The employed acceptor unit BDT is an electron deficient ringfused heterocycle and a synthetic intermediate towards the synthesis of the fully aromatic and strongly-electron donating benzodithiophene moiety which is widely exploited in high performance donor polymers for organic solar cells. While benzodithiophene has seen great utilisation as a donor, BDT itself has received much less attention as an acceptor unit despite its deep LUMO energy which is ca. 0.39 V lower than that of the carbocyclic homologue anthraquinone. Cz-BDT was designed to complement one of the best reported red TADF luminogens at the time, Cz-AQ, and induce a redshift in emission due to the lower LUMO of BDT. This did lead to a >100 nm redshift in emission wavelength compared to Cz-AQ, and TADF was evident from the characteristic double decay in the transient absorbance spectra, however the photoluminescence quantum yield (PLQY) was greatly reduced in both solution and dilute thin film measurements from ≈0.60 for Cz-AQ in solution to <0.10 for Cz-BDT. We note that in the meantime alternative strategies in the design of red TADF emitters have led to high PLQY extending into the near infrared range. Nonetheless, identifying the root cause of the vast drop in PLQY between Cz-AQ and Cz-BDT presents a useful challenge to inform future molecular design and to provide deep insight into the photophysics of TADF emitters along with methodological challenges in its computational description.