Angular-dependent photoselection and anisotropy of optical absorption for photochromic molecules in glassy poly(methyl methacrylate)

It is shown that films of poly(methyl methacrylate) which contain the thermally-stable photochrome 7,7a-dihydro-2,4,7,7,7a-pentamethylbenzo-[b]-furan-5,6-dicarboxylic anhydride II may be rendered optically dichroic using polarized laser light (λ = 514·5nm). The dichroism is produced by angular-dependent photoselection of photochromic molecules in the photoconversion of photochrome II to fulgide I. The absorption anisotropy has been measured as a function of the angle between the planes of polarization of the pump and probe beams, and it is found to be time-invariant for this photochrome/glassy polymer system at room temperature. It is suggested that the time-dependence of absorption anisotropy of thermally-stable photochromic molecules in host polymer or liquid media should provide a direct means of studying their reorientational motions, and should be applicable over the time-range 10-11 to 10+3 s.

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