speed of light

Transcript

speed of light

CAPITOLO IV°
Materiali per ottica non lineare.
Origine della Risposta ottica
nonlineare in materiali organici
molecolari. Materiali per
elettroottica. Sistemi Push-Pull e
modello della Bond Length
Alternation. Polimeri polati, vetri solgel. Multistrati auto assemblati
1
Dept.
Dept. Materials Science,
Science, Univ.
Univ. MilanoMilano-Bicocca Photonics and Biophotonics Organics Synthesis - PhoBOS
Case study 1
ORGANIC ELECTRO-OPTIC MODULATORS
or
The surface as a template for the ordered,
non centrosymmetric growth of
multilayered thin films starting from
strongly dipolar precursors
2
Dept.
Science, Univ.
3
Dept.
Science, Univ.
Critical to Next Generation Computing
•High frequency, ultra high stability
clocks
•On-chip signal distribution
•Chip-to-chip interconnection
•Module-to-module interconnection
- Potential for Lower Cost
- Exceptional Large Bandwidth, Low
Relative Permittivity
- Mechanical Properties
- Integration with Semiconductor
Electronic (Very Large Scale
Integration -VLSI)
- Potential for Lower Operating
Voltages
4
Dept.
Science, Univ.
Electro-Optic Materials: the need
for manipulation of optical signals
LiNO3: 10GHz, 35dB
Vπ = 5-6 V
Mach-ZehnderModulator
5
Dept.
Science, Univ.
Electro-Optics: The Phenomenon
• An electro-optic material (device) permits electrical and optical
signals to “talk” to each other through an “easily perturbed”
electron distribution in the material. A low frequency (DC to 200
GHz) electric field (e.g., a television [analog] or computer [digital]
signal) is used to perturb the electron distribution (e.g., π-electrons
of an organic chromophore) and that perturbation alters the speed
of light passing through the material as the electric field
component of light interacts with the perturbed charge distribution.
• Because the speed of light is altered by the application of a control
voltage, electro-optic materials can be described as materials with
a voltage-controlled index of refraction.
Index of refraction = speed of light in vacuum/speed of light in material
6
Dept.
Science, Univ.
Nonlinear Optical Transmission
400 nm
400 nm
800 nm
800 nm
1064 nm
532 nm
1064 nm
355 nm
R2N
NO2
λmax = 430 nm (CHCl3)
NO absorption
7
Dept.
Science, Univ.
8
Dept.
Science, Univ.
9
Dept.
Science, Univ.
N
ZWITTERIONI
N
C
C
O
N
C
S
O
N
N
N
S
C
N
N
BETAINE
MEROCIANINA
O
NH3
N
CH3
CH2
COO
10
Dept.
Science, Univ.
11
Dept.
Science, Univ.
When and How Nonlinear Optics (NLO)?
Nonlinear optical phenomena arise when applied external fields, ie,
either light or low frequency electrical fields, are sufficiently strong
to compete with internal electrostatic interactions. Thus, nonlinear
optical materials are typically those containing weakly bound (highly
polarizable) electrons (read: π-electrons).
electronic excited state (LUMO)
ω
ω
2ω
400
nm
1064
nm
ω
ω
ω
ω
3ω
ω
ω
800
nm
electronic ground state (HOMO)
Linear
Absorption
(Lambert-Beer)
Second-Harmonic
Generation (SHG)
(II order NLO)
Third-Harmonic
Generation (THG)
(III order NLO)
Two-Photon
Absorption (2-PA)
(III order NLO)
12
Dept.
Science, Univ.
Molecular design guidelines:
the Two State Model
Approximations:
1. Almost one dimensional (linear) molecules
2. Main charge-transfer transition aligned with conjugation axis
3. Only the ground and excited states are taken into account
β∝
µ ∆µ
2
eg
E
2
eg
LUMO (e state)
Eeg
HOMO (g state)
µeg = transition moment between ground and excited states (proportional to
the extinction coefficient ε)
∆µ = dipole moment difference between ground and excited states
Eeg = HOMO-LUMO transition (from the absorption spectrum)
13
Dept.
Science, Univ.
Jablonski Energy Diagrams
Sn
photochemistry
and
photophysics
thermal relaxation
S1
ISC
ns-µs
T1
2-PA
fluor
phos
fs
ps-ns
µs-ms
S0
14
Dept.
Science, Univ.
The Mach Zehnder Interferometer
Vπ = λd/(2n3r33LΓ
Γ)
Vπ is the voltage required to
achieve signal transduction (on/off
modulation)
λ = optical wavelength
n = index of refraction
r33 = electro-optic coefficient
L = interaction length
Γ = modal overlap integral
d = electrode gap
From M G Kuzyk, C W Dirk, Marcel Dekker Inc., 1998
15
Dept.
Science, Univ.
Why Organic Electro-Optic Materials?
Intrinsic material bandwidths of several hundred gigahertz. The
response time (phase relaxation time) of π-electrons in organic materials
to electric field perturbation is on the order of femtoseconds. Operational
bandwidths of 150 GHz have been demonstrated for modulators &
switches
• Organic electro-optic coefficients are currently 2-4 times higher
than lithium niobate and getting larger
• Organic EO materials are highly processable into 3-D circuits and
can be easily integrated with semiconductor electronics and silica
fiber optics
16
Dept.
Science, Univ.
Comparison of Lithium Niobate and Polymer
Electro-Optic Modulators
State-of-the-art High Speed Infrared Modulators
Commercial Lithium Niobate Devices—The Competition
Vπ: 6 V @1550 nm, 30 GHz Bandwidth, $6000/per unit
Commercially Available Polymer Devices
Vπ: 1.2 V @ 1300 nm, 1.8 V @1550 nm
20 GHz and 30 GHz Bandwidth (3dBe)
Published Prototype Device Results
Vπ: 0.77 V @ 1300 nm
100 GHz operation
10 Modulator Chips on 3 Inch Wafer
Pacific Wave Industries,
California 90245
2 Push-Pull MZ Modulators on One Chip
17
Dept.
Science, Univ.
NONLINEAR OPTICAL EFFECTS: Microscopic and
Macroscopic Polarization—Power Series Expansion
The molecular polarization P for a given molecule in the presence of a field E can
be wtritten as:
pi = α ij E j + β
ijk
Ek E j + γ ijkl E j Ek El + ...
β is the first nonlinear term, known as molecular first hyperpolarizability. For a
symmetric molecule even order terms, β and higher, are zero.
For a bulk material or a film:
Pi = χ ij E j + χ (2)ijk E k E j + χ (3)ijkl E j E k E l + ...
χ(2)represents the material first nonlinear susceptibility. The chromophores
must be aligned acentrically within the material to realize a nonzero χ(2). The
electro-optic effect is a second order nonlinear optical phenomenon.
GEOMETRIC PREREQUISITE (β
β, χ ≠ 0) => NO CENTROSYMMETRIC STRUCTURE
18
Dept.
Science, Univ.
The electro-optic coefficient r33
The coefficient of the second term in the power series expansion
of material Polarization in terms of the applied electric fields, χ(2),
is given by:
χ ( 2 ) zzz = Nβ zzz < cos3 θ > (const )
r33 = −2 χ (2)zzz /(n z ) 4
r33 = βN<cos3θ>(constant)
Loading Parameter = N <cos3θ> = (r33/β) (constant)
r33 = electro-optic coefficient
N = chromophore number density (molecules/cc)
b = molecular first hyperpolarizability
N<cos3q> = acentric order parameter
n = refraction index
*The constant depends on the dielectric properties of the
material lattice
19
Dept.
Science, Univ.
Chromophore Requirements
•Large hyperpolarizability and large dipole moment
optimization of β
•No absorption at operating wavelength
•Stability
--Thermal
--Chemical & Electrochemical
--Photochemical
•Solubility
•Compatibility with materials processing (polymeric,
glassy…)
Electro-optic activity requires noncentrosymmetric
chromophore symmetry, i.e., <cos3q> must be large
•Requires optimization of N<cos3q>
20
Dept.
Science, Univ.
Traditional Chromophore Design:
Push-Pull derivatives
NC
Electron
Donor
N
S
NC
CN
S
O
Electron
Acceptor
π-conjugated bridge
β∝
µ eg2 ∆µ
E
2
eg
Strong charge transfer transition from an electron
donor group to an electron acceptor group
Strongly dipolar structures (dipole moment inversion on
going from the ground to the excited state)
Highly polarizable π conjugated bridge
21
Dept.
Science, Univ.
Traditional Chromophore
Design: Push-Pull derivatives
µβ enhancement tools:
1. Use of stronger Donor and Acceptor Groups
2. Introduction of more polarizable π-bridge (tuning
of the bridge aromaticity, heterocycles)
3.Conjugation length increase
still preserving solubility, stability, processability and possibly
easy synthetic access
Zhang and Jen Proc. SPIE 372 (1997)
Ermer et al. Chem Mater. , 1498 (1997).
22
Dept.
Science, Univ.
Push-Pull derivatives - Acceptors
∗ NO2
∗
NO2
CN
∗
CN
∗
∗
N
∗
S
Ph
O
N
∗
O
O
Me
N
Me
O
F
F
NC
NC
CN
CN
Dalton acceptor
∗
O
F
CN
CN
CN
F
∗
CN
H
O
F
NC
NC
S
∗
O
NC
CN
Sandoz acceptor
∗
R
N
N
∗
∗
NO2
X
X = S, NR, O
(CO)5M ∗
M N
∗
N
N
M
N
23
Dept.
Science, Univ.
Push-Pull derivatives – π-bridges
∗
∗
∗
∗
∗
n
n
∗
∗
∗
∗
∗
n
∗
N
∗
N
∗
N
∗
∗
∗
S
∗
∗
S
S
∗
X
∗
Y
X = O, S; Y = N
24
Dept.
Science, Univ.
Push-Pull derivatives - Donors
OR'
R
R
N
N
R'O
∗
R'O
∗
R = Me, Et, Bu, Ph
S
∗
∗
∗
R' = H, Ac, TBDMS
NC
NC
R 2N
N
N
N
Me
∗
NC
S
∗
∗
NC
∗
O
25
Dept.
Science, Univ.
Target for electro-optics applications
Figure of Merit: electro-optic coefficient r33
(Mach-Zender Modulator: info-coding in fiber-optic transmission)
Present technology
LiNbO3
r33 = 31 pm V-1
Best performing poled organic NLO polymer to date
(Bu)2N
NC
CN
polycarbonate matrix
O S
O
r33 = 55 pm V-1
20% wt% loading
26
Dept.
Science, Univ.
Design motifs for obtaining EO-materials with no
centrosymmetric superstructure from NLO-fores
POLING
PROCESS (to
iso-orient the
Chromophores)
IS NECESSARY
NO
POLING
27
Dept.
Science, Univ.
Incorporation Of NLO-phoric Molecules Into Solids
There exist four major methods by which chromophores are
incorporated into polymers. In the main-chain approach,
chromophores are chemically attached to the polymer backbone
itself. In the side-chain approach, chromophores are chemically
attached as part of the side chain to the polymer backbone. These
systems have the advantage that a high concentration for the
chromophores can be obtained without crystallization, phase
separation, or the formation of concentration gradients. In the
cross-linking approach, chromophores act as crosslinking bridges
between two polymer chains. This method effectively destroys the
mobilization of segments of the polymer chains. And since polar or
octopolar alignment of the dipole moments is required, most of the
cross-linking must occur during or after the poling process is
completed. In the guest-host system approach, chromophores form
a solid solution in a polymer host. This approach has the simplicity
that the chromophores do not need to be chemically bound to the
polymer.
28
Dept.
Science, Univ.
For each of the four approaches mentioned, a poled polymer system
in
the
absence
of
an
applied
static
electric
field
is
not
in
thermodynamic equilibrium. The order parameter (cos(Φ
Φ)), where Φ is
the angle between the dipole moment of a molecule and the poling
field, therefore decays over time, resulting in the decay of the
macroscopic second order susceptibility. One can greatly reduce this
intrinsic thermal relaxation by using polymer systems with intrinsically
high glass transition temperatures. One elegant example currently
under development is the class of optical polyimides with glass
transition temperatures greater than 300-400°C.
29
Dept.
Science, Univ.
INCORPORATION OF 2nd and 3rd order NLOPHORES INTO MATRICES
Matrix
•HOST-GUEST
advantage
drawbacks
high solubility
short-lived stability
high poling temperature
SIDE CHAINS
long-lived stability may be less compatible
OF BACKBONE
2nd order are highly
polar, even
zwitterionic systems
and thus salt-like!
Many 3rd order are salts !
high poling temperature
How to make salts
compatible
with polymers ?
30
Dept.
Science, Univ.
HIGH Tg POLYMERIC MATERIALS FOR NLO
ADVANTAGES
DRAWBACKS
- good mechanical properties
- hard reaction conditions
- high thermal and chemical stability - low processability
- temporal stability of performances - toxicity of employed
- good optical quality
solvents
Requirement
high concentration of efficiently active chromophores
BUT…
The highest the activity,
the lowest stability and solubility!!!
31
Dept.
Science, Univ.
CROSSLINKED POLY(AMIDO)AMINES
O
a
O
N
N
O
CH3
b HN
NH
+
d R-NH2
Water
4 d, r.t.
O
N
N
O
H2N
NH2
N
N
O
N
N
R
N
c
O
Cross linking agent
N
N
O
N
O
N
O
Functionalized chromophore
- extraordinary mild reaction conditions
- easy tunability of mechanical properties
- easy processability
- good optical properties
- concentration of the active molecule from 0.05 to 40 % by weight
independently on the solubility (heterogeneous phase reaction)
PROTECTION FROM PHOTODEGRADATION 32
Dept.
Science, Univ.
FUNCTIONALIZED MOLECULAR PRECURSORS
H2N
CH3
N
H
N
H2N
N
CH3
N
N
O
Br
H2N
O
Br
N
CN
S
CN
H2N
H
N
O
O
N
CN
S
CN
- Presence of a primary amino group is the only requirement
- The nature of substituents on the pyridic nitrogen does
not influence the electronic structure
33
Dept.
Science, Univ.
PHOTOSTABILITY – THE MATRIX EFFECT
H3C
N
CN
S
0%
50%
CN
MeOH
(after 48 h)
acetone
(after 4 h)
Poor solution photostability because of reaction with singlet oxygen: suicidal chromophore
Tertiary amino groups are efficient scavengers for 1O2
Solid state photobleaching
0h
2h
10 h
40 h
80 h
120 h
180 h
240 h
300 h
400 h
800 h
1000 h
1200 h
O
CH3
O
N
N
N
N
n
Dramatically enhanced photostability in the solid!
34
Dept.
Science, Univ.
COME SI MISURA L’IPERPOLARIZZABILITA’
QUADRATICA MOLECOLARE β?
TECNICA EFISH (Electric Field Induced Second
Harmonic Generation)
TECNICA SOLVATOCROMICA
TECNICA HRS (Hyper Raleigh Scattering)
Per i materiali bulk in polvere, l’efficienza di seconda armonica viene
determinato mediante la
TECNICA SPERIMENTALE DI KURTZ-PERRY
Per i film può essere misurata con il metodo delle frange di
Maker (coefficienti d ∝ χ (2))
35
Dept.
Science, Univ.
TECNICA EFISH
Le molecole NLO attive in una soluzione vengono orientate mediante l’applicazione di un
forte campo elettrostatico L’iperpolarizzabilità quadratica viene ottenuta dalle frange di
interferenza di Maker. Fornisce la proiezione della componente vettoriale di β lungo la
direzione del momento di dipolo µ.
ω
3+
laser Nd :YAG
1064 o 1907 nm
β≠ 0
soluzione
SHG
2ω
frange di Maker
I 2ω , l c → γ EFISH → βλ
Campo elettrico applicato
(5 -8 kV )
Contributo dipolare
Contributo elettronico
γ EFISH =
µβλ
5 KT
+ γ 0 ( − 2ω ;ω, ω , 0 )
Intens
ità
della
2a
armon
ica
Traslazione della cella (mm)
36
Dept.
Science, Univ.
IlIl metodo
metodo solvatocromico
solvatocromico
Fornisce il valore di β lungo la direzione
di trasferimento di carica.
Spostamento della banda di assorb. o
emissione in solventi di diversa polarità
Assorbimento
Equazione di McRae:
(
(
)
 ε −1 n2 −1 
2 n2 −1

ν a =ν + A 3 2
+ B
− 2
ε
+
2
a 2n + 1
n
+
2


g
a
B=
)
Emissione
− 2 µ g (µ e − µ g )
ν a reg2 ∆µeg
3
= 2 2 2 2 2
2h c ν a −ν1 ν a − 4ν12
2
βCT
(
)(
)
νa = frequenza della banda di
assorbimento MLCT ; ν1= frequenza
della radiazione incidente (1.907 nm);
reg =momento di dipolo della
transizione (reg2=2.13 x 10-30 f/na ,
(µ
µe- µg) = ∆ µ eg = variazione del
momento di dipolo tra stato eccitato
e fondamentale
Equazione di Liptay
hca 3
↓
∆µeg noti µg e a
 3M
a = 
 4πdN AV



 ε −1 n2 −1 

− 2
ε
+
2
n
+
2


ν a −ν e = C + D
1/ 3
M
Vm = 4 / 3πa =
dN AV
3
2(µ e − µ g )
2
D=
hca3
S.Bruni, E.Cariati et al. Spectrochimica Acta Part A , 2001, 57, 1417
37
Dept.
Science, Univ.
MISURA
° ORDINE
MISURA DELLE
DELLE PROPRIETA
PROPRIETA’’ NLO
NLO DI
DI II
II°
ORDINE
EFISH
βλ
Proiezione lungo l’asse del momento di dipolo
Misura di β
SOLVATOCROMISMO
Confronto possibile solo se la
direzione del trasferimento di
carica coincide con la
direzione del momento di
dipolo
βCT
Componente lungo l’asse del trasferimento di carica
38
Dept.
Science, Univ.
Hyper Rayleigh Scattering (HRS)
Per molecole dipolari,ottupolari (µg=0), neutre o ioniche.
Fornisce una media sulle varie orientazioni di tutte le
componenti del tensore β
ω
Nd3+ : YAG laser
1064 or 1907 nm
β≠ 0
soluzione
SHG
2ω
Scattered signal
at 90°
I2ω
< β2>
β = β J =1 + βJ =3
βJ = 1 : componente dipolare o vettoriale del tensore β
βJ = 3 : componente ottupolare del tensore β
39
Dept.
Science, Univ.
HRS
NPP=N-4-nitrofenilprolinolo polvere
PM = fotomoltiplicatore, C= cuvetta portacampione, L= lenti
convergenti, FV = filtri, P = polarizzatore
40
Dept.
Science, Univ.
IL METODO KURTZ-PERRY
ω
laser Nd3+:YAG
1064 o 1907 nm
Nd 3+ : YAG
LASER
1.06 µm
χ(2) ≠ 0
campione (polvere)
SHG
2ω
dove I2ωω ∝ χ(2)
Raman Cell
Filled with H2
1.91 µm
Le misure SHG sono fatte rispetto a uno standard (quarzo, urea).
41
Dept.
Science, Univ.
Systematic Improvement of µβ
Increase in the accepting strength
Increase in the conjugation length
µβ (x10 -48 esu)
R
N
80
N O2
R
µβ (x10 -48 esu)
R
N
NA
NC
S
R
9,800
CN
CN
R
N
580
N
R
N
N O2
TC V
R
N
DR , 30 w t% , r 33 = 13 pm /V
R
O
N
S
O
CN
T C VI P
2,000
Ph
R
CN
R
15,000
NC
ISX
N
S
R
S
CN
R
SO2
R
NC
N
CN
N
S
13,000
NC
R
3,300
C F2 (C F2 ) 5 C F3
SDS
R
FC N
NC
CN
N
R
NC
S
18,000
O
R
N
4,000
R
O
Ph
AP TE I
N
F T C , 20 w t% , r 33 = 55 pm /V
R
N
O
R
CN
R'
R
N
S
R
TC I
CN
NC
6,100
CLD
30,000
O
NC
NC
CN
NC
42
Dept.
Science, Univ.
The bond length alternation model
For a given π-bridge there is an optimal combination of Donor and Acceptor
groups. If the ground state charge distribution is too asymmetric the β value
decreases. Marder, S. R.; Kippelen, B.; Jen, A. K.-Y.; Peyghammbarian, N. Nature (London)
1997, 388(6645), 845-851.
A
D
Neutral structure
β>0
A
D
+
Cyanine limit
β=0
β
Zwitterionic structure
β<0
0
-
0.04
BLA
BLA = average length difference between double and single bonds in the gr- state
At the cyanine limit the molecule is symmetric and the β is accordingly zero.
43
Dept.
Science, Univ.
Further Molecular Descriptors
MIX = - cos θ = -
[
(
V
V + 4t
2
2
ag
)
2 −1/ 2
c =1/ 21− ∆µ 4µ + ∆µ
2
2
]
BLA (in Å) = 0.11 MIX
C2 is a measure of the intramolecular charge transfer !!
44
Dept.
Science, Univ.
The bond length alternation model
Me2N
O
Me2N
Me2N
Me2N
O
O
Me2N
O
NMe2
Me2N
NMe2
Me N
O
Me N
O
( β > 0)
( β = 0)
( β < 0)
45
Dept.
Science, Univ.
A figure of merit:
hyperpolarizability per unit of MW
MW
βµ(0)
βµ / M
567
14920
26.3
265
6990
26.4
347
11000
31.7
O
N
N
O
N
S
Marder, Science, 1994
Me
N
CN
S
Me
CN
N
S
S
CN
CN
Gazz. Chim. Ital. 1997, 127, 165; J. Org. Chem. 1997, 62, 5755; Mat. Res. Soc. Symp. Proc. 1998, 488, 819
46
Dept.
Science, Univ.
Probing the contribution of the two limit forms:
single/double-bond character of the central unit
Experimental Evidence: Coupling Constants (J/Hz)
R
aromatic
H
N
CN
S
R
H
N
CN
S
CN
quinoid
CN
H
H
quinoid
Solvent
Pyridine
Quinoline
Acridine
Dioxane
13.61
12.99
12.69
Chloroform
14.02
13.42
12.78
DMF
15.10
14.33
13.76
aromatic
Abbotto, A.; Beverina, L.; Bradamante, S.; Facchetti, A.; Klein, C.; Pagani, G. A.; Redi-Abshiro, M.; Wortmann, R. Chem. Eur. J. 2003, 9(9), 1991-2007.
47
Dept.
Science, Univ.
TUNING FIRST HYPERPOLARIZABILITY THROUGH RING
FUSION AND SOLVENT POLARITY
48
Dept.
Science, Univ.
TUNING FIRST HYPERPOLARIZABILITY
THROUGH RING FUSION AND SOLVENT POLARITY
R
N
CN
S
R
N
CN
S
CN
CN
Experimental (computed) β0µ values (10-48 esu)
Solvent
Pyridine
Quinoline
Acridine
Gas phase
(+310)
(+370)
(+420)
Dioxane a
-510 (-800)
+ 610 (+750)
+ 1880 (+1760)
Chloroform b
- 6990 (-9600)
(-10900)
(-13500)
DMF b
- 2000 (-4200)
(-3900)
(-3600)
a
Electrooptical Absorption Measurements (R. Wortmann) b EFISH data (P. Prasad, J. Zyss)
Abbotto, A.; Beverina, L.; Bradamante, S.; Facchetti, A.; Klein, C.; Pagani, G. A.; Redi-Abshiro, M.; Wortmann, R. Chem. Eur. J. 2003, 9(9), 1991-2007.
49
Dept.
Science, Univ.
Computed Solvent-dependent Charge Distribution
Me
Me
acceptor
acceptor
N
N
CN
CN
S
S
CN
CN
donor
donor
1.000
1.000
0.800
0.800
acceptor
Natural Charge
0.600
0.600
0.400
0.400
0.200
0.200
C=C
0.000
0.000
-0.200
-0.200
-0.400
-0.400
Py
1c
Qu
2c
Ac
3c
-0.600
-0.600
-0.800
-0.800
donor
Neutral-quinoid
S
DM O
SO
D
M
F
F
DM
D
M
e
ac
et
on
e
ac
e
to
n
m
CH
Cl
3
of
or
or
ty
l
et
di
he
bu
r
ty
le
t
ch her
l
bu
di ane
ox
an
e
du
di
ox
ga
s
ga
s
ph
as
ph
as
e
e
-1.000
-1.000
Zwitterionic - aromatic
50
Dept.
Science, Univ.
Electrooptical Absorption Measurements
in Dioxane and Derived NLO properties
Pyridyl
Compound
Quinolyl
Acridyl
µg
(10−30 C m)
51.2
46.3
30.1
µe
(10−30 C m)
41.4
52.0
73.1
∆µ
(10−30 C m)
- 9.8
5.7
43.0
β0
(10-50CV-2 m3)
- 79
56
310
0.56
0.46
0.22
c2
C2 is a measure of the intramolecular charge transfer !!
51
Dept.
Science, Univ.
Solvato- and Solidochromic Data for the N-decyl
Pyridyl Chromophore in Selected Film Matrixes.
Entry
Matrix
ε
λmax (nm)
1
Siliceous (SiO2 sol-gel)
>6
592
2
Poly(p-hydroxy styrene)
?
616
3
Poly(ethylene glycol)
3.6-4.0
628
4
N-Decyl Pyridyl (neat)
?
648
5
PMMA
3.2-3.5
676
6
Polymaleimide
3.1-3.3
680
7
Poly(vinylbenzyl chloride)
2.7-2.9
702
8
Polystyrene
2.5-2.6
724
52
Dept.
Science, Univ.
Issues with Traditional 1D Chromophores
D
π-bridge
A
Increasing in conjugation length is usually accompanied by:
optical absorption red shift (eroding transparency)
reduced thermal stability
Challenge is clear:
How can we optimize EO response, thermally stability
and transparency?
53
Dept.
Science, Univ.
Design of Twisted Chromophores
R
R
R
R
THEORY
N
O
θ
N
O
θ
R
R
Twisted "Zwitterionic" Structure
R
R
Flat "Quiniod" Structure
I. Characteristics:
-Sterically-enforced reduction in D-π
π-A
conjugation
- Charge-separated zwitterionic ground state
- Large Δµge
- Tune β and λ with θ
II. Attractions:
- chromophores “Simple” molecules
- µβ
β figures ~ up to 10 × greater than other
reported
III. Challenge
- Synthesis
θ ≈ 70 - 85°°
Albert, I. D. L.; et al. JACS, 1997, 119, 3155.; Albert, I. D. L.; et al. JACS, 1998, 120,
11174.: Keinan, S.; et. al. THEOCHEM, 2003, 633(2-3), 227
54
Dept.
Science, Univ.
The twisted Chromophores
t-Bu
O
n
t-Bu
R N
TM
TM-1, n = 0, R = Me
TM-2, n = 1, R = n-Octyl
CN
R N
n CN
TMC
TMC-1, n = 0, R = Me
TMC-2, n = 0, R =
TMC-3, n = 1, R =
Kang, Facchetti, Peiwang, Ho, Marks, Righetto, Cariati, Ugo Angew. Chem.
Int. Ed. 2005, 44(48), 7922-7925.
55
Dept.
Science, Univ.
Synthesis
O N
O
Br
B(OH)2
NaH2PO2
O N
O
N
N
N
OTf
I
NaCH(CN) 2
Pd(PPh 3)4
NH=CPh 2
Pd(OAc)2/BINAP
Cs2CO3
N
N
O
OH
Pd/C
Pd2(dba)3/ligand
K3PO4
Tf2O
Pyridine/HCl
Ph
N
CN
N
i. ROTf
CN ii. MeONa
Ph
NaOAc
NH2OHHCl
N
NH2
i. NO+BF4ii. NaI
1, R = Me
2, R =
CN
CN
N
Pd(OAc)2/PPh3, NEt3
CN
i. ROTf
CN ii. MeONa
3, R =
Kang, Hu; Facchetti, Antonio; Stern, Charlotte L.; Rheingold, Arnold L.; Kassel, W. Scott; Marks,
Tobin J. Org. Lett. 2005, 7(17), 3721-3724.
56
Dept.
Science, Univ.
X-Ray Diffraction Characterization
CN
N
CN
1
θ = interplanar twist angle
Highly twisted θ = 80-85°°− Pronounced reduction in inter-ring π-conjugation - Predominant negative charge localization in C(CN)2 group.
Significant aromatic character in pyridinium ring - A stable, highly
charge-separated zwitterionic geometry dominates the ground state
57
Dept.
Science, Univ.
NLO Response Properties. µβ
Chromophore Figure of Merit: µβ/Mw
EFISH µβ (10-48 esu)
CN
1000
N
CN
900.8
N
CN
CN
t-Bu
O
t-Bu
- 315,000 (±
±12%)
CN
N
CN
µβ/Mw at 1907 nm (10-48esu)
N
- 24,000 (±
±18%)
N
CN
CN
800
t-BuMe2SiO
N
t-BuMe2SiO
O
CN
CN CN
AcO
600
NC
N
S
CN
CN
O
AcO
Bu
Bu
N
NC
S
CN
CN
400
Bu
N
NC
Bu
CN
S
CN
N
CN
CN
200
NC
Me2N
0
S
N
N
2.1
NO2
17.3
25.5
27.1
25.9
45.7
57.8
- 466,000 (±
±8%)
58
Dept.
Science, Univ.
The electro-optic coefficient r33
The coefficient of the second term in the power series expansion of
material Polarization in terms of the applied electric fields, χ(2), the
susceptability is given by:
χ ( 2 ) zzz = Nβ zzz < cos3 θ > (const )
r33 = −2 χ (2)zzz /(n z ) 4
Pi = α ij E j + β ijk Ek E j + γ ijkl E j Ek El + ...
Loading Parameter = N <cos3θ> = (r33/β
β) (constant)
r33 = electro-optic coefficient - N = chromophore number density (molecules/cc)
β= molecular first hyperpolarizability - N<cos3q> = acentric order parameter
n = refraction index
*The constant depends on the dielectric properties of the material lattice
59
Dept.
Science, Univ.
Optimization of Electro-Optic Activity
Molecular Level
Requires optimization of β
Molecular design is the key
Macroscopic Level
•Electro-optic activity requires noncentrosymmetric
chromophore symmetry, i.e., <cos3θ> must be large
•Requires optimization of N<cos3θ>
60
Dept.
Science, Univ.
Design Motifs For Acentric Electrooptic Organic Materials
Poled HostHost-Guest
POLING
PROCESS
(to iso-orient the
Chromophores)
Poled and Functionalized
Poled ,Functionalized , inked
Crosslinked
Poled ,Crosslinkable Matrix
IS NECESSARY
Chromophoric LB
LBFilm
Film
SelfAssembled Superlattice
Superlatt (SAS)
Self -Assembled
NO POLING
= Chromophore Module
61
Dept.
Science, Univ.
Poled polymers
Strongly Dipolar Chromophore
Random Host Guest
polymer
T < polymer Tg
DC field off
χ2 = 0 pm/V
T > polymer Tg
DC field (strong) on
χ2 ≠ 0 pm/V
Rapid cooling
T << polymer Tg
DC field off
χ2 ≠ 0 pm/V
Poor temporal stability
62
Dept.
Science, Univ.
Corona poling experimental setup
The Charge Deposition on the polymer surface allows for the minimum
possible separation between the electrodes (higher DC fields)
Oxygen contamination must be avoided (ozone formation)
63
Dept.
Science, Univ.
Electro-optic polymeric materials poling process
A DC poling field is applied across the chromophore / host matrix.
E
F
i
e
l
d
Top electrode
CN
CN
O
NC
CF 3
NC
O
NC
CF 3
NC
CN
CF 3
NC
O
O
O
NC
CF 3
CF 3
NC
CN
NC
O
NC
CN
NC
CF 3
NC
CN
CF 3
NC
O
NC
CN
NC
O
NC
CN
CF 3
NC
N
OTBDMS
N
N
OTBDMS
TBDMSO
OTBDMS
TBDMSO
N
TBDMSO
OTBDMS
N
N
TBDMSO
OTBDMS
OTBDMS
TBDMSO
TBDMSO
N
N
OTBDMS
OTBDMS
TBDMSO
TBDMSO
Bottom electrode
Ideal case (no intermolecular interactions) : < cos3 θ> = µE / 5kT
64
Dept.
Science, Univ.
SiO2
65
Dept.
Science, Univ.
=
?
I ciclooligosilossanolati di formula generale [RSi(O)O]nn- (R = Ph; n = 3,
4, 6…) possono rappresentare un modello di un monostrato di cromofori
organici legati ad una superficie a base silicea.*
-
-
O R
Si
O
O
R Si O Si OR
O
-
-
R
O
O
O
O Si O Si R
R Si O Si OR
O
O R
R Si O Si OO R
O O
Si
Si
R O
O O
O Si O Si R
R -O
* Pozdniakova, Yu. A.; Lyssenko, K. A.; Korlyukov, A. A.; Blagodatskikh, I. V.; Auner, N.;
Katsoulis, D.;
Shchegolikina, O. I. Eur. J. Inorg. Chem. 2004, 1253-1261
66
Dept.
Science, Univ.
Sintesi di anelli ciclotetrasilossanici
Formula generale:
[4-X-C6H4Si(O)OR]4 (R=Na, SiMe3 X = Cl, Br, CH2Cl, CH=CH2).
X
X
X
X
EtO Si OEt
OEt
X
X
X
Me3SiCl, pyridine
NaOH, H2O
EtOH, r.t.
X
X
O Si
OSi
O
O
O
Si
O
4 Na
Si O
O
resa 40-80%
X = Cl, Br, CH=CH2, CH2Cl
M. Ronchi, M. Pizzotti, A. Orbelli Biroli, P. Macchi, E. Lucenti,
C. Zucchi,
J. Organom. Chem., 2007, 692, 1788-1798
n-hexane, ∆
- NaCl
O Si
Si OSi
Si O
O
O
Si
O
Si O Si
O Si
resa 40-70%
- solubilità in solventi organici
- stabilità del legame Si-O-Si
67
Dept.
Science, Univ.
Modelli cromoforici NLO attivi
N
I
I
I
O Si
Si OSi
Si O
O
Si
O
Pd(PPh3)2Cl2, CuI
+4
Et3N, THF, ∆
SiO Si
O Si
yield: 47%
H
1) tBuLi, Et2O, -78°C
Br
O Si
Si OSi
Si O
Br
O
O
O Si
Si OSi
Si O
2) I2, Et2O, -78°C
Br
N
N
N
I
O
N
Si
O
O
Si
O
SiO Si
O Si
Br
O
Si O Si
O Si
68
Dept.
Science, Univ.
Effetti cooperativi: cromofori non indipendenti
µβEFISH × 10-48 (esu)
(1.91 µm)
composto
N
N
(solvente CHCl3)
N
N
Si O Si
Si O
O
µ (D)
β × 10-30
(esu)
68
3.08
22
318
3.64
87
238
3.96
60
(solvente CHCl3)
9.00
22
O
Si
Si O Si
O Si
O
composto
µβEFISH × 10-48 (esu)
(1.91 µm)
N
198
O Si
µ (D)
β × 10-30
(esu)
Si O Si O Si
O
Si
N
N
N
N
N
839
O
Si
Si O Si
Si O
O
O
Si
10.53
80
O
Si O Si
O Si
Si O Si O Si
O
Si
N
N
N
N
N
780
O Si
Si O Si
Si O
O
O
Si
11.30
69
O
Si O Si
O Si
Si O Si O Si
O
Si
69
Dept.
Science, Univ.
Self Assembled Acentric Multilayers Sinthesys
70
Dept.
Science, Univ.
i
=>
ii
=>
iii
=>
i) Deposizione; ii) Rotazione rapida; iii) Riscaldamento
Materials construction via Layer-by-layer siloxane self-assembly
Condensation
Chemistry
Si O H
+
Cl
Si OH
+
OH Si
Si
Si
O
Si
Si
O
Si
Marks,T.J.Acc. Chem. Res. 1996, 29, 197-202; Marks,T.J.,Ratner,M.Angew.Chem.Int.Ed.Engl.1995,34, 155-173.
71
Organized self assembled monolayers
with Zwitterionic Chromophores
I
I
I
I
CN
S
OH
OH
OH
N
GLASS, QUARZ, SILICON
SiX3
Si O
Si O
Si O
O
O
O
O
O
O
IN SOLUTION
∆
X = Cl, I, OR
UV-Vis
1
Na
CN
NC
NC
CN
0.9
S
S
NC
CN
CN
S
0.8
Absorbance
0.7
0.6
0.5
N
N
0.4
N
0.3
0.2
0.1
0
300
400
500
600
Wavelength (nm)
700
800
O
Si O
O
O
Si O
O
O
Si O
O
Facchetti, A. ; van der Boom, M. E.; Abbotto, A. ; Beverina, L.; Marks, T. J.; Pagani, G. A. Langmuir 2001, 17, 5939-5942.
72
Dept.
Science, Univ.
73
Dept.
Science, Univ.
NLO characterization
100
SHG Response
80
χ(2)zzz ~5.0 × 10-8 esu (~20 pm/V)
60
40
• bleaching effect
• depolarization due to
chromophore-chromophore
interactions
20
0
0
10
20
30
40
50
60
70
Angle of Incidence
Zwitterionic chromophores may be problematic
for this approach
74
Dept.
Science, Univ.
Self-limiting chemisorptive siloxane self assembly
HO
OH
Silica, glass-like reactivity
Reactive
Functionalities
I
N
O
N
N
OH
OH
OH
O
O
O
Si
O
O
Si
Si
Si
O
O
OO
O
Si O
O
Si O Si O
Si
O
O
O
O O
O
O
O Si
Si
Si O
Si
O
O O
O
HO
OH
Me
I
Si
I
Cl
HO
PEPOH
HO
HO
PEPOH
Me
N
Me
N
N
OH
HO
N
N
Me
HO
Cl ClCl
Si
O
Cl
Si Cl
O
Si
Cl ClCl
Si
O
O
O
O
Si
Si
O
OH
N
N
N
Me
Me
I
I
N
I
I
N
N
I
I
N
I
O
Si O
Si O Si O
O O O O O
O
Si O
O
O
Si O
O
O
Si O
O
O
Si O
O
O
N
N
I
I
Si O
O
Me
N
N
O
N
N
Si O
O
SA-PEPOH
75
Dept.
Science, Univ.
Self Assembled Acentric Multilayers Sinthesys
OH
OH
OH
O
O
O
Si
O
O
Si
Si
Si
O
O
OO
O
Si O
O
O
Si
Si O
Si
O
O
O
O O
O Si O Si O
Si O
Si
O
O O
O HO
OH
O
S
A
S
Capping
layer
Si
O
O
O
O
Si
Si
O
OH
N
N
M
O
N
O
L
A
Y
E
R
Me
Chromophore
layer
Coupling
layer
Me
N
N
Me
N
N
Repeat
O
N
N
N
I
I
I
Si O
O
O
Si O
O
O
SAS
Si O
O
SA-PEPOH
76
Dept.
Science, Univ.
Self Assembled Acentric Multilayers Synthesis
repeat
(i)
(iii)
(ii)
(i-iii)
Substrate
(i) Coupling reagent,
(ii) Organic Chromophore,
(iii) Capping reagent,
I
O
N
SiX3
Et
O
R
S
HCN
OH
OH
Cl
Cl
Cl
Si
O
Cl
Si Cl
O
Cl
Si
Cl
Cl
X = Cl, I, OR
77
Dept.
Science, Univ.
Self Assembled Acentric Multilayers
Characterization
N
N
Me
SA-PEPOH2
N
N
SA-AZO
N
N
N+ X-
1
2
3
4
5
78
Dept.
Science, Univ.
Characterization
Surface Morphology
Atomic Force Microscopy (AFM)
Film Composition
X-Ray Photoelectron Spectroscopy (XPS)
Thickness, Roughness
X-Ray Reflectivity (XRR, AFM)
Wettability
Contact Angle Measurements (ACA)
Chromophore Density
Optical Transmission Spectroscopy (UV-VIS)
Chromophore Alignment
Second Harmonic Generation (SHG)
Facchetti, A.; Abbotto, A.; Beverina, L.; Van der Boom, M. E.; Dutta, P.; Evmenenko, G.;
Pagani, G. A.; Marks, T. J. Chem. Mater. 2003, 15(5), 1064-1072.
79
Dept.
Science, Univ.
Characterization – Film quality and regular growth
UV-Vis
(Absorption)
A b so rb an ce
0,16
0,14
0,12
y = 0,0249x
R2 = 0,9731
SA-PEPOH
0,10
0,08
0,06
0,04
0,02
N
0,00
0
1
2
3
4
5
6
CH3
N
N
n°of Trilayers
200
XRR
(Thickness)
Thickness (A)
180
160
HO
y = 33.845x
2
R = 0.9831
140
120
100
80
60
40
20
0
0
1
2
3
4
5
6
n° of Trilayers
80
Dept.
Science, Univ.
OH
Characterization – Film morphology
1.0 µm
1.0 µm
1 layer
0
2 layers
3 layers
AFM of SA PEP-OH
on Silicon Substrates
Layers
4 layers
5 layers
1
2
3
4
5
RMS (Å)
2.4
4.8
7.0
8.9
11.2
81
Dept.
Science, Univ.
Characterization - SHG
SA-PEPOH
N
CH3
N
N
HO
2)
χ (zzz
=
10-8
31 x
esu
(128 pm/V)
OH
SHG Response (a. u.)
5
y = 0.7159x
4
2
R = 0.9886
3
2
1
0
0
1
2
3
4
5
6
n°of Trilayers
82
Dept.
Science, Univ.
Is the story over? NO!
1. Consider the Gymn of the monopodal and of the
bipodal
2. Why not being Bio-inspired?
eM
N
Me
N
N
N
I
I
iS
O
Si
O
O
O
O
O
SA - 2
83
Dept.
Science, Univ.
UV-Vis Characterization: solution
Me
N
Me
N
Me
Me
N
Me
N
N
Me
N
N
Me
Me
N
N
N
3
I
N
1
N
N
I
N
I
N
4
Me
N
2
Me
N
Me
N
5
I
Me
N
Me
N
Me
N
I
I
6
84
Dept.
Science, Univ.
Me
Dibranched Chromophore Architecture on
Covalent Self-Assembly, Thin-Film Microstructure
Me
N
Me
N
Me
N
N
N
Me
N
Me
N
N
Me
N
Me N
N Me
N Me
0,35
Absorbance (a. u.)
0,30
CH2
Me
0,25
N
Me
N
0,20
0,15
N
N
Si O
O
O
0,10
0,05
O
0,00
300
350
400
450
500
550
Si O
O
600
Wawalength (nm)
Facchetti, A.; Beverina, L.; Van der Boom, M. E.; Dutta, P.; Evmenenko, G.; Shukla, A. D.; Stern, C. E.; Pagani, G. A.;
Marks, T. J. J. Am. Chem. Soc. 2006, 128(6), 2142-2153.
85
Dept.
Science, Univ.
UV-Vis Characterization: SA films
Me
Me
N
N
Me
N
N
O
H
O
H
O
N
N
I
I
O
Me
N
N
I
I
Si
O O
O
H
Si
O O
O
Si
O O
O
SA-1
Me
Me
Substrate
Me
Me
N
N
N
N
N
N
Me
I
I
N
I
I
O
Me
I
N
(i)
I
Si
O O
I
Si
O O
O
Si
O O
O
Si
O O
O
Si
O O
I
SA-3
N
O
Si
O O
O
Si
O O
SA-IBnS
Me
(ii)
N
Me
N
N
O
Si
O O
Si
O O
O
N
I
I
I
O
N
Me
N
N
I
I
N
Si
O O
O
Si
O O
O
Si
O O
SA-2
N
I
I
Si
O O
I
I
I
I
O
N Me
N
Me
N Me
N
Me
N
O
Si
O O
O
Si
O O
O
Si
O O
SA-4
86
Dept.
Science, Univ.
SA films Characterization: SHG signals
2)
χ (zzz
esu
(140
pm/V)
2.0
2.0
1.6
1.2
0.8
0.4
0.0
= 34 x 10-7
N
1.6
CH3
N
1.2
0.8
0.4
0.0
0
10
20
30
40
50
Angle of Incidence (°)
60
70
0
10
20
30
40
50
60
70
Angle of Incidence (°)
87
Dept.
Science, Univ.
Case 2 study of NLO Phoenomena:
MULTIPHOTON PROCESSES
excited
state
3-D micro and nano-fabrication;
MEMS, bioMEMS: lab-on-a-chip
800
nm
ground
state
Optical limiting via
two photon absorption
Perry et al Nature 1999, 398, 51-54.
IR Imaging in tissues – Immunological Assays
600
Output Intensity (GW/cm2)
solvente
500
400
300
200
100
0
0
200
400
600
800 1000 1200 1400 1600 1800
Input Intensity (GW/cm2)
……really,a new challenge for organic materials !
88
Dept.
Science, Univ.

speed of light

Transcript

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