title: Time-resolved spectroscopy of the singlet excited state of betanin in aqueous and alcoholic solutions.
abstract: The photophysical properties of betanin in aqueous and alcoholic solutions were determined at room temperature using ultrafast UV-vis-NIR transient absorption spectroscopy (λexc = 535 nm). Its S1 → Sn (n > 1) absorption bands appear with maxima at about λ ∼ 450 and 1220 nm. The short betanin S1 state lifetime (6.4 ps in water) is mainly determined by the efficient S1 → S0 radiationless relaxation, probably requiring a strong change in geometry, since the S1 lifetime grows to 27 ps in the more viscous ethylene glycol. The fluorescence quantum yield is very low (Φf ∼ 0.0007 in water), therefore this deactivation path is of minor importance. Other processes, such as S1 → T1 intersystem crossing or photoproduct formation, are virtually absent, since full S0 ← S1 ground state recovery is observed within tens of picoseconds after photoexcitation. The observed fast light-to-heat conversion in the absence of triplet excited state formation supports the idea that betanin is a photoprotector in vivo.
authors.affiliation: Quantum Electronics Laboratory, Faculty of Physics, Adam Mickiewicz University in Poznan, Umultowska 85, 61-614 Poznan, Poland. gotardb@amu.edu.pl.
authors.forename: Monika
authors.initials: M
authors.lastname: Wendel
authors.forename: Stanislaw
authors.initials: S
authors.lastname: Nizinski
authors.forename: Dorota
authors.initials: D
authors.lastname: Tuwalska
authors.forename: Karolina
authors.initials: K
authors.lastname: Starzak
authors.forename: Dominika
authors.initials: D
authors.lastname: Szot
authors.forename: Dorota
authors.initials: D
authors.lastname: Prukala
authors.forename: Marek
authors.initials: M
authors.lastname: Sikorski
authors.forename: Slawomir
authors.initials: S
authors.lastname: Wybraniec
authors.forename: Gotard
authors.initials: G
authors.lastname: Burdzinski
mesh_terms: D050859:Betacyanins / Q000737:chemistry*; D019855:Ethylene Glycol / Q000737:chemistry; D000432:Methanol / Q000737:chemistry*; D011789:Quantum Theory; D012996:Solutions / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D014867:Water / Q000737:chemistry*
chemical_list: D050859:Betacyanins; D012996:Solutions; D014867:Water; C020228:betanin; D019855:Ethylene Glycol; D000432:Methanol