Proceeding to the excited states of Cz-BDT and Cz-AQ, we first endeavour to find a computational method that describes their states accurately. To do so, we consider experimental results as well as reference calculations at the ab initio ri-ADC(2)/TZVP level of theory. Experimental results are presented in Table . Cz-BDT is found to have an absorption maximum at 2.65 eV and a strongly red-shifted emission at 1.87 eV. In the case of Cz-AQ both values are about 0.3 eV higher. Table also highlights the considerable difference of the fluorescence quantum yield Φ measured in solution between the two molecules, showing a more than sixfold drop when going from Cz-AQ to Cz-BDT. Whereas, the shift in absorption and emission maxima can be explained by the lowering of the LUMO, it is harder to gain understanding of the drop in quantum yield.