U.S. patent application number 11/982979 was filed with the patent office on 2008-07-17 for vapor deposited electro-optic films self-assembled through hydrogen bonding.
Invention is credited to Tobin J. Marks, Peiwang Zhu.
Application Number | 20080171146 11/982979 |
Document ID | / |
Family ID | 32962546 |
Filed Date | 2008-07-17 |
United States Patent
Application |
20080171146 |
Kind Code |
A1 |
Marks; Tobin J. ; et
al. |
July 17, 2008 |
Vapor deposited electro-optic films self-assembled through hydrogen
bonding
Abstract
The present invention introduces a novel route toward
microstructural orientation into organic films, using multiple
hydrogen-bonding to self-assemble chromophore molecules into
electro-optic films in a net polar orientation. High-quality, thick
films (up to micrometers) with molecular net dipole orientations
can be fabricated under vacuum in hours. The film microstructure is
intrinsically acentric; and the orientation is robust.
Inventors: |
Marks; Tobin J.; (Evanston,
IL) ; Zhu; Peiwang; (Evanston, IL) |
Correspondence
Address: |
REINHART BOERNER VAN DEUREN S.C.;ATTN: LINDA KASULKE, DOCKET COORDINATOR
1000 NORTH WATER STREET, SUITE 2100
MILWAUKEE
WI
53202
US
|
Family ID: |
32962546 |
Appl. No.: |
11/982979 |
Filed: |
November 6, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10789928 |
Feb 27, 2004 |
7291293 |
|
|
11982979 |
|
|
|
|
60450907 |
Feb 28, 2003 |
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Current U.S.
Class: |
427/255.6 |
Current CPC
Class: |
C09B 23/0066 20130101;
G02F 1/3612 20130101; C07D 403/10 20130101 |
Class at
Publication: |
427/255.6 |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Goverment Interests
[0002] The United States government has certain rights to this
invention pursuant to Grant No. N00014-00-C-0528 from the Office of
Naval Research to Northwestern University.
Claims
1. A method of using hydrogen-bonding for acentric chromophore
orientation, said method comprising: providing a substrate
comprising one of a hydrogen bond-forming hydrogen donor moiety and
a hydrogen bond-forming hydrogen acceptor moiety; contacting said
substrate with a vapor phase chromophore compound having a first
terminal moiety comprising a plurality of hydrogen bond-forming
hydrogen donor groups, and a second terminal moiety comprising a
plurality of hydrogen bond-forming hydrogen acceptor groups; and
contacting said first chromophore compound with a second said vapor
phase chromophore compound, wherein said first and second
chromophore compounds are of a formula D-Ar.sup.1.sub.x X.dbd.X
.sub.nAr.sup.2.sub.y-A wherein D is a moiety comprising a plurality
of hydrogen bond-forming hydrogen donor groups; A is a moiety
comprising a plurality of hydrogen bond-forming hydrogen acceptor
groups; (--X.dbd.X--) is a .pi.-bonded component comprising at
least one of carbon and a heteroatom; n, x and y are independently
.gtoreq.0; and x+y is .gtoreq.1.
2. The method of claim 1 wherein said first terminal moiety is
selected from ##STR00004## wherein R.sub.1-R.sub.3 are
independently selected from hydrogen, electron-donating
substituents and electron-withdrawing substituents.
3. The method of claim 1 wherein said second terminal moiety is
selected from ##STR00005## wherein R.sub.7 is selected from
hydrogen, electron-donating substituents and electron-withdrawing
substituents.
4. The method of claim 1 comprising providing a substrate
comprising hydroxy moieties, reacting said moieties with an
aminoalkyltrialkoxysilane, and reacting said hydroxy-silane
reaction product with a melamine moiety, for hydrogen-bonding with
said chromophore.
Description
[0001] This application is a divisional of and claims priority
benefit from application Ser. No. 10/789,928 filed Feb. 27, 2004,
and issued Nov. 6, 2007, as U.S. Pat. No. 7,291,293, which claimed
priority from provisional application Ser. No. 60/450,907, filed
Feb. 28, 2003--and each of which is incorporated herein by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0003] Molecule-based photonic materials represent a promising
direction in the quest to develop novel electro-optic (EO)
modulators promising greatly increased rates of information
transmission by enhancing optical network speed, capacity, and
bandwidth for data networking and telecommunications.
Non-centrosymmetry is one of the basic requirements of these
materials. Currently, three major methodologies are being used to
achieve molecular orientation: electric-field (EF) poling,
Langmuir-Blodgett (LB) film transfer, and layer-by-layer
self-assembly (SA). In the first one, nonlinear optical
(NLO)-active chromophores are either doped in or covalently bonded
to a polymer to fabricate films. A high external electric field is
then applied while the films are heated to around the glass
transition temperature (Tg) to cause the chromophore dipoles to
align in the direction of the electric field. It is a
straightforward procedure to fabricate thick-poled films. However,
the drawbacks are: 1) the orientation achieved by EF-poling is not
indefinitely stable after removal of the EF; 2) due to strong
dipole-dipole interactions among the chromophore molecules, the
doping concentration cannot be brought to a high level; 3)
micro-domains formed during EF-poling can increase the optical loss
in a waveguide device.
[0004] For the LB film approach, only limited chromophores with
long alkyl groups can be used. Since weak van der Waals
interactions are the main structural driving force, the orientation
becomes progressively worse as the film becomes thicker (e.g.,
after 100 layers). Other drawbacks include low NLO response and
poor mechanical strength. For covalent self-assembly, the NLO
response is strong, orientation is stable, and film quality is
good. However, the main disadvantage is the time-consuming nature
of the fabrication procedure (hundreds of hours might be used to
achieve a micrometer thickness film). Additional synthetic
complexity arises from use of moisture-sensitive reagents.
[0005] Although H-bonds are widely used in crystal engineering, the
prior art is not directed to thin film deposition using H-bonding
constituents. Since thin acentric films are needed for EO
modulators, efficient new depositions methods would be of great
utility. Dipolar orientations driven by H-bonds have been reported
in drop-cast films. However, the H-bonding modules come from two
different compounds (FIG. 1, structure A), and the films obtained
are composites, and not derived from the vapor phase. A technique
known as "oblique incidence organic molecular beam deposition" was
also reported to produce oriented films with single H-bonds used to
align chromophore molecules (FIG. 1, Structure B). However, the
molecular dipoles are parallel to the substrate. Only in-plane
directional ordering is achieved (FIG. 1, structure B). As is well
known, in a waveguiding EO modulator device, the molecular dipoles
must be oriented perpendicular to the substrate plane so that
maximum EO coefficient, r.sub.33, can be achieved.
[0006] Vapor deposition techniques have previously been used in the
art to fabricate ordered NLO organic films, such as stilbazolium
salts, polydiacetylenes, etc; however, the driving forces do not
involve H-bond formation. In stilbazolium salt films, the
chromophore is generated in situ, and in ordered polydiacetylene
films, van der Waals interactions play important roles. Reaction
considerations limit the former, while unstable structural
orientations plague the latter. As a result, the art continues its
search for a facile assembly of robust films of NLO-active
chromophores.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1. Prior art structures A and B, in comparison with
structure C, as represented illustrating multiple H-bonds between
5-{4-[2-(4,6-diamino-[1,3,5]triazin-2-yl)-vinyl]-benzylidene}-pyrimidine--
2,4,6-trione (DTPT) molecules, in accordance with this
invention.
[0008] FIG. 2. A schematic representation illustrating orientation
of a chromophore of this invention, on a substrate.
[0009] FIG. 3. UV-vis spectrum of vapor deposited DTPT film on
quartz.
[0010] FIG. 4. SHG response as a function of fundamental beam
incident angle from a float glass slide having a 1220 nm thick DTPT
film on one side.
[0011] FIG. 5. Square root of second harmonic generation (SHG)
response of DTPT films as a function of the thickness; Inset: SHG
response as a function of fundamental beam incident angle from a
float glass slide having DTPT films at the indicated thickness on
both sides. The dashed line is drawn as a guide to the eye. The
solid line is fitting result.
[0012] FIG. 6. X-ray diffraction pattern of a DTPT film grown on a
functionalized Si (100) substrate; Inset: Proposed molecular
alignment in film.
[0013] FIG. 7. AFM image at 5.times.5 .mu.m scan area of a DTPT
film.
[0014] FIG. 8. A schematic formula, in accordance with certain
embodiments of this invention.
[0015] FIG. 9. With reference to FIG. 8, molecular structures of
several general NLO-active core components of chromophores, in
accordance with this invention, where R.sub.1-R.sub.3 are
independently selected from H, alkyl, electron-donating
substituents or electron withdrawing substituents, and m and n are
integers described elsewhere herein.
[0016] FIGS. 10A-10B. With reference to FIG. 8, molecular
structures of several D (FIG. 10A) and A (FIG. 10B)
moieties/modules. 10A: R.sub.1 and R.sub.2 are independently
selected from H, alkyl or other electron-donating or withdrawing
substituent groups. One of the substitutents groups R.sub.3,
R.sub.4, and R.sub.5, is Ar.sup.1. 10B: one of the substitutents
R.sub.6, R.sub.7, and R.sub.8 is Ar.sup.2; X may be O or S.
SUMMARY OF THE INVENTION
[0017] In light of the foregoing, it is an object of the present
invention to provide acentric electro-optic films and/or compounds,
compositions, composites and/or methods for their production and/or
assembly, thereby overcoming various deficiencies and shortcomings
of the prior art, including those outlined above. It will be
understood by those skilled in the art that one or more aspects of
this invention can meet certain objectives, while one or more other
aspects can meet certain other objectives. Each objective may not
apply equally, in all its respects, to every aspect of this
invention. As such, the following objects can be viewed in the
alternative with respect to any one aspect of this invention.
[0018] It is an object of the present invention to provide a
molecular-based electro-optic film with a stable, microstructural
polar orientation without resort to time-consuming fabrication
procedures of the prior art.
[0019] It is another object of this invention to provide one or
more class of compounds for use in the self-assembly of
multi-layered compositions, as can be used in the preparation of a
range of electro-optic films, composites and/or modulator
devices.
[0020] Other objects, features, benefits and advantages of the
present invention will be apparent from this summary and its
descriptions of various embodiments and will be readily apparent to
those skilled in the art having knowledge of various electro-optic
films, modulators, related devices and associated
assembly/production techniques. Other objects, features, benefits
and advantages will be apparent from the above as taken into
conjunction with the accompanying examples, data, figures and all
reasonable inferences to be drawn therefrom.
[0021] The present invention relates to the use of multiple
hydrogen-bond donors and acceptors in an NLO active chromophore
molecular core. Specifically designed intermolecular H-bonds
provide chromophore alignment in the desired direction (head-tail
and perpendicular to the substrate plane) from vapor phase to form
solid films (FIG. 1, structure C). Out-plane non-centrosymmetric
microstructures are achieved in the deposited films, and this
acentricity is intrinsic. H-bonding, stronger than van der Waals
forces, provides a dipole orientation stable with time, and results
in good film mechanical strength. The chromophores are not
moisture-sensitive, and the films are convenient to handle. Vapor
deposition techniques can be adopted to fabricate films. The
process is rapid using available synthetic techniques (micrometer
thick films can be deposited in hours), and the film surface is
quite smooth (the rms roughness is only a few nanometers for a
micrometer thick film). This invention provides the first use of a
plurality of H-bonds as a driving force and/or enroute to the
preparation of microstructurally acentric (with the net dipolar
orientation perpendicular to the substrate surface) self-assembled
films from the vapor phase.
[0022] With reference to the preceding, the present invention
comprises compounds which can be represented by a formula
D-Ar.sup.1.sub.x--(X.dbd.X).sub.n--Ar.sup.2.sub.y-A (1)
wherein D is a moiety with a plurality of functional groups capable
of hydrogen donation; Ar.sup.1 and Ar.sup.2 are aromatic or
heterocyclic moieties; X is carbon or a heteroatom component
providing .pi.-bonding capability; n is an integer greater than or
equal to 0; x and y are independently integers greater than 0,
providing their sum is at least 1; and A is a moiety with a
plurality of functional groups capable of hydrogen-acceptance in
the formation of a hydrogen bond. With reference to the compounds
of formula I, the Ar and X components can be considered as
comprising a core chromophore molecular structure, as discussed
elsewhere herein, in the context of an NLO material. Without
limitation reference is made to FIGS. 8 and 9, the latter of which
provides a number of such core molecular structures. As illustrated
by FIG. 9, Ar.sup.1 and Ar.sup.2 can be but are not limited to
phenyl, naphthyl, pyridine, pyrimidine and thiophene and other
aromatic, polycyclic and heterocyclic moieties, wherein R.sub.1,
R.sub.2 and R.sub.3, etc. can be hydrogen or a substituent provided
for desired structural or electronic (e.g., electron-donating or
electron-withdrawing, as would be understood by those in the art)
effect. Likewise, with reference to FIG. 9, it will be understood
by those skilled in the art that a plurality of such aromatic or
heterocyclic moieties can be structurally coupled to one or more
.pi.-bonding components with a corresponding number of single- or
multiple-bond components, whether or not conjugated with Ar.sup.1
and/or Ar.sup.2. Such NLO-active core structures can vary or be
designed to optimize nonlinearity, working wavelength, stability
and associated electro-optic properties.
[0023] Without limitation, representative hydrogen-donor (D) and
acceptor (A) moieties are shown, respectively, in FIGS. 10A-10B.
Compounds 1, above, can be prepared incorporating such and other
donor and acceptor moieties using well-known synthetic precursors
and prepatory techniques, including but not limited to the coupling
or condensation reactions and related procedures illustrated in
Scheme 1, such procedures as can be varied without undue
experimentation by choice of hydrogen donor, acceptor
carbon/heteroatom component and aromatic heterocyclic moiety
precursors, appropriately substituted for such reaction, en route
to a particular compound of formula 1.
[0024] With reference to the preceding discussion of compounds 1,
structural modules/components/moieties and variations thereof and
related precursors and synthetic techniques, the present invention
can also be extended to include compounds 2-4, as can be
represented by the respective structural formulae:
D-Ar.sup.1--(X.dbd.X).sub.n--Ar.sup.2-A (2)
D-Ar.sup.1--(X.dbd.X).sub.n-A (3)
D-(X.dbd.X).sub.n--Ar-A (4)
Depending upon the particular chromophore, single Ar.sup.1 or
Ar.sup.2 moieties can be used in conjunction with a molecularly
non-elongated (e.g., n=1) .pi.-bonded component.
[0025] In part, the present invention can also include a method of
using hydrogen-bonding for acentric chromophore molecular alignment
perpendicular to a substrate plane. Such a method includes (1)
providing a dipolar chromophore molecular component having a first
terminal moiety with a plurality of functional groups capable of
hydrogen donation, and a second terminal moiety with a plurality of
functional groups capable of hydrogen acceptance; (2) contacting a
substrate with such a chromophore molecular component, the
substrate functionalized for hydrogen-bonding (e.g., for hydrogen
donation or hydrogen acceptance) with the molecular component; and
(3) contacting the molecular component with another such dipolar
chromophore molecular component. In various embodiments, the
chromophore components have acentric molecular structures, assembly
of which in accordance with the present methodologies can provide
corresponding multi-layered acentric films or coatings having a net
dipolar orientation perpendicular to the plane of an associated
substrate.
[0026] Molecular components useful with such a method include but
are not limited the compounds of formulae 1-4, above. Identity of
the terminal hydrogen donor and acceptor moieties are a matter of
choice depending upon the degree of required hydrogen-bonding and
desired chromophore core structures. As discussed elsewhere herein,
such compounds and related methodologies can be utilized in the
fabrication of a wide range of second-order NLO devices and
associated multi-layered compositions and composites where smooth,
transparent acentric films are required. Applications include but
are not limited to electro-optic modulators, devices for doubling
the frequency of lights and second harmonic generation.
EXAMPLES OF THE INVENTION
[0027] The following non-limiting examples and data illustrate
various aspects and features relating to the compounds, composites
and/or methods of the present invention, including the
self-assembly of intrinsically acentric electro-optic media, as are
available through the synthetic methodologies described herein. In
comparison with prior art, the present methods and
compounds/composites provide results and data which are surprising,
unexpected and contrary thereto. While the utility of this
invention is illustrated through the use of several
compounds/composites and synthetic methods which can be used in
conjunction therewith, it will be understood by those skilled in
the art that comparable results are obtainable with various other
compounds/compositions and associated methods, as are commensurate
with the scope of this invention.
[0028] Materials and methods. Unless stated otherwise, chemicals
were purchased from Aldrich Chemical Co. and used as received.
Single-crystal silicon (100) substrates were purchased from
Semiconductor Processing Company, Inc. NMR spectra were recorded on
a Varian Mercury-400 MHz or Varian INOVA-500 MHz spectrometer. Mass
spectra were recorded with a Micromass Quattro II Triple Quadrupole
HPLC/MS/MS Mass Spectrometer. Elemental analyses were performed by
Midwest Microlabs. UV-vis spectra were recorded on a Cary 1E
spectrophotometer. Polarized second harmonic generation
measurements were carried in the transmission mode with a
Q-switched Nd:YAG laser operating at 1064 nm, with a pulse width of
3 ns at a frequency of 10 Hz. Atomic force microscopic images were
recorded with a Nanoscope II instrument (Digital Instruments,
Inc.).
Example 1
[0029] Illustrating one aspect of this invention is the design of a
class of NLO-active chromophores containing multiple H-bond donors
and acceptors: for example,
5-{4-[2-(4,6-diamino-[1,3,5]triazin-2-yl)-vinyl]-benzylidene}-pyrimidine--
2,4,6-trione (DTPT, shown below). In this chromophore molecule,
pyrimidine-2,4,6-trione and 4,6-diamino-1,3,5,-triazine moieties
can form triple H-bonds between two neighboring molecules (FIG. 2).
A head-tail structural configuration is provided by choice and
design of the donor and acceptor moieties.
Example 2a
[0030] Synthetic Procedures. With reference to examples 2(b-c)
below, one chromophore of this invention can be prepared according
to the synthetic route illustrated in Scheme 1.
##STR00001##
This generally synthetic procedure and modifications thereof, as
would be understood by those in the art, can be used en route to a
range of acentric chromophore compounds, in accordance with this
invention, such compounds as can vary depending upon choice of the
aforementioned D, A, Ar.sup.1, Ar.sup.2 and .pi.-bonding moieties
or components.
Example 2b
[0031] Synthesis of
4-[2-(4,6-diamino-[1,3,5]triazin-2-yl)-vinyl]-benzaldehyde. To
107.2 g (800 mmol) of benzene-1,4-dicarboxaldehyde suspended in 450
mL methanol was added with stirring 294.0 g of 31% aqueous sulfuric
acid (50 mL of concentrated sulfuric acid was added slowly to 200
mL of water while stirring). The solid dissolved and a yellow
solution was obtained. The solution was heated to 80.degree. C.
with an oil bath, and 25.0 g (200 mmol)
6-methyl-[1,3,5]triazine-2,4-diamine powder was added. The solution
was stirred at 80.degree. C. for 8 h then cooled to room
temperature. Next, 1.2 g of yellow byproduct
(1,4-bis[4-[2-(4,6-diamino-[1,3,5]triazin-2-yl)-vinyl]]-benzene)
was removed by filtration, and the filtrate was treated with 2000
mL water. The resulting solid was collected by filtration and
washed with saturated aqueous NaHCO.sub.3 and water until neutral.
The excess benzene-1,4-dicarboxaldehyde was removed by sonicating
and washing with acetone three times. Yield: 20.0 g of light yellow
product. Yield=41%. .sup.1HNMR (500 MHz, DMSO): .delta.9.992 (s,
1H), 7.894 (d, J=8.0 Hz, 2H), 7.847 (d, J=7.5 Hz, 2H), 7.806 (d,
J=15.5 Hz, 1H), 6.928 (d, J=15.5 Hz, 1H), 6.806 (br, 4H).
.sup.13CNMR (500 MHz, DMSO): .delta.193.914, 193.417, 170.671,
167.847, 141.836, 136.833, 131.461, 130.688, 128.883.
Example 2c
[0032] Synthesis of
5-{4-[2-(4,6-Diamino-[1,3,5]triazin-2-yl)-vinyl]-benzylidene}-pyrimidine--
2,4,6-trione (DTPT). To 7.29 g (30 mmol) of
4-[2-(4,6-diamino-[1,3,5]triazin-2-yl)-vinyl]-benzaldehyde
suspended in 150 mL of 1-pentanol at 130.degree. C. was cautiously
added 75 mL of hot aqueous sulfuric acid (25 mL of concentrated
sulfuric acid was added to 50 mL of water with cautious while
stirring). The solid dissolved immediately, and a yellow solution
was obtained. To this solution, 4.61 g (36 mmol) of powdered
barbituric acid was added while stirring vigorously at 140.degree.
C. Yellow precipitate appeared immediately. The mixture was
slightly refluxed at 140.degree. C. for 10 min then filtrated while
it was hot. Solid was washed with 50 mL of warm 1-pentanol, then
suspended in 300 mL of water and neutralized with saturated aqueous
NaHCO.sub.3. The solid was collected by filtration and washed with
water. Yield: 9.72 g of yellow product. Yield=88%. .sup.1HNMR (400
MHz, DMSO): .delta.11.519 (s, 1H), 11.375 (s, 1H), 8.378 (s, 1H),
8.234 (d, J=8.0 Hz, 2H), 7.915 (d, J=16.0 Hz, 1H), 7.857 (d, J=8.0
Hz, 2H), 7.101 (br, 4H), 7.047 (d, J=16.0 Hz, 1H). m.p.
>350.degree. C. EA found: C, 52.20; H, 3.86; N, 26.12.
Calculated for C.sub.16H.sub.13N.sub.7O.sub.3.H.sub.2O: C, 52.03;
H, 4.09; N, 26.55. MS (rel. abundance): M.sup.++1 (68), M.sup.++2
(13), 242.1 (5), 217.1 (6), 179.0 (15), 157.0 (30), 101.0 (55),
79.1 (100). MS (high resolution, ES.sup.+): MH.sup.+
(352.1158).
Example 3a
[0033] Substrate Preparation and Functionalization. With reference
to examples 3b-3d, a melamine template was anchored on substrates
according to Scheme 2, illustrating a general methodology for
substrate functionalization.
##STR00002##
Example 3b
[0034] Cleaning of substrates. Sodium lime glass, fused quartz, and
silicon wafer substrates were cleaned by immersion in "piranha"
solution (H.sub.2SO.sub.4/30% H.sub.2O.sub.2 7:3 (v/v)) (Caution:
"Piranha" is an extremely dangerous oxidizing agent and should be
handled with care using appropriate shielding) at 80.degree. C. for
1 h. After cooling to room temperature, they were rinsed with
deionized water and then subjected to an RCA-type cleaning protocol
(NH.sub.3.H.sub.2O/H.sub.2O/30% H.sub.2O.sub.2 1:5:1 (v/v) at room
temperature, 40 min). They were then washed with deionized water
and dried in oven at 125.degree. C. overnight. ITO glass
substrates, as illustrated above, were first sonicated in aqueous
detergent for 30 mins, then rinsed with deionized water. They were
then sonicated in methanol, iso-propanol, and acetone for 30 min,
respectively, and then dried in oven at 125.degree. C. overnight.
Other substrates suitable for use in conjunction with the present
invention are provided in the U.S. Pat. No. 5,834,100, the entirety
of which is incorporated herein by reference, such substrates as
can be modified/functionalized as illustrated herein.
Example 3c
[0035] Self-Assembly of 3-aminopropyltrimethoxysilane. Substrates
were loaded in an air-free reactor. The air inside of the reactor
was replaced by dry N.sub.2 using a Schlenk line. Then, 210 mL of
5% (v/v) 3-aminopropyltrimethoxysilane as a dry THF solution was
transferred to the reactor. The solution was heated at 60.degree.
C. for 24 h. After that, the substrates were rinsed three times
with THF. Alternatively, room temperature solution of 196 mL of 95%
ethanol and 4 mL of 3-aminopropyltrimethoxysilane was allowed to
stand for 10 min to ensure silanol formation. The substrates were
then immersed in this solution for 10 min. They were next rinsed
three times with 95% ethanol and dried in a dry N.sub.2 dtream, and
cured for 10 min in a vacuum oven at 110.degree. C.
Example 3d
[0036] Surface functionalization with
6-chloro-1,3,5-triazine-2,4-diamine. A solution was prepared from
1.46 g (8.14 mmol) of 6-chloro-1,3,5-triazine-2,4-diamine and 0.410
g (5.00 mmol) NaOAc in 200 mL DMSO. The substrates were immersed in
the solution for 24 h at room temperature. They were then washed
with DMSO, water, and then acetone. Alternatively, the reagent
(0.15 g) was suspended in 50 mL of 1-pentanol at 150.degree. C. The
3-aminopropyltrimethoxysilane functionalized substrates were then
loaded into the reactor. After refluxing for 24 h, they were cooled
to room temperature and rinsed with 1-pentanol, deionized water,
and acetone. Functionalization with a suitable hydrogen acceptor
can be provided as would be understood by those in the art aware of
this invention.
Example 4a
[0037] Sublimation of DTPT. To achieve further purification and to
ascertain that DTPT (example 2c) is stable under sublimation
conditions, the chromophore was gradient sublimed at 330.degree.
C./.about.3.times.10.sup.-8 Torr for 24 h. The .sup.1H NMR spectrum
of the sublimed material is identical to that prior to sublimation.
EA found: C, 54.21; H, 3.61; N, 26.60. Calculated for
C.sub.16H.sub.13N.sub.7O.sub.3: C, 54.70; H, 3.73; N, 27.91. This
result shows that the water of crystallization is lost on
sublimation.
Example 4b
[0038] Film Deposition. Scheme 3 depicts an apparatus
configuration, of the sort commercially available, which can be
used to vapor deposit and grow the chromophore films of this
invention. Vacuum pressures can typically range from about
10.sup.-5.about.10.sup.-6 Torr, with a substrate temperature
depending upon choice of chromophore and substrate. A calibrated
quartz crystal balance was used to monitor the film growth rate and
thickness. More specifically, a Denton Vacuum DV-502 deposition
apparatus (10.sup.-5-10.sup.-6 Torr) was then used to fabricate
DTPT films at an optimized substrate temperature of 100.degree. C.
and growth rate of 0.5-2.0 .ANG./s which was controlled by
adjusting the heating current of the crucible. The resulting film
was optically transparent (.alpha..apprxeq.10 cm.sup.-1 at 640-1800
nm, .lamda..sub.max=332 nm) and smooth by contact mode AFM (see
Example 8, below). Deposit parameters and growth conditions will
vary depending upon choice of chromophone, as will be understood by
those skilled in the art made aware of this invention.
##STR00003##
Example 5
[0039] Optical UV-Vis Spectroscopy. Homogeneous substrate coverage
deepening of the yellow color of the films deposited on transparent
substrates can be clearly observed by eye. The film UV-vis spectrum
shows an absorption peak around 332 nm (FIG. 3), which is slight
blue shifted compared to the spectrum in DMSO solution.
Example 6
[0040] Second Harmonic Generation Experiments. Polarized
transmission SHG measurements on the films at .lamda..sub.o=1064 nm
were carried out on samples placed on a computer-controlled
rotation stage, enabling the incidence angle of the input radiation
to the sample surface normal to be varied from 0.degree. to
76.degree.. For a sample with a film deposited on only one side, it
shows the strongest SHG response at the incident angle about
50.degree. (FIG. 4). Angle-dependent SHG interference patterns for
glass substrates coated on both sides demonstrate that identical
film quality and uniformity on both sides of the substrate have
been achieved. A quadratic dependence of the 532 nm light output
intensity (I.sub.obs.sup.2.omega.) on the thickness of the DTPT
film (FIG. 5) further demonstrates the uniformity of the
chromophore orientation, and that the response is likely due to a
bulk rather than interface effect. Calibrating the data in FIG. 5
with quartz crystal SHG intensity gives a d.sub.33 of 0.15 pm/V and
d.sub.31 of 0.25 pm/V, values consistent with the modest computed
molecular hyperpolarizability [.beta..sub.tot(.omega.=0.0
eV)=81.times.10.sup.-30 esu for a linear trimer]. Using standard
assumptions, the SHG analysis yields an average chromophore tilt
angle of 56.7.degree. with respect to the substrate normal.
Example 7
[0041] X-ray Diffraction. Synchrotron X-ray diffraction (XRD) was
employed to probe microstructural similarity and determine the
degree to which the non-centrosymmetric crystal structure of DTPT
was achieved. In FIG. 6, a specular peak appears at 0.69
.ANG..sup.-1, which corresponds to a layer-by-layer structure with
a repeat distance of 9.1 .ANG.. AM1-level molecular modeling shows
the distance between DTPT molecules in a H-bonded chain is
.about.16.8 .ANG., which, combined with the XRD data yields a
molecular tilt angle from the substrate normal of 57.2.degree. in
the films. (See, FIG. 6 inset and the schematic representation of
FIG. 2.) This result is in good agreement with the SHG data of the
preceding example and clearly shows out-plane ordering of
chromophore molecules has been achieved and yields a similar tilt
angle.
Example 8
[0042] Atomic Force Microscopy. Contact mode AFM measurements on a
1.22 .mu.m thick film sample reveal a smooth, high quality film.
With a 5.0.times.5.0 .mu.m scan area, the rms roughness is only 1.7
nm (FIG. 7).
[0043] As shown above, illustrating broader aspects of this
invention, a donor-acceptor .pi. electron chromophore was designed
and synthesized. Multiple H-bonding interactions direct
self-assembled chromophore alignment in the desired molecular
head-to-tail direction using a straightforward vapor phase
deposition process. Angle-dependent SHG interference patterns for
glass substrates coated on both sides and the quadratic dependence
of the 2.omega. light output intensity on chromophore film
thickness demonstrate high, uniform film quality and polarity. XRD
also demonstrates long-range, acentric microstructural order and
yields a molecular tilt angle in good agreement with polarized SHG
data, demonstrating out-of-plane ordering of chromophore alignment,
of the sort useful in the context of electro-optic films and
related devices.
* * * * *