Browsing by Author "Ras, Robin H. A., Prof., Aalto University, Department of Applied Physics, Finland"

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  • Light-fuelled motions in azobenzene-containing materials: From supramolecular design to new applications
    (2014) Koskela, Jenni E.
     School of Science | Doctoral dissertation (article-based)
    Azobenzene-containing materials represent a versatile class of stimuli-responsive systems, in which light can be used to trigger a variety of fascinating phenomena. Owing to their rapid and reversible photoisomerization, azobenzenes are efficient molecular photoswitches that enable effective control over a number of properties of the host material. Moreover, the nanoscale photoisomerization reaction can actuate various large-scale molecular motions in the system, such as the light-driven macroscopic mass transport. Under certain conditions, polarized light can be used to induce macroscopic movement in a glassy material, which results in a well-defined topographic pattern on the film surface. During the past two decades, a vast amount of research has been devoted to understand the microscopic origin of these motions. On the other hand, the light-induced phenomena in azomaterials have demonstrated huge potential in numerous application areas ranging from photonics to biology. Still, many aspects of the intricate relationship between the light-triggered macroscopic effects and the material properties remain unresolved.  This thesis aims to unveil new possibilities for the light-induced motions in terms of material design and application potential. Importantly, the recent advancements in supramolecular design of light-responsive materials are exploited in order to present new implications on the surface patterning phenomenon and to explore its fundamental limits. First, hydrogen-bonded azobenzene–polymer complexes with versatile optical properties over a broad spectral range are presented. Secondly, azobenzene-oligomer complexes with extremely low azobenzene content are used to systematically seek for the lowest amount of azobenzene that is still capable of inducing mass transport. The phenomenon is also taken to another extreme, as the light-induced surface patterns are shown to occur in azobenzene-functionalized dendrimers and native biomolecules with exceptionally high molecular weight. Finally, the immense yet largely unexploited application potential of the light-induced surface patterning is discussed and the use of the patterns in the nanofabrication of plasmonic hole arrays is demonstrated. This thesis presents new means to understand the complex structure-performance relationships in azomaterials and suggests novel uses for the light-induced surface patterns.
  • Photoluminescent Gold Nanoclusters in Soft Matrices
    (2023) Zhou, Shaochen
     School of Science | Doctoral dissertation (article-based)
    Photoluminescent gold nanoclusters (AuNCs), composed of several to tens of gold atoms, are versatile ultrasmall nanomaterials that show promise in applications like imaging, sensing, lighting, and catalysis. However, the inferior photoluminescence performance and lack of functional properties, have hindered AuNCs from extensive application. This thesis discusses AuNCs confined in three types of soft matrices, namely assemblies, double-layered structures, and polymers. Confinement of AuNCs in the soft matrices can result in great performance improvement and interesting functional properties. The mechanisms behind the performance enhancement and functional properties are studied and discussed. The AuNCs in the soft matrices show potential for various applications. Publication 1 establishes supraparticles as a promising soft matrix for AuNCs, achieving a significant improvement in photoluminescence emission brightness and resistance to photobleaching. Publication 2 reports a dual-layered oxide shell as an effective matrix for AuNCs, achieving comprehensive enhancement in stability. Publication 3 introduces a simple, direct strategy for both generation and encapsulation of AuNCs in the polymer film, exhibiting moderate photoluminescence efficiency and excellent shelf and photo-stability. Publication 4 outlines that confinement of AuNCs in the aliphatic tertiary amine group-rich polymer scaffold leads to pH-responsive near-infrared emission, promising great bio-application potential. Overall, these works demonstrate various strategies for obtaining gold nanoclusters with improved photoluminescence performance and functional properties.