Compositions – Light transmission modifying compositions
Reexamination Certificate
2000-06-23
2002-12-31
Dawson, Robert (Department: 1712)
Compositions
Light transmission modifying compositions
C385S005000, C556S008000, C568S004000, C568S003000, C585S024000, C252S587000, C252S588000, C252S589000
Reexamination Certificate
active
06500363
ABSTRACT:
BACKGROUND OF THE INVENTION
A critical aspect of the field of nonlinear optics (NLO) is focused upon the response of materials to electromagnetic fields. Interest often relates to how materials generate new electromagnetic fields with altered properties, such as frequency and phase, upon irradiation with an external electromagnetic field. Materials efficient at nonlinear photonic signal manipulation are of interest for a large number of technological applications including optical communications and computation, optical switching and limiting, data storage and retrieval, and dynamic image processing, among numerous others. (Prasad, P. R. and Williams, D. J.
Introduction to Nonlinear Optical Effects in Molecules and Polymers;
John Wiley and Sons: New York, 1991.) One of the primary limitations encountered, however, is the availability of suitable materials with large nonlinear responses. Most molecular nonlinear optical materials are inefficient photonic modulators. Major research initiatives have, therefore, been directed both toward gaining a detailed understanding of fundamental structure-optical property relationships and the theoretical modeling, experimental synthesis and NLO property measurement of new materials. A great deal of computational and experimental work, primarily with organic systems, has begun to address these important relationships. The present invention relates to the use of new classes of compounds as nonlinear optical materials.
Molecular NLO materials have many particularly attractive properties including ultrafast response times, lower dielectric constants, significantly improved processability, facile three dimensional design capabilities, and greatly enhanced NLO responses. (Blau, W.
Phys. Technol.
1987, 18, 250.) Most molecular NLO materials, for example, employ electron donating (donors) and withdrawing groups (acceptors) connected through an organic framework (bridge), although several metalloorganic systems have also been explored. (Cummings, S. D., Cheng, L.-T. and Eisenberg, R.
Chem. Mater.
1997, 9,440.)
The design and optimization of new NLO materials has primarily involved addressing what chemical factors affect the molecular hyperpolarizabilities of the material. For example, the most commonly employed model for understanding the fundamental relationships between the second-order responses (&bgr;) and molecular structure is the two-state model. (Oudar, J. L.
J. Chem. Phys.
1977, 67, 446.) In qualitative terms, when the electric field component of a moderate strength incident electromagnetic wave interacts with a compound, a linear electronic polarization occurs within the compound due to photon-electron interactions. The incident oscillating electric field causes an oscillating dipole to be generated in the chromophore proportional to the applied field strength. At high incident field strength, however, the induced electronic polarization becomes nonlinear, ultimately leading to second, third, etc. harmonic generation. A power series expansion has been used to describe the nonlinear behavior of the induced polarization. In rigorously centrosymmetric chromophores, the second-order response is zero since only odd terms of the power series expansion are allowed. Molecular parameters which enhance a noncentrosymmetric electronic polarization in the compound, therefore, enhance its second-order response. For organic NLO materials involving electron donating and withdrawing groups (often referred to as “push-pull” systems), the value of &bgr; is primarily dictated by the intramolecular charge polarization, the transfer integral and the excited state of the compound. The two-state model assumes that the large second-order response (&bgr;) is due primarily to an intramolecular charge-transfer interaction between the acceptor and donor portions of the material. The overall value of &bgr; is given by the sum of an additive portion (&bgr;
add
) and a charge transfer portion (&bgr;
ct
). The additive portion (&bgr;
add
) accounts for the interactions between the individual substituents and the organic framework. The dominant intramolecular electronic redistribution, or charge transfer contribution (&bgr;
ct
), is given by:
β
CT
=
12
π
2
h
2
ω
max
(
ω
max
2
-
4
ω
2
)
(
ω
max
2
-
ω
2
)
η
ge
2
Δ
μ
(where &ohgr;
max
is the absorption band maximum, &ohgr; is the frequency of the applied electric field, &mgr;
ge
is the transition dipole moment between the ground and lowest frequency excited state, and &Dgr;&mgr; is the difference between the dipole moment of the ground and excited states). The two state model is a somewhat oversimplified description but it has been shown to be particularly useful in understanding the nonlinear optical properties of many molecular systems. Thus, in the “push-pull” organic compounds, increasing the length of the &pgr;-conjugated pathway between the donating and withdrawing groups and increasing the donor/acceptor group strengths typically leads to an increase in the observed electronic molecular hyperpolarizabilities. Increasing the length of the &pgr;-framework, however, also usually leads to a bathochromic shift of the intramolecular charge transfer absorption, typically into the visible region, which often limits the usefulness of the these materials. The calculated second-order responses for twisted &pgr;-chromophores, however, have been recently shown to be unresponsive toward the typical strategies for increasing &bgr;, such as by increasing both the length of the &pgr;-conjugation and the donor and acceptor strengths. This is primarily because the second-order responses for these twisted compounds are most dependent upon factors which effectively bring about and ultimately stabilize intramolecular charge separation. (Albert, I. D. L., Marks, T. J. and Ratner, M. A.
J. Am. Chem. Soc.
1998, 120, 11174.).
The numeric values for &bgr; range over six orders of magnitude, typically from about 0.001 for very small compounds to nearly 1000 (×10
−30
cm
5
esu
−1
) for the best extended &pgr;-conjugated systems. Values of 10 to 100 (at 0.65 eV) are usually considered large and between 100 and 1000 (×10
−30
cm
5
esu
−1
) exceptionally large. It is important to observe, however, that the magnitude of &bgr; is rather sensitive to the frequency of the electromagnetic radiation employed and generally increases significantly with increasing excitation energy. In addition, these qualitative descriptions do not apply at near resonant frequencies. (Kanis, D. R., Ratner, M. A. and Marks, T.
J. Chem. Rev.
1994, 94, 195). Table 1 gives several example molecular hyperpolarizabilities for known high &bgr; NLO systems.
TABLE 1
Calculated and measured second-order responses (&bgr;) at
1.17 eV for selected high &bgr; NLO compounds
(aniline and nitrobenzene shown for comparison)
a
Compound
&bgr;
calc'd
b
&bgr;
expir.
1.84
0.79-2.46
4.55
1.97-4.6
34.4
16.2-34.5
213.1
180-260
466.8
470-790
30.8
a
The values of &bgr; are reported in units of 10
−30
cm
5
esu
−1
.
b
Calculations are based upon the Pariser-Parr-Pople model.
24
Calculational methods have been used to great effect in studying the relationships between nonlinear responses and molecular architectures. Numerous methods have been extensively and effectively employed including semiempirical methods (MOPAC and ZINDO principally), density functional theory (DFT) and ab initio methods. Significant advantages in calculational speed have been particularly realized by employing semiempirical methods (such as MOPAC AM1) which apparently retain the NLO calculational accuracy obtained with higher order ab initio basis sets (such as 6-31 G* *). Where experimental data exists, exceptionally good agreement is generally obtained between the calculated and experimental values of &bgr; as illustrated in Table 1.
OBJECTS OF THE INVENTION
A key component of research in NLO systems has involved the discovery of new materials effici
Allis Damian G.
Spencer James T.
Dawson Robert
Peng Kuo Liang
Syracuse University
Wall Marjama & Bilinski LLP
LandOfFree
Classes of high linear and nonlinear response compounds does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Classes of high linear and nonlinear response compounds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Classes of high linear and nonlinear response compounds will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2997589