Fast dynamics in the optical storage with Langmuir-Blodgett films of a diazocrown ether molecule
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Azobenzene-containing molecules have been studied for a number of applications exploiting the efficient trans-cis-trans photoisomerization cycles, which lead to molecular alignment and even micrometer-scale mass transport. One of the limitations of these materials, though, is the slow dynamics of the alignment process that requires significant molecular rearrangement. In this paper, we report on Langmuir-Blodgett (LB) films of a derivative of azocrown ether, referred to as 29-membered diazocrown ether, specially synthesized for the photoisomerization to involve only distortion of the shape of the crown. As a result, the dynamics of the writing process was extremely fast, with maximum birefringence being reached within less than 1 s, to be contrasted with tens or even hundreds of seconds for other azobenzene materials. A disadvantage is this strategy, however, is that the resulting birefringence was low, of the order of 10(-3), because the closely packed arrangement prevented the whole diazocrown molecule to be fully reoriented. From a comparison with results obtained in guest-host, cast films where the 29-membered cliazocrown ether was incorporated into a polystyrene matrix, we confirmed that both fast dynamics and small birefringence features are due to a combination of effects from the nanostructured nature of the LB films and the molecular structure of the specially-designed diazocrown ether. Significantly, the fast dynamics opens the way for various applications, as in command surfaces for liquid crystal devices.