Start Date
2018
Description
Scopoletin is suspected to undergo excited-state proton transfer (ESPT), resulting in fluorescent emission from the anionic structure except in very low pH. Excitation and emission spectra were collected in water of varying pH and were used to determine the pKₐ of ground-state and excited-state scopoletin to be 7.6 ± 0.2 and 1.7 ± 0.2 respectively. This agrees with literature’s calculated value for the ground state [3] and the literature excited-state value for a molecule of similar structure [6]. Spectra were then collected using tetrahydrofuran as a solvent to force neutral conditions and added sodium metal to force anionic conditions. These spectra provide further evidence for ESPT occurring in protic solvents as both neutral and anionic fluorescent spectra were found to be distinct in aprotic tetrahydrofuran.
Recommended Citation
Pham, Hunter T. and Muyskens, Mark, "Scopoletin Excited-State Proton Transfer and Excited-State pKₐ" (2018). Summer Research. 1.
https://digitalcommons.calvin.edu/summer_research/2018/Posters/1
Scopoletin Excited-State Proton Transfer and Excited-State pKₐ
Scopoletin is suspected to undergo excited-state proton transfer (ESPT), resulting in fluorescent emission from the anionic structure except in very low pH. Excitation and emission spectra were collected in water of varying pH and were used to determine the pKₐ of ground-state and excited-state scopoletin to be 7.6 ± 0.2 and 1.7 ± 0.2 respectively. This agrees with literature’s calculated value for the ground state [3] and the literature excited-state value for a molecule of similar structure [6]. Spectra were then collected using tetrahydrofuran as a solvent to force neutral conditions and added sodium metal to force anionic conditions. These spectra provide further evidence for ESPT occurring in protic solvents as both neutral and anionic fluorescent spectra were found to be distinct in aprotic tetrahydrofuran.