Photo-induced dynamics in a pyrene–isoalloxazine(flavin)–phenothiazine triad

• Published in: Chemical physics Vol. 337; no. 1; pp. 99 - 109
• Main Authors: Shirdel, J., Penzkofer, A., Shen, Z., Procházka, R., Daub, J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 16-08-2007
• Subjects: Absorption spectroscopy; Blue-light photoreceptor model; Charge recombination; Cryptochrome model; Flavin; Fluorescence spectroscopy; Förster-type energy transfer; Isoalloxazine; Oxidative electron transfer; Phenothiazine; Photo-degradation; Pyrene; Reductive electron-transfer; Triad; Absorption spectroscopy; Fluorescence spectroscopy; Förster-type energy transfer; Reductive electron-transfer; Charge recombination; Isoalloxazine; Blue-light photoreceptor model; Pyrene; Flavin; Oxidative electron transfer; Cryptochrome model; Triad; Photo-degradation; Phenothiazine
• ISSN: 0301-0104
• DOI: 10.1016/j.chemphys.2007.06.044

(α
R)-α-[[[10-[4-(10-heptyl-10
H-phenothiazin-3-yl)phenyl]-4,10-dihydro-2,4-dioxobenzo[
g]pteridin-3(2
H)-yl]acetyl]amino]pyrenepropionic acid phenylmethyl ester, a pyrene–isoalloxazine(flavin)–phenothiazine triad (abbreviated as PYFPT), was designed to mimic the dye-based functions of cryptochromes. PYFPT dissolved in dichloromethane and acetonitrile is characterized by absorption and fluorescence spectroscopy. Absorption cross-section spectra, fluorescence quantum distributions and quantum yields, degrees of fluorescence polarisation, and fluorescence lifetimes are determined. The triad is highly photo-stable as has been shown by monitoring absorption spectra under prolonged blue-light exposure. The absorption spectrum of PYFPT resembles the superposition of the absorption of the isoalloxazine (flavin), pyrene, and phenothiazine subchromophores. Blue light (
λ
exc
=
428
nm) excites exclusively the isoalloxazine subunit causing reductive electron transfer from the phenothiazine subchromophore to the locally excited isoalloxazine with a time constant of approximately 600
fs under formation of a charge transfer state which subsequently undergoes charge recombination. Near ultraviolet radiation (
λ
exc
=
311
nm) causes simultaneous excitation of the isoalloxazine, pyrene, and phenothiazine chromophores. Both, the locally excited pyrene and phenothiazine moieties cause oxidative electron transfer to the flavin moiety with time constants of about 80
ps and 50
ps followed by subsequent charge recombination. Förster-type energy transfer processes have been found to be one to two orders of magnitude slower.