Synthesis, Properties and Application of New Chiral Squaraine Dyes for Optoelectronic Devices

Abstract

The work presented in this thesis investigates a broad range of squaraine dyes, systematically varying their molecular design and terminal n-alkyl substituents in order to optimize aggregation behavior and the associated (chir)optical properties. Following their successful synthesis, each squaraine is systematically investigated for their aggregation behaviour in both solution and thin films, with a focus on chiral characteristics where applicable. The results providing important insights into how molecular structure governs supramolecular organisation and, in turn, the observed (chiro)optical properties.<br /> A central question addressed consistently in this work is the underlying arrangement of chromophores and the mechanism responsible for the remarkably strong chiroptical responses observed in these systems. By exploring the added value of chirality, the resulting circular dichroism (CD) response is used to probe these arrangements. This allows their original nature to be identified: bisignate signals were assigned to strongly coupled Coulombic Frenkel excitons, whereas monosignate peaks were linked to intermolecular charge transfer (ICT) interactions. Using this principle on several occasions in combination with other analytical methods, allowed the unimpeachable identification of ICT interactions as a recurring and fundamental element in the aggregation behavior of squaraines.<br /> Together, these results establish a coherent framework for understanding structure-property relationships in squaraines, while demonstrating the practical potential of these materials through their application in an organic photodetector.