Photochemically triggered phase transitions

We have demonstrated that a chiral vesicle composed of di-palmitoyl-L- a-phosphatidylcholine(l-DPPC) doped with the azobenzene containing amphiphiles shown in Scheme 2 is a subject to photochemically triggered phase transition and exhibits a non-linear photoresponse in terms of ICD appearing at the absorption band of azobenzene. 

Image Amplification by Means of Photochemically Triggered Phase Transition in Liquid Crystal... 

A photochemically triggered phase transition is again clearly demonstrated. The apparent increase of the transmittance before its sharp decline is seemingly due to a subtle change in interference of... 

Figure 8. Photochemically triggered phase transition in solid polymer film.

S. Tazuke, S. Kurihara, and T. Ikeda, Amplified image recording in liquid crystal media by means of photochemically triggered phase transition, Chem. Lett. 1987, 911-914. 

Organic compounds which show reversible color change by a photochemical reaction are potentially applicable to optical switching and/or memory materials. Azobenzenes and its derivatives are one of the most suitable candidates of photochemical switching molecular devices because of their well characterized photochromic behavior attributed to trans-cis photoisomerization reaction. Many works on photochromism of azobenzenes in monolayers LB films, and bilayer membranes, have been reported. Photochemical isomerization reaction of the azobenzene chromophore is well known to trigger phase transitions of liquid crystals [29-31]. Recently we have found the isothermal phase transition from the state VI to the state I of the cast film of CgAzoCioN+ Br induced by photoirradiation [32]. 

Photochemical switching of the phase transition is also found in the polyion complex film. Figure 29 shows reversible cycles of the absorption at 370nm by the coupling of the thermal and photoinduced phase transition of the complex film with carboxymethylcellulose 8. In conclusion, we indicate that the immobilized bilayer membranes containing the azobenzene chromophore are available to the erasable memory materials based on the phase transition triggered by thermal and photochemical processes. The polyion complex technique is clearly shown to be a very useful method for materialization of the immobilized bilayer membranes. 

S. Kurihara, T. Ikeda, T. Sasaki, H.-B. Kim, and S. Tazuke, Tune-resolved observation of isothermal phase transition of liquid crystals triggered by photochemical reaction of dopant, J. Chem. Soc., Chem. Commun. 1990, 1751-1752. 

The spectral change due to the UV light irradiation is ascribable to the isothermal phase transition triggered by the photochemical isomerization reaction. The trany-isomer in the metastable solid phase with the head-to-tail chromo-phore orientation is converted to the cfT-isomer by the UV light irradiation. The backward reaction from cis to trans can also partly proceed during the UV light irradiation. When the cast film is irradiated below the solid-to-liquid crystal phase transition temperature, the trans-isomer is regenerated by the backward reaction... 

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