title: Acid effect on photobase properties of curcumin.
abstract: Femtosecond UV-vis pump-probe spectroscopy was employed to study the acid effect on curcumin in the excited state. Curcumin in solutions of weak acids was found to be a photobase forming a protonated curcumin within a few tens of picoseconds from the time of excitation. The excited-state protonation reaction is also observed in the steady-state emission spectrum as a new red emission band with a maximum at 620 nm in the presence of weak acids. The transient pump-probe spectrum consists of four spectral bands, two emission bands, and two absorption bands. We assign a transient absorption band at ∼600 nm and an emission band at ∼540 nm to the neutral ROH form of curcumin. An absorption band at ∼500 nm and an emission band at 620 nm are assigned to the protonated ROH2(+) form of curcumin.
authors.affiliation: Department of Physics of Complex Systems, Weizmann Institute of Science , Rehovot 76100, Israel.
authors.forename: Katherine
authors.initials: K
authors.lastname: Akulov
authors.forename: Ron
authors.initials: R
authors.lastname: Simkovitch
authors.forename: Yuval
authors.initials: Y
authors.lastname: Erez
authors.forename: Rinat
authors.initials: R
authors.lastname: Gepshtein
authors.forename: Tal
authors.initials: T
authors.lastname: Schwartz
authors.forename: Dan
authors.initials: D
authors.lastname: Huppert
mesh_terms: D000143:Acids / Q000737:chemistry*; D003474:Curcumin / Q000737:chemistry*; D015394:Molecular Structure; D011522:Protons; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors
chemical_list: D000143:Acids; D011522:Protons; D003474:Curcumin