A Tale of Chaos and Colour Influencing the photophysical properties and glass forming abilities of BODIPY dyes via structural modification

Abstract

Organic dyes are everyday contributors in chemistry, physics and biology. BODIPY dyes were used as model dye class in this thesis. They are well-known for their versatility, which mainly originates from the tuneability of their photophysical properties upon changes in their molecular structure. This thesis strives to deepen the knowledge of the structure-to-photophysical properties relationship of those fluorophores. Furthermore, it demonstrates how the intrinsic properties of the dye can be influenced by modifying the molecular structure. Structural homologues of the BODIPY and the aza-BODIPY class were synthesised. The homologues differ only in the bridging atom. Moreover, they are decorated with electron withdrawing and donating groups. The effects of those groups were analysed for each class individually and additionally compared within the two classes. This revealed different behaviours of the two dye classes that were previously unexplored. To strategically decrease the singlet-triplet energy gap, a BODIPY-anthracene dyad, which populates a charge separated state, and can then undergo charge recombination into the triplet state, was oligomerised. Oligomerisation in a non-conjugated fashion mimics a fixed J-aggregate thus facilitating strong exciton coupling. This lowers the singlet state of the oligomers, without having a large effect on the triplet energy. Therefore, the energy gap, which can be described as the energy loss of the system, can be decreased. Furthermore, a new dye material, a room temperature dye glass, was fabricated. BODIPY derivatives equipped with different alkyl chains were synthesised and subsequently mixed. Upon mixing the entropy of the system is increased, leading to a decrease in the materials ability to crystallise and aggregate. The material now forms an amorphous solid state, a glass, which inherits the monomeric optical properties of the dye components. The results presented in this thesis highlight that by modifying the molecular structure of a dye molecule, its intrinsic properties can be governed according to ones needs. This is of great importance for the in vivo design of dyes as well as the fabrication of new materials.