Anomalous H⁺ and D⁺ Excited-State Proton-Transfer Rate in H₂O/D₂O Mixtures

We used the time-resolved fluorescence technique to measure the excited-state proton-transfer (ESPT) rates from 8-hydroxy-1,3,6-pyrenetrisulfonate (HPTS) to solvent mixtures of H₂O and D₂O. We found an anomalous deviation from linear mole-fraction behavior of the ESPT rate in H₂O/D₂O mixtures. We provide a chemical model based on equilibrium constant of the reaction H₂O + D₂O ↔ 2HOD and rate constants of the ESPT process of H and D transfers from HPTS to the mixed solvent. Anomalous deviation from linear mole-fraction behavior was previously found for H⁺/D⁺ conductance in these mixtures