Preparation of Thin Film Phthalocyanine Glasses for Optical Limiting
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R. D. George, A. W. Snow, J. S. Shirk, S. R. Flom, and R. G. S. Pong Naval Research Laboratory, Washington, DC 20375. ABSTRACT To explore the use of phthalocyanine materials as a solid-state component in an optical limiter, the issues of morphology, film processing and optical limiter activity/stability are investigated. Metal-free and lead phthalocyanine films with glassy morphologies are obtained by chemically functionalizing the ring periphery with an amine-epoxy substitution. Uniform films were obtained by a shearing technique. Comparative optical measurements are made on the amineepoxy lead phthalocyanine compound as a concentrated solution and as a glassy thin film. Both the solution and film are reverse saturable absorbers at 590 nm. The concentrated solution is a very effective optical limiter. The glassy thin film is susceptible to damage (cavitation caused by the incident beam) and performs comparably only at low incident energies. A liquid matrix may have the benefit of self-healing such damage. INTRODUCTION In the development of phthalocyanine materials for use as the active component in an optical limiting device we are attempting to progress from liquid solutions to solid-state films. This would have the obvious advantage of being a single component substance with a physical form that does not require encapsulation to contain flow. Three important materials issues arise when undertaking this development. First is the formation of aggregates which become anisotropic scattering centers in the solid-state [1,2] and cause unacceptable scattering for an optical limiting device. We address this issue by employing peripheral phthalocyanine substitution that promotes an organic glass morphology. Second is the processing of this material into a uniform thin film of controlled thickness. Third is the optical limiting activity and stability in the solid-state compared with that in the liquid solution. Solutions of lead phthalocyanine compounds have
been reported to display useful optical limiting properties [4,5], and for the reason above it is of particular interest to develop these properties in the solid-state. This paper describes our efforts at addressing the above three issues. SYNTHESIS AND PHYSICAL PROPERTIES
The chemical structure of the glassy metal-free (H2Pc(PGEAp)4) and lead phthalocyanines (PbPc(PGE3Ap)4) used in this study is illustrated below.
M = H2 , Pb
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Mat. Res. Soc. Symp. Proc. Vol. 374 ©1995 Materials Research Society
Synthesis of the metal-free phthalocyanine from 4-nitrophthalonitrile, 3-aminophenol and phenylglycidyl ether has been described previously [6]. The PbPc(PGE3Ap), is subsequently
prepared from H2Pc(PGEAp) 4 by treatment with lead acetylacetonate. These glassy phthalocyanines have several features of irregular symmetry which inhibit crystallization and/or long range molecular order. These include a mixed geometrical isomer substitution at either of the outer benzo positions of the phthalocyanine structure, a meta as opposed to para substitution of the aminophenoxy st
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