We propose that the comparatively high efficacy of SBPs in photocatalytic hydrogen evolution stems from their electronic make-up -in particular, from their ability to effectively separate photoexcited charge carriers. To determine the lifetime of the excited states, we performed timecorrelated single-photon counting (TCSPC) experiments. The lifetimes obtained from triexponential decay fitting are similar to those of previously reported triarylborane-based donoracceptor systems and other solid donor-acceptor hydrogen evolution catalysts. The weighted average lifetime τavg is longest for BDT-TAB (0.259 ns), followed by TT-TAB (0.180 ns) and BT-TAB (0.104 ns). From the absolute lifetimes, we surmise that the first (τ1) and second (τ2) decay processes are too fast and that the excitons are too short lived to contribute significantly to the (diffusion-limited) photocatalytic process. Interestingly, however, the longest lifetime τ3 has a similar weight in all materials (of between 4 and 7 %), and it decreases going from TT-TAB (2.960 ns) via BDT-TAB (2.000 ns) to BT-TAB (0.920 ns). This lifetime decrease follows the same trend as the observed catalytic activities (with TT-TAB as highest, and BT-TAB as lowest) (Figure and Table ).