Solid polymeric matrices containing rhodamines and their use...

Details Solid polymeric matrices containing rhodamines and their use... Solid polymeric matrices containing rhodamines and their use...

1997-06-12

2001-08-28

Krass, Frederick (Department: 1614)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S268000, C526S292300, C526S328000, C526S328500, C525S329900, C525S330100, C525S330500, C008S648000, C204S157150, C204S157410, C204S157610

Reexamination Certificate

active

06281315

ABSTRACT:

Dye lasers are profusely applied in very different fields. For example, they are used every day more and more in Medicine for the selective destruction of tissue, by means of the so called photodynamic therapy, and for the “in situ” diagnosis of possible tumours. However, both in the industrial field and in their medical applications, the employment of dye lasers implies the use of dyes in solutions, which signifies a series of disadvantages and limitations, which are: the employment of organic solvents, some of which are toxic and volatile, the maintenance of a constant flow of the dye solution within the cavity of the laser; and other tedious operations, such as having to renew the dye solution, or else replace it when a change of spectral region of the emittance of the laser is desired. For this, the availability of solid dye lasers, with notable advantages over liquid lasers is of great technical interest, since besides being more compact with a notable decrease in its size, it allows working in the absence of solvents, a particularly important aspect during its clinical use, and also, with a minimum maintenance, capable of changing the spectal interval of the laser emittance in a rapid and simple manner. Other additional advantages derived from the use of a solid dye laser are, the freedom of design of the cavity and the low cost of the same when the solid is a polymer.
A laser is a luminous source, the light of which, monochromatic and coherente, originates from the emittance stimulated by the radiation of a material. As its name indicates, the stimulated emittance is the one which is caused by the disactivation of previously excited conditions caused by the actual radiation emitted by the material. If said material is a fluorescent colorant, the laser is called of dye. Attending to the energetic levels implied by the laser emittance, the dye lasers may be considered as four level lasers.
The basic operational mechanism of a dye laser is herewith described. If a dye solution for laser is illuminated with light with a wave length which falls within its absorption band (pumping radiation), the molecules of said dye are excited from the fundamental level singlet S
o
up to some rotovibrational level of the first excited singlet condition S
i
. Due to collisions with other molecules, the excess of rotovibrational energy is rapidly dissipated in the form of heat, and so, the molecule relaxes to a rotovibrational level below S
1
. In S1 condition, the molecule may emit spontaneous fluorescent radiation, passing to any rotovibrational level of fundamental conditionl S
o
. Finally, relaxation non radioactive processes carry the molecule to rotovibrational level zero from fundamental condition. The light emitted has always a wave length which is longer than that of the pumping radiation, due to the fact that part of the excitment energy is dissipated by non radioactive processes. If the dye is excited at the second excitment singlet, or level S
2
, or at other higher levels, the molecule may decline by non radioactive processes to condition S
1
. If the intensity of the pumping radiation is sufficiently high, for example 100 kw/cm
2
, it may be achieved that the number of molecules in excited condition S
1
be superior at all times to that of the molecule in fundamental condition S
o
(population reversal), the stimulated emittance or laser being then possible throughout all the fluorescent band, with the exception of the part which overlaps with the absorption band.
STATE OF THE ART
The dyes available for use as a source of laser radiation, obtained by organic synthesis, over a wide spectral zone, from 340 nm (stilbenes) up to 1200 nm (cyanines), all present high monochromaticity in the emittance and the majority operate as has just been described. In the practical application of this type of dyes two limiting factors exist: a) the photostability, since the dyes must support very high pumping energies and a prolonged exposure to radiation, which may cause its degrading, losing effectivity as emitting sources; and b) syntonization interval since the majority of the normal dyes have only small wave length intervals in which the the laser efficiency is acceptable.
The use of a laser dye solution in a solid medium has evident technical advantages as regards the use of a liquid medium; the sample is more manageable and attainable, generally of low density, easily machinable, etc. The stimulated emittance generated by Rhodamine G dispersed in poly(methyl methacrylate) was described for the first time in 1967 by Söffer and McFarland [
Appl. Phys. Lett.
10, 266(1967)] and the stimulated emittance of rhodamines B and 6G dispersed in the same polymer was described a year later by Peterson and Snavely [
Appl Phys. Lett
12 238(1968)]. Since then, a great variety of solid matrices have been described (polycarbonates, polystyrene, polyvinylalcoholes and polyacrylates) in which diverse types of dyes have been dispersed.
However, due to the generally scarce resistance of the polymeric matrix to strong pumping radiations, as well as to the generally low thermal stability of the dyes, its extensive use has been impossible up to the present. None the less, the work carried out by O'Conell and col.[
Opt. Eng.
22 393(1983)] indicates that the duly purified poly(methyl methacrylate) is a polymer which is resistant to intense radiation. Another additional difficulty lies in the low solubility of the laser dyes, developed up to this moment in the majority of conventional polymers. In fact, in the described examples in the literature, the dye is not to be found really disolved but in the majority of the cases, dispersed in the matrix.
A detailed description of the state of the art has been recently published by our working group [R. Sastre, A.Costela,
Adv. Mater.
7, 198 (1995)]. In reality, our working group has managed to obtain laser emittance, with reasonable efficacy and an incremented photostability as regards previous works, with real solutions of Rhodamine 6G dye and Rhodamine 640 dye in polymeric matrices (poly (methyl methacrylate), poly (methacrylate 2-hydroxyethyl)) [F.Amat Guerri, A.Costela, J. M.Figuera, F.Florido, I.García-Moreno and R.Sastre,
Opt. Commun.
114, 442 (1995), R.Sastre and A.Costela,
Adv. Mater.
7 198(1995); A.Costela, F.Florido, I. García-Moreno, R Duchowicz, F.Amat Guerri, J. M.Figuera and R. Sastre,
Appl. Phys. B,
60, 383 (1995)].
The only works (including a registered patent) on solid materials for dye lasers in which the dye is to be found in covalent anchorage with a polymeric matrix, has been published by our group. With other purposes, especially the photostablization of solid polymers, polyers have been described in which a chromophore with an ethylenic substitute has been introduced in the polymeric chain by copolymerization. Used as monomers in said works with a different purpose were among others, acrylates, styrene and vinyl chloride [F. A.Bottino, G.Di Pascuale and A.Pollicino,
Macromolec
23,2662(1990); K. P.Ghiggino, A. D.Saully, S. W.Biggen and M. D.Yandell,
J.Polym, Sci. Part C; Polym. Lett
26, 505(1988); D. B.O'Connor, G. W.Scott, D. R.Coulter, A.Gupta, S. P.Webb, S. W.Yeh and J. H.Clark,
Chem.Phys. Lett
121,417(1985)].
DESCRIPTION OF THE INVENTION
The present invention is based on the use of a series of dyes with a common structure; the xanthene skeleton substituted by phenyl in position 9, and which in position 2′ of said phenyl, possesses a group of esterified carboxyl by an R group with an unsaturation which may be polymerized.
The introduction of the unsaturated R group in the dye molecule is preferably carried out by a reaction between a Rhodamine having a free carboxyl group in position 2′(R═H), and an unsaturated halogenated derivative, performing the reaction in the presence of a base, such as anhydrid solid carbonate. The reaction between carboxylic acid salts and halogenated derivatives, especially allylics or benzylics is well known as a manne

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