Organic chromophores find widespread use in diverse applications, significantly advancing our understanding of natural phenomena. Contemporary research allows us to engineer organic chromophores with desired characteristics, encompassing redox attributes, optical properties, solubility, and more. Nonetheless, transitioning from design to synthesis and comprehending the inherent structural properties can pose challenges, necessitating the creation of novel molecules with unique properties for in-depth study.

Early-stage functionalization is commonly thought of as a bad strategy since making a library of molecules will require much more synthetic work compared to late-stage functionalization. Notably, early-stage functionalization involving NCS on the triangulenium precursor (acridinium) has emerged as a valuable strategy, enabling milder, previously inaccessible sitespecific functionalization. In the process, a highly selective intramolecular substitution was found, sparking further investigation into the mechanism and resulting in the proof of the proposed mechanism for the synthesis of DMQA. The target compounds showed that by chlorination, we could tune the redox properties of ADOTA and DAOTA.

While ADOTA and DAOTA exhibit similar optical properties, their oxidation and reduction potentials differ significantly. The variation in oxidation potential was a main factor in a comprehensive investigation of three different PET groups. This study explored the relationship between the rate of PET and chromophore redox properties, as well as the design principles of the PET group. It was found that introducing a twist in the linker from the quencher to triangulenium reduced the rate of PET by a factor of 20. In all cases the extend of the fluorescence quenching was high, with least quenched having a relative fluorescence quantum yield in the OFF-state of below 3 %. Meaning that more than 97 % of the emission was quenched.

Finally, new hetero dyads consisting of PDI and a triangulenium chromophore were studied. The first focused on making the HOMO and LUMO energies of the chromophores degenerate. The degenerate energy levels resulted in the discovery of a unique reversible PET state. The reversibility was due to the degeneracy of the HOMO energies. By conducting transient absorption experiments, we were able to explain the excited state processes in the dyad, which gave rise to the multiexponential fluorescence lifetimes. When increasing solvent polarity, the non-radiative decay increased, resulting in a relative fluorescence quantum yield of 9 % in a 1:1 mixture of ACN and DCM. Furthermore, we could make the LUMO degenerate when switching to highly polar DMF, which was observed by measuring absorption in the reduced dyad. In DMF, we observed the radical being located partially on both chromophores. The second dyad solely focused on making the energy of the S0  S1 transition equal to learn more about the excited state. The investigation revealed that the exciton was jumping between the two chromophores, resulting in the properties being a weighted average of PDI and DAOTA. This equilibrium could be tuned by the solvent; hence, in DCM, we found approximately 40% PDI emission, and when going to toluene, we observed only about 10 % PDI emission.

This newly gained insight into the relationship between structure and properties holds promise for the development of organic chromophores with enhanced redox and optical characteristics.