Organic nonlinear optical media

In one embodiment this invention provides a nonlinear optical medium consisting of a solid solution of components comprising (1) a thermoplastic polymer such as poly(methyl acrylate/butyl acrylate); (2) a first organic compound which exhibits nonlinear optical response such as 4-amino-4'-nitrostilbene; and (3) a second organic compound such as methyl acrylate which complexes with and enhances the nonlinear optical response of the first organic compound.

CROSS-REFERENCE TO RELATED APPLICATIONS 
The subject matter of this patent application is related to that disclosed 
in patent application S.N. 087,493, filed Aug. 20, 1987; which is 
incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
It is known that organic and polymeric materials wit large delocalized 
.pi.-electron systems can exhibit nonlinear optical response, which in 
many cases is a much larger response than by inorganic substrates. 
In addition, the properties of organic and polymeric materials can be 
varied to optimize other desirable properties, such as mechanical and 
thermoxidative stability and high laser damage threshold, with 
preservation of the electronic interactions responsible for nonlinear 
optical effects. 
Thin films of organic or polymeric materials with large second-order 
nonlinearities in combination with silicon-based electronic circuitry have 
potential as systems for laser modulation and deflection, information 
control in optical circuitry, and the like. 
Other novel processes occurring through third-order nonlinearity such as 
degenerate four-wave mixing, whereby real-time processing of optical 
fields occurs, have potential utility in such diverse fields as optical 
communications and integrated circuit fabrication. 
Nonlinear optical properties of organic and polymeric materials was the 
subject of a symposium sponsored by the ACS division of Polymer Chemistry 
at the 18th meeting of the American Chemical Society, Sept. 1982. Papers 
presented at the meeting are published in ACS Symposium Series 233, 
American Chemical Society, Washington, D.C. 1983; incorporated herein by 
reference. 
Of related interest with respect to the present invention is the disclosure 
of U.S. Pat. No. 4,717,508, which describes optically transparent organic 
solid solutions which exhibit nonlinear optical response; incorporated 
herein by reference. 
There is continuing research effort to develop new nonlinear optical 
systems for prospective novel phenomena and devices adapted for laser 
frequency conversion, information control in optical circuitry, light 
valves and optical switches. The potential utility of organic materials 
with large second-order and third-order nonlinearities for very high 
frequency application contrasts with the bandwidth limitations of 
conventional inorganic electrooptic materials. 
Accordingly, it is an object of this invention to provide novel nonlinear 
optical media. 
It is another object of this invention to provide process embodiments for 
producing novel nonlinear optical media. 
It is another object of this invention to provide a transparent optical 
medium which is a composite of a microporous inorganic oxide glass and an 
incorporated organic solid solution containing an organic compound which 
exhibits nonlinear optical response. 
It is a further object of this invention to provide optical devices which 
contain a novel nonlinear optical element. 
Other objects and advantages of the present invention shall become apparent 
from the accompanying description and examples 
DESCRIPTION OF THE INVENTION 
One or more objects of the present invention are accomplished by the 
provision of a nonlinear optical medium consisting of a solid solution of 
components comprising (1) a thermoplastic polymer; (2) a first organic 
compound which exhibits nonlinear optical response; and (3) a second 
organic compound which complexes with and enhances the nonlinear optical 
response of the first organic compound. 
A solid solution exhibits third order nonlinear optical response when its 
macroscopic molecular configuration is centrosymmetric. 
A solid solution exhibits second order nonlinear optical response when its 
macroscopic molecular configuration is noncentrosymmetric. The 
noncentrosymmetry can be achieved by an external field-induced orientation 
of aligned molecules of the first organic compound in the solid solution. 
In another embodiment this invention provides a nonlinear optical medium 
consisting of a solid solution of components comprising (1) a 
thermoplastic polymer; (2) a first organic compound exhibiting nonlinear 
optical response which corresponds to the formula: 
##STR1## 
where R is hydrogen or a C.sub.1 -C.sub.20 alkyl substituent, and R.sup.1 
is hydrogen or a C.sub.1 -C.sub.4 alkyl substituent; and (3) a second 
organic compound which complexes with and enhances the nonlinear optical 
response of the first organic compound. 
In another embodiment this invention provides a nonlinear optical medium 
consisting of a solid solution of components comprising (1) a 
thermoplastic polymer; (2) a first organic compound exhibiting nonlinear 
optical response which corresponds to the formula: 
##STR2## 
where R is hydrogen or a C.sub.1 -C.sub.20 alkyl substituent, and X is a 
single bond or a vinylene bond; and (3) a second organic compound which 
complexes with and enhances the nonlinear optical response of the first 
organic compound. 
In an invention nonlinear optical medium, the first organic compound and 
the second organic compound each is present in a quantity between about 
5-25 weight percent based on the weight of solid solution. 
It is preferred that the second organic compound is present in a sufficient 
quantity to associate with all of the first organic compound molecules. 
Typically, the first and quantities. 
A present invention nonlinear optical medium can be in the form of an 
optically transparent thin film. The thin film can be produced by melt 
casting an invention solid solution on a substrate. In another method the 
thin film can be produced by dissolving the solid solution in an organic 
solvent, coating the resultant liquid medium on a substrate, and removing 
the solvent to provide a thin film of the reconstituted solid solution. 
Suitable solvents include acetone, butanol, tetrahydrofuran, 
dimethylacetamide, ethyl acetate, 1-methyl-2-pyrrolidinone, 
1-methyl-2-piperidine, gamma-butyrolactone, cyclohexanone, and the like. 
In another embodiment this invention provides a process for producing a 
nonlinear optical medium which comprises preparing a homogeneous blend of 
components comprising (1) an organic compound which exhibits nonlinear 
optical response, and (2) at least one polymerizable vinyl monomer; and 
subjecting the homogeneous blend to polymerization conditions to produce a 
solid solution of (a) a host thermoplastic polymer, and (b) a guest 
organic compound which exhibits nonlinear optical response and is 
associated with a molecular complexing quantity of residual polymerizable 
monomer. 
The residual polymerizable vinyl monomer in the solid solution is present 
in a quantity between about 0.8-1.5 moles per mole of guest organic 
compound. 
The olefinic unsaturation of the residual vinyl monomer facilitates the 
complexing association between the vinyl monomer and the guest organic 
compound. 
Illustrative of polymerizable vinyl monomers are alkyl acrylate, alkyl 
methacrylate, vinyl halide, acrylonitrile, methacrylonitrile, styrene, 
acrylamide, methacrylamide, N,N-dialkylacrylamide, 
N,N-dialkylmethacrylamide, alkyl vinyl ether, and the like. Mixtures of 
monomers can be utilized to produce copolymers. 
Polymerization conditions for preparing the polymers and copolymers are 
described in prior art such as U.S. Pat. Nos. 3,354,084; 4,115,339; 
4,254,249; 4,395,524; 4,717,508; and references cited therein. 
In a typical procedure, between about 0.05-1.0 weight percent, based on the 
monomer weight, of a free radical initiator is incorporated in the 
homogeneous blend of components, and polymerized at a temperature between 
about 15.degree.-100.degree. C. for a period of about 1-72 hours. Suitable 
free radical initiators include ammonium persulfate, dibenzoyl peroxide 
and azo-bis-isobutyronitrile. 
The initial liquid phase homogeneous blend of guest/host components and 
free radical initiator converts to a thermoplastic solid solution under 
polymerization conditions. The solid phase can be shaped into thin or bulk 
matrices by conventional means. 
In another embodiment this invention provides a nonlinear optical medium 
consisting of a composite composition of an inorganic glass monolith with 
a microporous structure containing an incorporated solid solution of 
components comprising (1) a thermoplastic polymer; (2) a first organic 
compound which exhibits nonlinear optical response; and (3) a second 
organic compound which complexes with and enhances the nonlinear optical 
response of the first organic compound. 
In another embodiment this invention provides a process for producing a 
nonlinear optical medium which comprises impregnating a microporous 
inorganic oxide glass monolith with a homogeneous solution of components 
comprising (1) an organic compound which exhibits nonlinear optical 
response, and (2) at least one polymerizable vinyl monomer; and subjecting 
the homogeneous solution to polymerization conditions to produce a solid 
solution in the microporous glass of (a) a host thermoplastic polymer, and 
(b) a guest organic compound which exhibits nonlinear optical response and 
is associated with a molecular complexing quantity of residual vinyl 
monomer. 
The type of polymerizable vinyl monomer and the polymerization conditions 
employed are as previously described hereinabove. 
In a further embodiment this invention provides an optical light switch or 
light modulator device with a nonlinear optical element consisting of a 
solid solution of components comprising (1) a thermoplastic polymer; (2) a 
first organic compound which exhibits nonlinear optical response; and (3) 
a second organic compound which complexes with and enhances the nonlinear 
optical response of the first organic compound. 
The term "solid solution" as employed herein refers to a homogeneous single 
phase alloy of guest organic compounds and host polymer components. The 
guest organic compounds are not detectable as physically discrete 
crystallites in the polymer matrix. Solid solutions are illustrated in 
U.S. 4,428,873. 
The terms "associated" or "molecular complexing" as employed herein with 
respect to first and second organic compounds in an invention solid 
solution refer to a molecular interaction that corresponds to a measured 
change in the solid state carbon-13 nuclear magnetic resonance (NMR) 
chemical shift of the nitro-carbon resonance of 2-methyl-4-nitroaniline as 
a reference standard of at least about 0.5 parts per million (ppm) at 
25.degree. due to the presence of the complexing organic molecules. 
The molecular interaction is characterized further by a measured increase 
in the linewidths of the 50 megahertz (MHz) solid state carbon-13 NMR 
spectrum of the nitro-carbon and amino-carbon resonances of 
2-methyl-4-nitroaniline of at least about one ppm at 25.degree. C. due to 
the presence of the complexing organic molecules. 
The term "transparent" as employed herein refers to an optical medium which 
is transparent or light transmitting with respect to incident fundamental 
light frequencies and created light frequencies. In a nonlinear optical 
device, a present invention nonliner optical element is transparent to 
both the incident and exit light frequencies, and the nonlinear optical 
element exhibits less than about 15 percent scattering of transmitted 
incident light. 
The term "external field" as employed herein refers to an electric, 
magnetic or mechanical stress field which is applied to a medium of mobile 
organic molecules to induce dipolar alignment of the molecules parallel to 
the field. 
Application of a DC electric field produces orientation by torque due to 
the interaction of the applied electric field and the net molecular dipole 
moment of the mobile organic molecules. The molecular dipole moment is due 
to both the permanent dipole moment (i.e., the separation of fixed 
positive and negative charge) and the induced dipole moment (i.e., the 
separation of positive and negative charge by the applied field). 
Application of an AC electric field also can induce bulk alignment. In 
this case, orienting torque occurs solely due to the interaction of the 
applied AC field and the induced dipole moment. Typically, AC field 
strengths exceeding 1 kV/cm at a frequency exceeding 1 KHz are employed. 
The external field-induced alignment of organic molecules in a present 
invention nonlinear optical medium can be accomplished by heating the 
solid solution near or above its softening point, applying an electric 
field with a pair of positioned electrodes, and cooling the solution to 
the solid phase while maintaining the externally applied electric field. 
This method provides a stable molecular orientation in the solid solution. 
Thermoplastic Polymer Component 
The thermoplastic polymer component of a present invention solid solution 
can be a homopolymer or a copolymer. 
It is essential that the host polymer component has a high level of 
solvating power with respect to the incorporated first and second organic 
compounds. Preferably, the thermoplastic polymer is selected to form an 
optically transparent solid solution with up to about 50 weight percent of 
the combined weight of guest organic compounds based on the weight of the 
solid solution. 
A typical thermoplastic polymer component has a weight average molecular 
weight in the range between about 5000 and 200,000. 
Illustrative of suitable polymers are polyacrylate, polymethacrylate, 
polyacrylamide, polymethacrylamide, polyacrylonitrile, 
polymethacrylonitrile, polyvinyl alkylate, polyvinyl halide, polyurethane, 
poly(alkyl vinyl ether), and the like. A selected thermoplastic polymer 
component must be capable of forming an optically transparent solid 
solution. 
A preferred type of thermoplastic polymer is a polyvinyl polymer which 
contains at least about 70 mole percent of one or more monomers selected 
from C.sub.1 -C.sub.6 alkyl acrylate, C.sub.1 -C.sub.6 alkyl methacrylate, 
acrylamide, methacrylamide, N,N-dimethylacrylamide, 
N,N-dimethylmethacrylamide, acrylonitrile and methacrylonitrile. 
NLO Responsive Organic Compound Component 
The organic compound component which contributes nonlinear optical response 
properties to a present invention solid solution optical medium generally 
is a small molecule having a molecular weight less than about 1000. 
The preferred NLO responsive molecule is one which has a charge asymmetric 
electronic structure consisting of an electron-withdrawing group which is 
in conjugation with an electron-donating group, and which exhibits a 
second order nonlinear optical susceptibility .beta. of at least about 
500.times.10.sup.-30 esu. 
Illustrative of suitable NLO responsive organic compounds are nitroaniline 
type structures such as 4-nitroaniline, 2-methyl-4-nitroaniline, 
1-dimethylamino-4-nitronaphthalene, 2-chloro-4-nitroaniline, 
N,N-dimethylamino4-nitrobenzene, 4-amino-4'-nitrostilbene, 
4-N,N-dimethylamino4'-nitrostilbene, and the like. 
Organic compounds which have exceptional nonlinear susceptibility 
properties are those having structures corresponding to the formula: 
##STR3## 
where R' is a substituent selected from hydrogen and (C.sub.1 -C.sub.20) 
alkyl groups. Illustrative of the above formulae are: 
13,13-diamino-14,14-dicyanodiphenoquinodimethane. 
13,13-di(dimethylamino)-14,14-dicyanodiphenoquinodimethane. 
13,13-di(diethylamino)-14,14-dicyanodiphenoquinodimethane. 
13,13-di(n-hexadecylamino)-14,14-dicyanodiphenoquinodimethane. 
13,13-diamino-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethane. 
13,13-di(dimethylamino)-14,14-dicyano-4,5,9,10tetrahydropyrenoquinodimethan 
e. 
13,13-di(diethylamino)-14,14-dicyano-4,5,9,10tetrahydropyrenoquinodimethane 
. 
13,13-di(n-hexadecylamino)-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodime 
thane. 
13,13-ethylenediamino-14,14-dicyanodiphenoquinodimethane. 
13,13-ethylenediamino-14,14-dicyano-4,5,9,10-tetrahydropyrenoquinodimethane 
. 
The diphenoquinodimethane compounds are more fully described in U.S. 
4,640,800. 
Complexing Organic Compound Component 
The organic compound component which associates and complexes with the NLO 
responsive organic compound component in a present invention solid 
solution optical medium generally is a small molecule having a molecular 
weight less than about 1000. 
The dipolarity of the complexing organic compound and its specific 
structural configuration provide the associative molecular interaction 
with the NLO responsive organic compound component. 
Suitable complexing organic compounds include C.sub.1 -C.sub.6 alkyl 
acrylate, C.sub.1 -C.sub.6 alkyl methacrylate, acrylamide, methacrylamide, 
N,N-dimethylacrylamide, N,N-dimethylmethacrylate, acrylonitrile, 
methacrylonitrile, alkyl vinyl ether, trioxane, urea, stilbene, aniline, 
nitroben-zene, 1,4-dimethoxybenzene, and the like. 
It is particularly preferred that a present invention solid solution 
contain a thermoplastic polyvinyl polymer component, and a complexing 
vinyl organic compound component which is selected to correspond 
substantially in structure to the primary monomeric unit in the 
thermoplastic polymer. This type of structural similarity appears to favor 
compatibility between the complexing organic compound and the 
thermoplastic polymer, and consequently to favor a desired high content of 
the NLO responsive organic compound component with which the vinyl organic 
compound is molecularly associated. 
Preparation Of Porous Inorganic Oxide Glass Monoliths 
The various methods for the manufacture of porous glass are reviewed in 
U.S. Pat. No. 4,528,010. The methods include the Vycor (Corning), chemical 
vapor deposition, white carbon, colloid silica, and silica gel procedures. 
One method of producing a porous glass body involves (1) forming an article 
of desired shape from a parent borosilicate glass; (2) thermally treating 
the glass article at a temperature of 500.degree.-600.degree. C. to 
separate the glass into a silica-rich phase and a silica-poor phase; (3) 
dissolving or leaching the silica-poor phase with acid to provide a porous 
structure composed of the silica-rich phase; and (4) washing to remove 
leaching residue, and then drying. 
Embodiments for production of porous inorganic oxide glass monoliths by 
leaching of a soluble phase from a solid glass structure are described in 
U.S. Pat. Nos. 2,106,744; 2,286,275; 2,303,756; 2,315,328; 2,480,672; 
3,459,522; 3,843,341; 4,110,093; 4,112,032; 4,236,930; 4,588,540; and 
references cited therein; incorporated herein by reference. 
U.S. Pat. No. 4,584,280 describes a process for preparing a transparent 
porous ceramic film which involves applying an anhydrous solution 
containing an organometallic compound and a multifunctional organic 
compound to a substrate; and then thermally decomposing the organic 
compounds. 
A more recent development is the "sol-gel" process for preparation of 
porous monolithic glasses and ceramics at moderate temperatures. The 
sol-gel procedure involves the formation of a three-dimensional network of 
metal oxide bonds at room temperature by a hydrolysis-condensation 
polymerization reaction of metal alkoxides, followed by low temperature 
dehydration. The resultant porous glass structure optionally can be 
sintered at elevated temperatures. 
In another embodiment this invention provides a process for producing a 
composite composition comprising a homogeneous inorganic oxide glass 
monolith with a microporous structure containing an organic component 
which exhibits nonlinear optical response, which comprises (1) hydrolyzing 
tetraalkoxysilane under acidic or basic pH conditions in a sol-gel 
reaction medium comprising water and a water-miscible organic solvent 
component until gellation of the reaction medium is completed; (2) 
removing the solvent medium to provide a porous glass monolith; (3) 
impregnating the porous glass monolith with an organic solution which 
exhibits nonlinear optical response; and (4) sealing the glass monolith 
outer surfaces. 
The term "homogeneous" as employed herein with reference to a porous glass 
monolith means that the inorganic oxide composition and the microstructure 
are substantially invariant throughout the monolith. 
Embodiments for production of porous inorganic oxide glass monoliths by the 
sol-gel process are described in U.S. Pat. Nos. 3,640,093; 3,678,144, 
3,681,113; 3,811,918; 3,816,163; 3,827,893; 3,941,719; 4,327,065; 
4,389,233; 4,397,666; 4,426,216; 4,432,956; 4,472,510; 4,477,580; 
4,528,010; 4,574,063; and references cited therein; incorporated herein by 
reference. Mat. Res. Soc. Symp. Proc., 73, 35 (1986) by Hench et al 
describes the role of chemical additives in sol-gel processing; 
incorporated herein by reference. 
Illustrative of water-miscible solvents employed in a sol-gel process 
embodiment are alkanols such as methanol and ethanol; ketones such as 
acetone and methyl ethyl ketone; esters such as methyl acetate and ethyl 
formate; ethers such as dioxane and tetrahydrofuran; amides such as 
dimethylformamide, dimethylacetamide and 1-methyl-2-pyrrolidinone; and the 
like. 
Acidic pH conditions in the sol-gel process can be provided by the addition 
of mineral acids such as hydrochloric acid; and basic pH conditions can be 
provided by the addition of bases such as ammonium hydroxide. 
Illustrative of tetraalkoxysilanes and other metal and metalloid alkoxides 
are methoxy and ethoxy derivatives of silicon, lithium, magnesium, 
titanium, manganese, aluminum, tin, antimony, and the like. Aryloxy 
derivatives also can be utilized in the sol-gel process. 
Porous glass monoliths produced by a sol-gel process embodiment have an 
advantageous combination of properties, and generally have superior 
optical properties as compared to porous glass monoliths prepared by other 
techniques, e.g., by the leaching of a silica-poor phase from a 
borosilicate glass. 
A sol-gel derived porous glass monolith is homogeneous, and the inorganic 
matrix can be obtained essentially free of inorganic or organic 
impurities, e.g., less than 2 weight percent of impurities. 
A sol-gel derived porous glass monolith typically has a pore structure in 
which substantially all of the pores have diameters within about a 100 
angstrom diameter variation range, e.g., within a range between about 
50-150 or 300-400 or 900-1000 angstroms, as determined by sol-gel 
processing conditions. 
A sol-gel derived porous glass monolith can have exceptional optical 
properties because the inorganic matrix is homogeneous in chemical 
composition and physical structure. Since there is minimized light 
scattering, the sol-gel derived porous glass monolith exhibits excellent 
optical transparency and light transmitting ability. 
Nonlinear Optical Properties 
The fundamental concepts of nonlinear optics and their relationship to 
chemical structures can be expressed in terms of dipolar approximation 
with respect to the polarization induced in an atom or molecule by an 
external field. 
As summarized in the ACS Symposium series 233(1983) listed hereinabove in 
the Background Of The Invention section, the fundamental equation (1) 
below describes the change in dipole moment between the ground state 
.mu..sub.g and an excited state .mu..sub.e expressed as a power series of 
the electric field E which occurs upon interaction of such a field, as in 
the electric component of electromagnetic radiation, with a single 
molecule. The coefficient .alpha. is the familiar linear polarizability, 
.beta. and .gamma. are the quadratic and cubic hyperpolarizabilities, 
respectively. The coefficients for these hyperpolarizabilities are tensor 
quantities and therefore highly symmetry dependent. Odd order coefficients 
are nonvanishing for all structures on the molecular and unit cell level. 
The even order coefficients such as .beta. are zero for those structures 
having a center of inversion symmetry on the molecular and/or unit cell 
level. 
Equation (2) is identical with (1) except that it describes a macroscopic 
polarization, such as that arising from an array of molecules in a 
crystalline domain: 
EQU .DELTA..mu.=.mu..sub.e -.mu..sub.g =.alpha.E+.beta.EE+.gamma.EEE+...(1) 
EQU P=P.sub.O +.xi..sup.( 1)E+.xi..sup.( 2)EE+.mu..sup.( 3)EEE+...(2) 
Light waves passing through an array of molecules can interact with them to 
produce new waves. This interaction may be interpreted as resulting from a 
modulation in refractive index or alternatively as a nonlinearity of the 
polarization. Such interaction occurs most efficiently when certain phase 
matching conditions are met, requiring identical propagation speeds of the 
fundamental wave and the harmonic wave. 
A present invention nonlinear optical medium typically is optically 
transparent and exhibits hyperpolarization tensor properties such as third 
harmonic generation. 
These theoretical considerations are elaborated by Garito et al in chapter 
1 of the ACS Symposium Series 233 (1983); and by Lipscomb et al in J. 
Chem., Phys., 75, 1509 (1981), incorporated herein by reference. See also 
Lalama et al, Phys. Rev., A20, 1179 (1979); and Garito et al, Mol , Cryst. 
and Liq. Cryst., 106, 219 (1984); incorporated herein by reference. 
Nature of NLO Enhancement 
The level of response in an invention nonlinear optical medium is enhanced 
by molecular interactions between the NLO active compound and the 
complexing organic compound. The interactions may occur via electrostatic 
or donor-acceptor or Van Der Waals forces. 
While the precise mechanism of interaction has not been established, 
increased mobility of the NLO active molecules is a factor. The molecular 
interaction is evidenced by changes in chemical shifts of specific nuclear 
magnetic resonances arising from the NLO active organic compound or from 
nuclear magnetic resonances which derive from the complexing organic 
compound. 
Nonlinear optical response at a specific molar ratio of NLO active organic 
compound to thermoplastic polymer matrix in an invention solid solution is 
enhanced by the presence of the complexing organic compound, as compared 
to its NLO response in the absence of the complexing organic compound. 
The following examples are further illustrative of the present invention. 
The components and specific ingredients are presented as being typical, 
and various modifications can be derived in view of the foregoing 
disclosure within the scope of the invention.

EXAMPLE I 
This Example illustrates the preparation of organic solid solution optical 
media in accordance with the present invention. 
A reaction flask is charged with 80 grams of N,N-diethylmethacrylamide, 30 
grams of 4-N,N-dimethylamino-4'-nitrostilbene, and 0.1 gram of 
azo-bis-isobutyronitrile. The flask is purged with argon, then sealed and 
placed in a 60.degree. C. oil bath. 
The resultant product is an optically clear solid solution which exhibits 
third order nonlinear optical properties After a film sample of the solid 
solution is subjected to an electric field to form a stable configuration 
of aligned 4-N,N-dimethylamino-4-'-nitrostilbene molecules, it exhibits 
enhanced second order nonlinear optical properties. 
Solution state carbon-13 nucleus magnetic resonance spectroscopy indicates 
a 1:1 molecular ratio of N,N-diethylmethacrylamide and 
4-N,N-dimethylamino4'-nitrostilbene in the solution. An enhanced D C Kerr 
effect is observed by the procedures described in Example II, which 
correlates to a molecular association corresponding to a measured change 
in the chemical shift of nitor-carbon resonance. 
For comparative purposes, 80 grams of poly(N,N-diethylmethacrylamide) and 
30 grams of 4-N,N-dimethylamino-4'-nitrostilbene are admixed and heated to 
a homogeneous melt phase. On cooling, an optically transparent solid 
solution is formed. The solid solution does not exhibit any evidence of 
molecularly associated 4,4-N,N-dimethylamino-4'-nitrostilbene, and it 
exhibits a lower level of nonlinear optical response than the invention 
solid solution. 
EXAMPLE II 
This Example illustrates the preparation of an organic/inorganic composite 
composition in accordance with the present invention. 
A. GEL-DERIVED POROUS GLASSES 
Tetraethyl orthosilicate (TEOS), ethyl alcohol, water and 1,3,5-trioxane 
are mixed in a compositional mole ratio 1:4:4:0.85. Hydrofluoric acid (HF) 
solution is added (maintaining [HF]/[TEOS]=0.04) to the reaction mixture 
with vigorous stirring at 25.degree. C. After one hour, the solution is 
poured into plastic containers which then are tightly sealed. The samples 
are held at 25.degree. C. for 24 hours, during which time gelation occurs. 
The sealed containers are moved to a convection oven and heated at 
60.degree. C. for 24 hours. During the next 48 hours, the container lids 
are first loosened and then removed. 
When the samples show no further weight loss (about 36 hours), the oven 
temperature is raised and maintained at 100.degree. C. until again no 
further sample weight loss is observed (about 48 hours). At this point, 
the "xerogel" samples are transferred to quartz dishes and placed in a 
muffle furnace. From an initial temperature of 100.degree. C., the furnace 
temperature is increased to 600.degree. C. over a 24 hour period. The 
porous glass samples then are annealed from 600.degree. C. to 900.degree. 
C. for 25 hours at each 100.degree. C. increment. 
Analysis of the product glass samples indicates an average surface area of 
300 m.sup.2 /g, and a pore size distribution ranging between 50-60 
.degree. .ANG.. The porosity is determined to be 55% by the Archemedes 
method using ethanol as the saturating liquid. 
B. POLYMER AND SILICA GLASS-POLYMER COMPOSITES CONTAINING 
2-METHYL-4-NITROANILINE (MNA) 
The composites are prepared by in situ polymerization of methyl 
methacrylate (MMA) monomer solutions containing 2-methyl-4-nitroaniline 
(MNA). In the case of the glass-polymer systems, the gel-derived porous 
glass is imbibed with the monomer solution prior to polymerization. A 5 
wt% MNA-silica glass-PMMA composite is prepared in the following manner. 
In a 20 cc glass test tube (O.D.=1.5 cm), 0.61 g 2-methyl-nitroaniline and 
0.03 g of the free radial initiator, 2,2'-azobis(2-methylproprionitrile), 
are dissolved in 10.22 g methyl methacrylate. A cylindrical porous glass 
rod weighing 1.33 g (0.6 cm diameter.times.6.0 cm length), is fully 
immersed in the monomer solution containing MNA. When the porous glass is 
completely infiltrated, the test tube is sealed and the system is heated 
in an oil bath maintained at 38.degree. C. After 24 hours, the 
polymerization of MMA results in a transparent composite showing minimum 
birefringence. The system then is cured at 38.degree. C. over a 48 hour 
period. 
C. SAMPLE FABRICATION 
Poly(ethylene glycol) average M.W. 200-600 (Aldrich) is employed as a 
lubricant in all cutting and polishing operations. For DC Kerr 
experiments, composites are cut in slab form (i.e., 1.5 cm.times.2.5 
cm.times.0.3 cm) and the two faces perpendicular to the laser beam pathway 
are polished. 
D. DC KERR MEASUREMENTS 
A detailed description of the experimental set-up is published in Proc. 
SPIE, 682, 153(1986). 
A typical experiment is conducted by increasing the voltage across a sample 
and measuring it with a high voltage probe. At the same time, the 
resultant change in intensity of the laser beam passing through the sample 
is measured with a lock-in amplifier. For the Kerr effect, one obtains a 
linear plot of intensity (I) versus voltage squared (V.sup.2). A cell 
containing CS.sub.2 is placed in the optical train as a reference, and a 
plot of I versus V.sup.2 for this reference is also generated. The ratio 
of the slopes of the unknown to the reference gives the Kerr constant of 
the unknown material relative to CS.sub.2. 
E. ELECTRO-OPTICAL DC KERR EFFECTS 
The electro-optic effect is the change in the index of refraction of a 
medium when an electric field is applied across it. The linear change of 
refractive index with an applied field (i.e., Pockels effect) occurs in 
noncentrosymmetric media, while the quadratic dependence is called the 
Kerr effect and occurs in all media. 
The birefringence, .DELTA.n, induced in a Kerr composite is 
EQU .DELTA.n=.lambda.BE.sup.2 
where B is the Kerr constant; .lambda. is the wavelength of light; n is the 
refractive index; and E is the applied electric field. 
When a molecule is dissolved in a host medium such as PMMA or silica 
glass-PMMA, one measures the incremental Kerr constant, .DELTA.B, where 
.DELTA.B=B(solution)-B(host medium). When the molecule is totally free to 
orient in the applied field, as in solutions, one can define a molar Kerr 
constant, mK. This constant is essentially the product of the dipole 
moment squared and the optical anisotropy of the molecule. For an 
unhindered molecule in solution, the largest contribution to mK is due to 
molecular orientation resulting from the coupling of the electric field 
with the permanent and induced dipole moments of the molecule. This is the 
primary mechanism for the induced birefringence, and reveals the optical 
anisotropy of the molecule. Weaker contributions also arise from the 
distortion of the electronic cloud of the molecule in the electric field; 
however, these are negligible in the DC Kerr effect. 
In the case of a solid solution such as MNA in PMMA or in glass-PMMA, the 
interpretation of mK is more complicated since the molecule is not totally 
free to move in an electric field. However, the mK value still can be used 
as a measure of the relative freedom of a solute molecule in a solid 
medium. 
The effective molar Kerr constant for MNA in PMMA is determined to be 
1.32.times.10.sup.-9 esu, while that for MNA in glass-PMMA is estimated to 
be 1.65.times.10.sup.-9 esu. For MNA in a dioxane solution, the mK value 
is found to be 6.85.times.10.sup.-9 esu. Calculating values of 
mK(composite)/mK(dioxane solution), one obtains ratios equal to 0.19 and 
0.24 for the PMMA and glass-PMMA systems, respectively. In both 
composites, the freedom of MNA to orient in the electric field is reduced 
relative to that in solution, although it appears the MNA is slightly more 
mobile in the glass-polymer host than in PMMA alone.