As previously mentioned, 427 nm light selectively excites the HE. To interrogate the mechanism of the reaction, we focused our attention on identifying which species was responsible for the quenching of the excited state of pDTCz-DPmS. As such, the steady-state and time-resolved emission of pDTCz-DPmS in THF were recorded in the presence of each reaction component. It is worth noting that in the case of HE, a lower concentration was used (Table ), otherwise the HE fluorescence band would dominate the emission spectrum (Figure ). In THF, pDTCz-DPmS displays a prompt emission decay with a lifetime, τp, of 4.3 ns and a delayed emission (TADF) decay with lifetime, td, of 3.30 μs in the absence of oxygen. Significant quenching was observed upon addition of each of the reaction components, although this quenching was focused almost exclusively on the delayed emission of pDTCz-DPmS (Table ). The τp remained within 3.5-4.0 ns, reflective of the 4.3 ns lifetime of pDTCz-DPmS in the absence of quencher. Instead, τd was shown to dramatically decrease from 3.30 μs to between 0.046-1.65 μs, depending on the quencher. The quenching rate constants, kq, as estimated from the Stern-Volmer equation, are reported in Table . For all quenchers, kq was very high; on the order of 10 9 -10 10 M -1 s -1 for the prompt emission quenching and 10 8 -10 9 M -1 s -1 for the delayed emission quenching (Table ). The weight of the prompt (Χ PROMPT ) and TADF emission (Χ TADF ) quenching was evaluated by comparison of the corresponding kq for a specific quencher, the lifetimes, and the distribution of the excited state between prompt (Φ PROMPT ) and TADF emission (Φ To rationalize the experimental evidence that the reaction proceeds also in the absence of pDTCz-DPmS, where HE is the predominant species absorbing the excitation light, we studied the quenching of the HE fluorescence in the presence of the other reactants in THF solution.