Browsing by Author "Priimägi, Arri, Dr., Aalto University, Finland"

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    Design of efficient photoresponsive azobenzene materials through supramolecular functionalization
    (Aalto University, 2013) Vapaavuori, Jaana; Priimägi, Arri, Dr., Aalto University, Finland; Teknillisen fysiikan laitos; Department of Applied Physics; Group of Optics and Photonics; Perustieteiden korkeakoulu; School of Science; Kaivola, Matti, Prof., Aalto University, Finland
    Azobenzene molecules are known to change their geometry upon photon absorption. The photoisomerization process, taking place at the nanometer scale, can give rise to remarkable photoinduced macroscopic motions into the material system. The most pronounced examples of such effects are photoinduced bending of free-standing films and the formation of micron-scale surface patterns due to photoinduced mass transport. Due to their anisotropic shape, azobenzenes also contain directional information and are polarization sensitive. The phenomena arising from the photoisomerization reaction have applications not only in optics and photonics, but also in the interfaces between light and surface science, information storage, imaging, biology, energy storage and actuation. Despite the extensive research, many fundamental questions concerning the coupling between the molecular-scale reactions and the photoresponse of the material at larger scales still remain a conundrum. This thesis seeks for guidelines for designing efficient photoresponsive materials through exploiting the toolkit of supramolecular chemistry. Supramolecular functionalization  provides a powerful tool for precisely controlling the composition of the material system, which is imperative when exploring the structure–performance relationships that govern the material's light-responsive behavior. By  selecting the constituent compounds in a systematic and controlled manner, we study the effect of the structural and physical parameters of the azobenzene units on their packing density, which again profoundly influences their optical performance. More specifically, the role of  (i) chromophore-chromophore intermolecular interactions, (ii) flexible spacer groups, (iii) the polarity of the azobenzene units, and (iv) the architecture of the host material on photoalignment and photoinduced surface patterning are discussed. In addition to contributing to fundamental understanding of light-matter interactions in azobenzene-containing materials, our findings highlight more generally the potential of supramolecular material design in optics and photonics, and we believe that this interface will bring about applications far beyond the scope now seen.