29 November 2000 Photo-orientation movement of photoisomerizable chromophores: quantifying analytical theory and application to spectrally overlapping and distinguishable isomers
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Abstract
We introduce the analytical theory of couples photoisomerization and photo-orientation both for individualizable and spectrally overlapping isomers, and we use it to quantify the photo-orientation movement of chromophores in polymers including photoisomerization quantum yields. We study photo-orientation processes in A - B photoisomerizable systems where B is unknown. We contrast systems where the isomers are individualizable and without thermal A implied by B isomerization, namely diarylethene and spiropyran-type chromophores in films of poly-methyl- methacrylate, respectively, and systems of nondistinguishable isomers, namely push-pull azobenzenes attached to polyurethane polymers. When diarylethene and spiropyrans are oriented by polarized excitation, the apparent optical orientation changes sign for the ultra- violet versus the visible photochemical transitions: a feature which is due to perpendicular transition dipoles of the B isomer of these chromophores. Photo-orientation reveals the symmetry nature of photoisomerization transitions. We also report on the observation of near-pure photo-orientation by photoisomerization of azo dye in polymers; an observation which is attributed to both the particular molecular structure of the polymer studied and to appropriate photoisomerization quantum yields as well as as fast trans implied by cis thermal isomerization, and is rationalized by the study of photo-orientation of a series of azo-polyurethanes each with distinct differences in the molecular structure of the unit building blocks.
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Zouheir Sekkat, Hidekazu Ishitobi, Daisuke Yasumatsu, Satoshi Kawata, "Photo-orientation movement of photoisomerizable chromophores: quantifying analytical theory and application to spectrally overlapping and distinguishable isomers", Proc. SPIE 4106, Linear, Nonlinear, and Power-Limiting Organics, (29 November 2000); doi: 10.1117/12.408499; https://doi.org/10.1117/12.408499
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