Fig. 3. Excited state dynamics of TCPP in the intermediate concentration range. (a) Transient absorption (TA) heatmap for TCPP (excitation into Q_y(1,0) at 515 nm) in an acidic environment (128 mM MSA). The photoinduced absorption (red area) around 1 ms is absent in the measurements presented before. (b) Spectral slices of the heatmap at delay times 0.6 μs, 3.0 μs, 9.1 μs, 24 μs, 63 μs, 160 μs, 0.4 ms, 1.0 ms, 2.5 ms, and 6.4 ms from blue to red. The photoinduced absorption is visible in the orange spectra and located at 22.4 × 10³ cm⁻¹ (446 nm). (c) The TA spectrum at 1.0 ms, same as in panel b, overlapped with in black the difference between the steady-state UV/vis spectrum of 4 mM and 1024 mM presented in Fig. 1(c) scaled arbitrarily. The good overlap between the two proves that the final state in the TA measurements is a photoinduced protonated ground state. (d) Altered Jablonski diagram for TCPP in acidic environment but not fully protonated (region II). (e) Proposed excited-state relaxation and (de)protonation dynamics used for the global fit analysis in panel e, f (see ESI,† S2 for rate equations). (f) Time trace slices of the heatmap at energies 23.9, 22.4, and 19.0 × 10³ cm⁻¹, like indicated in the heatmap in panel a, with the global fit results (lines). (g) The three spectra of the three states in the global fit model. The three corresponding rates are 11.3, 8.0, and 0.69 ms⁻¹. They compare well with separately collected spectra (see Fig. S6, ESI†). (h) The protonation (k_p,T in red) and deprotonation (k_dp,HS in blue) rates obtained by global fitting the transient absorption data on the MSA concentrations 32, 64, 128, and 256 mM. The grey line shows the H₂TCPP²⁺ concentration obtained from steady-state UV/vis also shown in Fig. 1(c) and is scaled arbitrarily.