Santagata, Emanuela (2026) New crystalline materials for telecommunications and advanced functional applications. [Tesi di dottorato]

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Abstract

Crystal Engineering has emerged as a crucial tool for investigating how intermolecular interactions dictate crystal packing, enabling the rational design of molecular crystal architectures with predetermined structures and functions. The design pathway, therefore, begins with the target application, extends to the selection of suitable synthons, and culminates in the choice of molecular functional groups. Within this framework, this PhD project employs crystal engineering principles across two distinct research lines, both relying on the idea that controlling intermolecular interactions enables the design and understanding of advanced organic crystalline materials. The first research line focuses on the development of new ionic and neutral acentric organic crystals for nonlinear optical (NLO) applications, with particular targeting on terahertz (THz) radiation generation. The primary goal was the design and synthesis of compounds crystallising in polar, acentric space groups, an essential requirement for NLO applications. To address this, a library of push–pull chromophores incorporating new electron-acceptor units paired with diverse donors and counterions was synthesised. Moreover, a newly developed class of neutral imines showed a particularly strong propensity to form polar, acentric structures, promoted through hydration or by the use of targeted weak interactions, including hydrogen and halogen bonding. The second research line, instead, investigates polymorphism, solid–solid phase transitions, and mechanically responsive materials. The work was carried out in collaboration with several research groups. Specifically, Nonlinear Optics microscopy and Hyper-Rayleigh Scattering (HRS) were performed in collaboration with Professor Koen Clays and Dr. Yovan de Coene at the KU Leuven; Second-Harmonic Generation (SHG) measurements were conducted with Prof. Stefano Lettieri at the University of Naples Federico II; preliminary THz generation tests with Dr. Mojca Jazbinsek at the Zurich University of Applied Sciences, and Raman spectroscopy with Prof. Elena Simone and Dr. Emmanuele Parisi at the Politecnico di Torino. Furthermore, the synthesis of the mesogenic polyphenyl compounds was conducted in partnership with Professor Przemysław Kula at the Military University of Technology of Warsaw, while the computational analysis related to Raman spectra was performed in collaboration with Professor Timothy M. Korter at Syracuse University (New York).

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