Time-resolved spectroscopy of the singlet excited state of betanin in aqueous and alcoholic solutionsElectronic supplementary information (ESI) available: Ultrafast transient spectra and kinetics, TD-DFT calculations, and experimental details. See DOI: 10.1039/c5cp00684h

• Main Authors: Wendel, Monika, Nizinski, Stanislaw, Tuwalska, Dorota, Starzak, Karolina, Szot, Dominika, Prukala, Dorota, Sikorski, Marek, Wybraniec, Slawomir, Burdzinski, Gotard
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c5cp00684h

The photophysical properties of betanin in aqueous and alcoholic solutions were determined at room temperature using ultrafast UV-vis-NIR transient absorption spectroscopy ( λ exc = 535 nm). Its S 1 → S n ( n > 1) absorption bands appear with maxima at about λ ∼ 450 and 1220 nm. The short betanin S 1 state lifetime (6.4 ps in water) is mainly determined by the efficient S 1 → S 0 radiationless relaxation, probably requiring a strong change in geometry, since the S 1 lifetime grows to 27 ps in the more viscous ethylene glycol. The fluorescence quantum yield is very low ( Φ f ∼ 0.0007 in water), therefore this deactivation path is of minor importance. Other processes, such as S 1 → T 1 intersystem crossing or photoproduct formation, are virtually absent, since full S 0 ← S 1 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 . Transient UV-vis-NIR absorption of betanin in water.