Figure 2.

(A) Normalized absorption (dashed) and emission (solid) data of KR-1 and KR-3 in CH₂Cl₂. (B) Normalized absorption (dashed) and emission (solid) data of KR-1 in PBS pH 7.4. (C) Normalized absorption (dashed) and emission (solid) data of KR-3 in PBS pH 7.4. (D) Normalized absorption (dashed) and emission (solid) data of KR-2 in CH₂Cl₂ (black trace) and CH₂Cl₂ supplemented with 5% TFA (red trace). (E) Exo-KR-4 (250 μM) in PBS buffered from pH 7.5 (black trace) to pH 3.5 (red trace) to generate KR-4. (F) Plot of absorbance intensity at ${\lambda }_{\mathrm{m}\mathrm{a}\mathrm{x}}=875\mathrm{n}\mathrm{m}$ vs pH; sigmoidal plot fit resulted in apparent ${\mathrm{p}\mathrm{K}}_{\mathrm{a}}=4.4$.