Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-05-19
2003-05-20
Gerstl, Robert (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C548S444000, C549S031000
Reexamination Certificate
active
06566529
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to materials exhibiting strong two-photon absorption that has optical power limiting property which property is particularly useful for protection of human eyes and sensitive photodetectors.
2. Description of Related Art
Non-linear optical materials exhibiting two-photon absorption cross section have drawn growing attention recently due to the unique feature that the two-photon absorption, in the presence of intense laser pulses, is capable of creating excited states with photon of half the normal excitation energy and this allows an enhanced penetration into absorbing media. Thus, two-photon absorption materials with a large cross section value &sgr; have a variety of application areas, particularly as in optical power limiters.
A number of recent compounds or chromophores, including commercial dyes, display two-photon absorption but they have relatively small cross section values. Unfortunately, design criteria for molecules with large cross section values have not been developed.
A design strategy developed recently is based on the molecules consisting of a three-component system with a unique heteroaromatic &pgr; center which is linked symmetrically or asymmetrically through conjugation by electron donors D or electron acceptors A, resulting in products D-c-D, or D-c-A or A-c-A, where c represents the &pgr; center group. It is claimed that the cross section value &sgr; can be enhanced by increasing the conjugation length, D/A strength and molecular symmetry that enhance the electronic redistribution from the electron donor ends D of the molecule to the center c, or vice versa, resulting in a large increase of the cross section value &sgr; and the shift of the two-photon absorption peak to the longer wavelengths. In particular, when the &pgr; center c portion of the molecule has an electron-deficient substituent, D-c-D molecules become more effective.
On the other hand, one notable compound developed by the Air Force Lab, i.e., AF-50, and is known as a benchmark of cross section &sgr;, has an asymmetric structure D-c-A where D is diphenylamine group, c is 9-dialkylfluorenyl and A is 4-ethenylpyridine. This structural formula of the AF-50 product is as follows:
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
An object of this invention is materials or compounds based on dithienylthiophene (DTT) or derivatives thereof which have the two-photon absorption property characterized by up energy conversion.
Another object of this invention is compounds containing dithienylthiophene or a derivative thereof having attached at its ends an electron donor or an electron acceptor.
Another object of this invention is compounds containing dithienylthiophene or its derivatives having attached at its ends electron donors or electron donors and electron acceptors, the compounds having a two-photon absorption property.
Another object of this invention is compounds based on dithienylthiophene or its derivatives having attached at its ends an electron donor or an electron acceptor and having a two-photon absorption property.
Another object of this invention is compounds containing dithienylthiophene or its derivatives the &pgr; center having attached at its ends electron donors and/or electron acceptors, and the compounds having two-photon absorption property with cross section value &sgr; being in excess of about 3×10
−46
cm
4
sec when measured at 8 ns pulse duration.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to novel organic oligomeric chromophore compounds having an outstanding nonlinear optical property of two-photon absorption. The compounds of this invention are based on dithienylthiophene or a derivative thereof having attached thereto electron donors and/or electron acceptors. These compounds exhibit greater two-photon absorption cross section &sgr; values so that a variety of applications are expected in areas such as two-photon excited fluorescence microscopy, optical limiting, three-dimensional optical data, storage, and two-photon induced caging studies. The compounds of this invention are soluble in common organic solvents, thermally stable and form optical quality films when cast from solutions. Also, these compounds are compatible with many organic polymers and dyes, forming optical quality thin films of blends free of phase separation.
The novel compounds of this invention contain a &pgr; center based on dithienylthiophene and are conjugated. Such compounds have an outstanding nonlinear optical property of two-photon absorption as determined by cross section value &sgr; (sigma).
The compounds of this invention having the two-photon absorption property can generally be represented as
Y
1
-R
1
-c-R
2
-Y
2
where Y
1
and Y
2
are individually selected from substituted or unsubstituted electron donors and electron acceptors, R
1
and R
2
are individually selected from conjugated hydrocarbon linkages and bonds, and c is a substituted or unsubstituted &pgr; center based on dithienylthiophene or its derivatives. In a preferred embodiment, the compounds are conjugated; both Y groups are electron donors or one Y group is an electron donor and the other is electron acceptor; the R groups are ethylene linkages each containing 2-6 carbon atoms; and the center c is a &pgr; center based on dithienlthiophene or its derivative. More specifically, the compounds of this invention can be depicted as follows:
D
1
-R
1
-c-R
2
-D
2
(or A)
where D
1
and D
2
are individually selected from substituted or unsubstituted electron donor groups, R
1
and R
2
are individually selected from substituted or unsubstituted ethylenic linking groups, c is substituted or unsubstituted &pgr; center group based on DTT and A is a substituted or unsubstituted electron acceptor group. Suitable substituents are groups that do not adversely affect the two-photon absorption property of the compounds and include alkyl groups of C
1
-C
16
carbon atoms, particularly at positions 3 and 3′ on the dithienylthiophene group.
In an especially preferred embodiment the compounds of this invention include oligomeric solid compounds 101, 102, 103 and 104, depicted below:
In the compounds 101, i.e., 2,6-bis[2-(9-ethylcarbazol-3-yl)vinyl]thiopheno[3′,2′-2,3]thiopheno[4,5-b]thiophene; 102, i.e., 2-[2-(4-{5-[4-(tert-butyl)phenyl](1,3,4-oxadiazol-2-yl)}phenyl)vinyl]-6-[2-(9-ethylcarbazol-3-yl)vinyl]thiopheno[3′,2′-2,3]theopheno[4,5-b]thiophene; 103, i.e., {4-[2-(6-{2-[4-(diphenylamino)phenyl]vinyl}thiopheno[2′,3′-4,5]thiopheno[3,2-b]thiophen-2-yl)vinyl]phenyl}diphenylamine; and 104, i.e., [4-(2-{6-[2-(4-{5-[4-(tert-butyl)phenyl](1,3,4-oxadiazol-2-yl)}phenyl)vinyl]thiopheno[2′,3′,-4,5]thiopheno[3, 2-b}thiophen-2-yl}vinyl)phenyl]diphenylamine; depicted above, the central DTT group is attached through conjugation to either an electron donor at both ends or an electron donor at one end and an electron acceptor at the other end, forming symmetrical compounds 101 and 103 or unsymmetrical compounds 102 and 104. As used herein, “D” denotes an electron donor group, “c” denotes the DTT group &pgr; centrer, and “A” denotes an electron acceptor group. The electron donor groups and the electron acceptor groups are connected to the central DTT-based &pgr; center by means of ethylenic linkage —CH═CH—. In a preferred embodiment, D is a carbazole or a triphenylamine group and A is a 2-mono or diparyl-5-(4-ter-butyl)-1,3, 4-oxadiazole group.
Compounds of this invention can be synthesized by the Wittig reaction of a dithienyldthiophene dicarboxaldehyde with a triphenylphosphonium functional end of D or A group. Ultrapure products can be obtained through exhaustive purficiations by column chromatography and confirmed by NMR, electronic spectrum and elemental analysis.
As
Kim Kie-Soo
Kim Oh-Kil
Lee Kwang-Sup
Woo Han Young
Gerstl Robert
Kap George A.
Karasek John J.
The United States of America as represented by the Secretary of
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