Fig. 4. Halochromism of P_SP1, P_SP2, P_SP3, P_SP4 in DCM from UV-vis spectroscopy. (A–D) TFA addition (1.0 eq.), (E–H) MsOH addition (1.0 eq.). Time until equilibration is indicated. Molar concentration of SP moiety: 100–150 μM. (I–N) Comparison of the kinetics among four polymers upon acid addition. Normalized absorbance was used in (M and N) to enable a qualitative comparison of the response rate of the polymers toward TFA and MsOH acid. The A_MCH⁺/A_SP ratio is used instead of A_MCH⁺ to factor in the concentration difference between experiments assuming A_MCH⁺/A_SP ∼ c_MCH⁺/c_SP with ε_MCH⁺/ε_SP = constant. A_MCH⁺ refers to the absorbance (A) of the MCH⁺ form at λ_max in the visible range, and A_SP refers to the absorbance of the pristine SP at λ_max.