of intermolecular
interactions
34
cosn
NFreff
Figure of Merit
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.
New Strategy:Gradient-Bridge, Mixed-Ligand-Acceptor Chromophores
•Quantum mechanical calculations permit the optimization of the -electron structure that defines molecular hyperpolarizability. •Microwave synthesis techniques permit dramatic enhancement in reaction yields and synthesis of new materials.
N
SS
N
N
N
HO
OH
O
D D
C
B
A
A, B, C = NO2, CN, SO2CF3, etc.
D = CF3, etc.
New Advances in Chromophore Development
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.
•Microwave synthesis has permitted dramatic enhancement in reaction yields, reducing time devoted to purification. It has also permitted many materials to be synthesized for the first time and has permitted greater flexibility in reaction conditions.
•Microwave synthesis techniques obviously permit more uniform heating of reaction mixtures. The absence of thermal gradients and “hot spots” helps minimize decomposition and side reactions. Microwave synthesis permits the use of a wider range of solvents.
•We have found this approach to be particularly effective for condensation, addition, and de-protection reactions.
Why Microwave Synthesis?
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Comparison of Microwave and Reflux Synthesis of CF3-TCF acceptor
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.
O
OH+
CN
CN
Microwave 20 W
EtONa/EtOH O
CN
NH
O
CN
NH+
CN
NO2
Microwave 20 W
EtONa/EtOHO
CN
CN
NO2
+CN
COOEt
Microwave 20 W
EtONa/EtOHO
CN
CN
COOEt
O
CN
NH+
Microwave 20 W
EtONa/EtOHO
CN
N
NO
O
S
Et
EtN
N
O
O
Et
Et
S
12
1 3
14
O
OH+
CN Microwave 20 W
EtONa/EtOH O NHN
N
+CN
CN
Microwave 20 W
EtONa/EtOH O
N
CN
CN
5 6
O
CF3
OH+
CN
CN
Microwave 20 W
EtONa/EtOH O
CN
NHF3C
+CN
CN
Microwave 20 W
EtONa/EtOHO
CN
F3C
CN
CN
78
Examples of Microwave Synthesis
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.
NBu
Bu
S O
O
CN
CN
CNF3C
, 20W, 8 min.N
Bu
Bu
S O
NCCN
CN
CF3
OTBDMS
OTBDMSEtOH
NBu
Bu
S O
O
CN
CN
CNF3C
EtOH, reflux
NBu
Bu
S O
NCCN
CN
CF31.5 hr.
NBu
Bu
O
NC
CF3
NC
CN
NBu
Bu
O+
O
CN
CN
CNF3C
cat. Py. Piper.
THF, CHCl3, reflux
NBu
Bu
O
NC
CF3
NC
CN
NBu
BuO
CN
CN
CNF3C
cat. Py. Piper.
THF, CHCl3, reflux
O
+
LMAJ 22
LMAJ 24
1
2
Coupling Reactions
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0.85 dB/cmat 1.55 mm
0.68 dB/cm at 1.3 mm
Perfluorodendron-substituted Chromophore Contributes Little to Optical Loss in Guest-Host APC Polymer
Reducing Optical Loss
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.
• Photochemical stability can be improved by chromophore design.
Lumera has demonstrated this.
• Photochemical stability can be improved by the use of scavengers
Photo Stability of Different FTC Samples
0
20
40
60
80
100
120
0 50 100 150 200
UV Exposure Time (minute)
Inte
ns
ity
Ra
tio
(%
)
FTC in Air
FTC Sealed
FTC w/ Quencher in Air
FTC w/ QuencherSealed
Optimizing Photostability
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1, 2, 3
1 32
Laser1, 2, 3
Modulates 1 Modulates 2 Modulates 3
Transmitter Receiver
1, 2, 3
1 32
1, 2, 3
1 32
Laser1, 2, 3
Modulates 1 Modulates 2 Modulates 3
Laser1, 2, 3
Modulates 1 Modulates 2 Modulates 3
Transmitter Receiver
dn
rnKv
V
BW
e
o
FWHM 233
3
Eye diagram1 Gb/s, Vpeak = 1 VDevice has ~2GHz BW
Au Electrode
SU-8
Gold ground
GND
= 2 GHz/V
Integrated WDM Transmitter Receiver
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Evolution of N<cos3>
Simple ChromophoreShape Modification
Loading
First Multi- Chromophore Dendrimer
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Centric Ordering
E
Chromophore-polingField Interaction
Thermal Randomization Chromophore-ChromophoreElectrostatic Interaction
Acentric Ordering Isotropic
<cos3>= F/5kT = f(0)Ep/5kT
<cos3> =(F/5kT)[1-L2(W/kT)]
34
cosn
NFreff
Translating Microscopic to Macroscopic Electro-Optic Activity
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Analytic Theories for Spheroidal Dipoles
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Monte Carlo Calculations
• Use Monte Carlo methods to determine the effect of dipolar interactions between chromophores.
A 5 by 5 two dimensional array
Randomly oriented dipoles
• Place dipoles on a grid (simple cubic lattice and body centered cubic lattice)
• M by M by M array with r as nearest neighbor distance.
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How Monte Carlo Works
• Choose a dipole
• Rotate dipole by: a rotation axis and angle, selected randomly
• Compare the energy before and after rotation.
If the energy is lower, keep the
move
If the energy is higher, compare Boltzmann
Probability with a [0,1] random number, and keep if
larger.
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Comparison of Potential Functions from Analytic Theory & Monte Carlo Calculations
Solid Line—Analytic Theory
2 22 2
3
Nw s s
r kT kT
.
0.3 cosexp wP A
Points—Monte Carlo Calculation
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.
Prediction of the Dependence on Poling Field
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Comparison of Theory & Experiment
.
Experiment—SolidDiamonds
2max 2 2
0.48 0.28 4.8 kT kT
N f
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Lattice Geometries
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.
New Strategy: Generalize the Concept of Dendronized Chromophores.
: Dendritic moiety
: Polymer backboneCore moiety
: NLO chromophore moiety
: Crosslinkable moiety:
x yx y
Side-Chain dendronized NLO polymer
Dendritic NLO chromophore
NLO dendrimer
Dendrimer Synthesis
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NS
S
O
NC
CN
NC
R
R
DMC3-97
NLO Chromophre
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Features of Ellipsoids• Complete flexibility of Charge and Dipole Distributions
• Complete flexibility of Connectivity to other Ellipsoids
• Complete flexibility of oreintation (for Monte Carlo and Brownian Dynamics Trajectories)
• Polarizability Tensor
• Computes all electrostatics with other Ellipsoids and arbitrary External Field
• A contact function to find Ellipsoid-Ellipsoid interactions
• Can have either Hard-Shell Repulsion or Leonard-Jones Interactions
• Solvent free energies and exposure factors (use the rolling ball method)
• Can generate dendrimers, polymers and lattices of ellipsoids
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Dendrimer Performance
Statistical Mechanical Theory explains the improved performance of dendritic chromophores.
O
O
OO
O
ON
S
CNNC
NC
NC
O
O
O O
FF
OF
O
O
FF
OF
O
N
S
NCCN
NC CNO
O
O
OF
F
O
FO
OF
F
O
FO
NS
NCCN
CN
CN
O
O
OO
F F
O F
O
O
F F
O F
O
O
O
O
By choosing a tilt
angle for the three chromophores (~60°) the experimental enhancement (of ~ 2 fold) was realized.
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Dendrimer Structure
Original Geometry
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Three-Fold Dendrimer
Three chromophores at Equilibrium
With NO poling field: Nearly Planar
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Three-Fold Dendrimer
Three chromophores at Equilibrium
With a poling field: Constrained and Aligned
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Polymer of Dendrimers
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Lattice of Dendrimers
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Thermal Annealing
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Aspect Ratio: A Search for more order
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Aspect Ratio and Field
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Mission Possible Materials (I)
• The state of the art for OEO Materials:R33: 70 pm/V (CLD in 2000) Vp: 0.8 V (2000)
R33: 130 pm/V (2002) Vp: 0.3 V (2000)
• Industry Standard: LiNiO3
R33: 32 pm/V Vp: 5 V (@40 GHz)
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Mission Possible Materials (II)
• Quantum Mechanical Based Improvements:
Increase b : Yes, by 5-10 fold
Placement of Heteroatoms; Mix Donors and Acceptors
Increase m: No, not needed Already 20 Debye and will go higher anyway
• Statistical Mechanical Based Improvements:Improve order by 5 fold (currently order is 5%)
o Design Dendrimers o Improve Steric Interactionso Place Chromophores on Polymer Backbone
Improve order 20 fold o FerroElectrically ordered materials
Only Theory can begin to crack this problem.The new R33 is 130*20 = 2600 pm/V
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Mission Possible Materials (III)
• Engineering Based Improvements:
BandWidth: Done (100+ GHz performance now)
Devices are cladding limited
Design Devices to be in Resonant Structures
(Trade Bandwidth for Vp)
Use Photonic Band-Gap Structures to obtain beam confinement and minimize the need for cladding.
(Theory can predict light beam confinement)
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Light Through Regular Array
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Light Beam in Photonic Material
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