Unravelling the Consequences of Aromatic Core-Substitution on Redox-Active Molecular Triangles

Electron delocalisation in shape-persistent molecular triangles occurs as a result of cyclic aromatic homoconjugation between the aromatic diimide (ADI) faces, where π-orbital overlap occurs despite being separated by non-conjugating chiral (R,R)- or (S, S)-trans-1,2-diaminocyclohexane linkers and provides the macrocycles with attractive supramolecular and optoelectronic properties. Despite core-functionalised ADIs being well-explored in the literature, core-substitution of the pyromellitic diimide (PMDI) based molecular triangle was not studied until 2023. This Thesis further explores the effect of core-substitution on the structural, dynamic and optoelectronic properties of molecular triangles comprised of functionalised PMDI faces.

In Chapter 2, the presence of bromine atoms in the only previously reported core-functionalised PMDI based molecular triangle is utilised to synthesise a hexa-arylated macrocycle via a Suzuki–Miyaura cross-coupling reaction. The structural and optoelectronic properties of the resulting core-functionalised molecular triangles are studied to investigate the influence of core-substitution with six electron-withdrawing or -donating groups. In Chapter 3, the dynamic structural properties of analogous tris-brominated and tris-arylated molecular triangles are studied as well as the role of the cyclic aromatic homoconjugated π-surface in the cavity of the macrocycles in facilitating intra- and intermolecular non-covalent interactions. In Chapter 4, the solution and solid-state emission of brominated PMDI phosphors when incorporated into a rigid macrocycle is studied whilst progress towards the synthesis of emissive core-hydroxylated macrocycles using photochemical and conventional methods is presented. Lastly, Chapter 5 presents initial experiments to study the structural and optoelectronic properties of the five molecular triangles synthesised in Chapters 2 and 4 in thin films to assess their potential for application as organic semiconductors in ion-gated transistors and photovoltaic devices. This Thesis highlights the beneficial supramolecular and optoelectronic properties that can be accessed through the functionalisation of PMDI based molecular triangles to inspire further expansion of the scope of the class of macrocycles in the future.