Metallo-porphyrins

Details Metallo-porphyrins Metallo-porphyrins

1999-12-22

2001-05-22

Gerstl, Robert (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

Reexamination Certificate

active

06235895

ABSTRACT:

It is known that porphyrins with meso-alkynyl substituents have nonlinear optical properties. That is to say, at certain wavelengths, the excited state absorption cross-section &sgr;
ex
of the porphyrin is larger than the ground state absorption cross-section, &sgr;
gr
. Therefore the absorption of a sample increases strongly with increasing radiation intensity as the excited state population develops. This property is useful for a variety of electro-optic applications. In addition, the porphyrins described have other important physical properties that make them attractive, they are stable, cheap to produce and are highly soluble in organic solvents. The last property means that they can be used either in a liquid device or in a thin film (e.g. the polymer PMMA).
To be of practical interest, the porphyrin derivative needs to show strong nonlinear absorption properties at wavelengths at or close to those of commonly available lasers, i.e. the ratio &sgr;
ex
/&sgr;
gr
must be large at the specific wavelength of interest. The most commonly used wavelength in the visible region is 532 nm, which corresponds to the frequency doubled wavelength of Nd:YAG, which operates at 1064 nm. Previous studies, by us, on the porphyrin class of materials has shown that the largest excited state absorption coefficient, &sgr;
ex
(max) occurs at a wavelength slightly longer than that corresponding to the maximum linear absorption, &sgr;
gr
(max). In the compounds described here we have engineered the structure, through the degree of conjugation and the central metal atom, such that &sgr;
gr
(max) is at a wavelength slightly less than 532 nm (i.e. typically 500 nm). Most porphyrin compounds exhibit a &sgr;
gr
(max) at wavelengths significantly less than 500 nm. We have also engineered the molecular structure such that the spectral bandwidth of the linear absorption peak is narrow. This is achieved by designing a rigid and symmetric molecular structure. The narrow bandwidth is crucial since it allows &sgr;
gr
(max) to be positioned close to 532 nm without drastically increasing the value of &sgr;
gr
at 532 nm. Using these techniques we have been able to maximise the ratio of &sgr;
ex
/&sgr;
gr
at 532 nm.
Having optimised the molecular design and synthesis a number of applications become apparent:
1) The porphyrin sample in either liquid or solid format can be used to change the shape of a Q-switched (nanosecond duration) laser pulse at 532 nm. The tail of the pulse will be severely attenuated as the excited state population accumulates. This will result in a drastic reduction in the laser pulse duration.
2) The energy transmitted through the porphyrin sample in either a liquid or solid format will be reduced, and the reduction will depend on the initial pulse energy. This effect can be used to dampen pulse-to-pulse fluctuations in energy, i.e. the material could be used to stabilise the energy and prevent damage to subsequent optical components.
This invention provides compounds having formula (I) or (II).
These are monomeric or oligomeric metallo-porphyrin derivatives having meso-alkynl substituents. They are characterised by the fact that the metal atom M is Pb or Sn or Bi. As is demonstrated in the experimental section below, Pb has the effect, compared to the underivatised H form of the porphyrin, of increasing an absorption wavelength by some 40-50 nm. This increase is technically important. It is expected that Sn and Bi will show the same effect.
Substituents are possible on any or all of the twelve ring carbon atoms. The following references describe porphyrins with various ring substituents:
1. Meso-alkynyl porphyrins, H L Anderson, Tetrahedron Lett. 1992, 33, 1101-1103.
2. Conjugated porphyrin ladders, H L Anderson, Inorg. Chem. 1994, 33, 972-981.
3. Synthesis and third order nonlinear optical properties of a conjugated porphyrin polymer, H L Anderson, S J Martin and D D C Bradley, Angew. Chem. Int. Ed/. Engi, 1994, 33, 655-657.
4. Photophysical and transport properties of a novel soluble conjugated polymer based on zinc-porphyrin units edge-linked with acetylenic spacers, K Pichler, H L Anderson, D D C Bradley, R H Friend, P J Hamer, M G Harrison, C P Jarrett, S J Martin and J A Stephens, Mol. Cryst. Liq. Cryst. 1994, 256, 414-422.
5. Supramolecular orientation of conjugated porphyrin oligomers in stretched polymers, H L Anderson, Adv. Mater. 1994, 6, 834-836.
6
. Assembly and crystal structure of a photoactive array of five porphyrins, S Anderson, H L Anderson, A Bashall, M McPartlin and J K M Sanders, Angew. Chem. Int. Ed. Engl. 1995, 34, 1096-1099.
7. Femtosecond transient photoinduced transmission measurements on a novel conjugated zinc porphyrin system, G E O'Keefe, G J Denton, E J Harvey, R T Phillips, R H Friend and H L Anderson, J. Chem. Phys. 1996, 104, 805-811.
8. WO 94/04614 (The Trustees of the University of Pennsylvania).
Unsaturated ring substituents may be chosen to make the compound rigid and flat or other desired shape; or to enlarge or modify the conjugated unsaturation system; and thereby to modify the absorption wavelengths. Saturated substituents may be chosen to promote stability or solubility in desired organic solvents or in plastics materials. The knowledge in the art is sufficient to enable a skilled reader to play about with ring substituents in this way. So the following indications are intended to be guidelines rather than rigid definitions.
The compounds are shown as monomers (when n=1) and also as oligomers (when n=2-20). Skilled workers in the field are able to make porphyrin monomers and to join them into chains and rings and networks. These oligomers may have altered and beneficial non-linear absorption properties.
The indications are:
each R
1
is independently —SiR
3
or R or —CCSiR
3
or —CCR or H,
each R
2
is independently —CCSiR
3
or —CCR or H,
each X is independently H or C
1
to C
2
, hydrocarbyl optionally including a carboxylic acid or ester group,
each Y is independently H or C
1
to C
20
hydrocarbyl,
each R is independently H or C
1
to C
20
hydrocarbyl,
Z is C
1
to C
20
alkylene or arylene.
The following examples illustrate the invention and are described with reference to reaction schemes 1, 2, 3 and 4.
The compounds may be electrically neutral or cationic or anionic. The nature of any counter-ion is not material to the invention.
EXAMPLE 1
Experimental Details for Preparation of Lead and Tin Porphyrins
4-Butyl-(trimethylsilylethynyl)benzene (2)
Trimethylsilylacetylene (3.6 ml, 26 mmol) was added to an oxygen-free mixture of 4-bromo-butylbenzene 1 (5.0 g, 24 mmol), Pd(OAc)
2
(105 mg, 470 &mgr;mol.), PPh
3
(246 mg, 940 &mgr;mol) and Cul (45 mg, 235 &mgr;mol) in triethylamine (10 ml) under nitrogen. The mixture was refluxed for 5 h and the triethylamine hydrogen bromide and colloidal palladium produced removed by flash-chromatography (SiO
2
/60-80 pet. ether). The product was distilled at reduced pressure; unreacted 4-bromo-butylbenzene came over at 44-50° C./0.15 mmHg (yield 1.0 ml) and the product was collected at 73-83° C./0.20 mmHg. Yield 3.094 g (57% or 77% based on recovered starting material). &rgr; 0.876 g/ml; &dgr;
H
(CDCl
3
, 200 MHz) 7.40 (2H, d, J=8 Hz), 7.13 (2H, d, J=8 Hz), 2.62 (2H, t), 1.60 (2H, m), 1.35 (2H, m), 0.93 (3H, t), 0.26 (9H, s); &dgr;
c
(CDCl
3
, 50 MHz) 143.8, 132.1,128.5,120.4,105.6, 93.3, 35.5, 33.3, 22.2,13.8, −6.9; m/z (GCMS, El) 231.
4-Butlyphenylpropynal (3)
A solution of MeLi.LiBr (1.5M in Et
2
O; 6.25 ml, 9.38 mmol) was added to an oxygen-free solution of 4-butyl-(trimethylsilylethynyl)benzene 2 (2.3 ml, 9.4 mmol) in tetrahydrofuran (10 ml) under N
2
. After 2 h the mixture was cooled to −25° C. and dry N,N-dimethylformamide (2.0 ml, 26 mmol) was added. The mixture was stirred for 1 h then poured onto 5% aqueous H
2
SO
4
(150 ml) at 0° C. The product was extracted with dichloromethane, dried over MgSO
4
and distilled under reduced pressure collecting the fraction boiling at 81-93° C. at 0.15 mmHg. Yield 1.1789 (67%). &rgr; 0.947 g/ml; &dgr;
H
(CDCl
3

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