Properties of Parent and F-Labeled pH Indicators
| Parent compound | Monofluorinated | Difluorinated | ||||
| Indicator name | pKa | λmax | pKa | λmax | pKa | λmax |
| Phenol red | 7.9 | 558 | 7.3 | 564 | 6.4 | 570 |
| Cresol red | 8.2 | 572 | 7.6 | 576 | 6.8 | 582 |
| Cresol purple | 8.3 | 578 | 7.5 | 582 | 7.0 | 590 |
| Phenolphthalein | 9.7 | 553 | 9.3 | 558 | 8.7 | 564 |
| Naptholphthalein | 7.8 | 653 | 7.7 | 659 | 7.2 | 665 |
pKa = negative logarithm of acid dissociation constant (unitless); λmax = absorbance maximum of basic form in nm.