Fluorescence photoswitching and photoreversible two-way energy transfer in a photochrome—fluorophore dyad

• Published in: Photochemical & photobiological sciences 2012-11, Vol.11 (11), p.1705-1714
• Main Authors: Ouhenia-Ouadahi, Karima, Métivier, Rémi, Maisonneuve, Stéphane, Jacquart, Aurélie, Xie, Juan, Léaustic, Anne, Yu, Pei, Nakatani, Keitaro
• Format: Article
• Language: English
• Subjects: Biochemistry; Biomaterials; Chemical Sciences; Chemistry; Physical Chemistry; Plant Sciences
• ISSN: 1474-905X; 1474-9092
• DOI: 10.1039/c2pp25129a

A thorough photophysical study of a photochrome—fluorophore dyad ( 3 ), combining a fluorescent laser dye (DCM-type, 1 , Φ 1 = 0.27) and a photochromic diarylethene ( 2 ), obtained by click chemistry, is presented. In addition to photochromism, the open form (OF) of 2 exhibits fluorescence ( Φ 2 -OF = 0.016), whereas the closed form (CF) does not. Fluorescence is switched upon alternate UV/visible irradiation of 2 . The emission band of 2 -OF matches the absorption band of 1 (400–550 nm), whereas the emission band of 1 overlaps the absorption band of 2 -CF (550–700 nm). Therefore, a photoreversible two-way excitation energy transfer (EET), controlled by the state of the photochromic moiety, is obtained in the dyad 3 . Their efficiencies are quantified as Φ EET OF→F = 85% and as Φ EET F→CF ~ 100% from the comparison of emission and excitation spectra between 1 , 2 , and 3 . These results are fully compatible with the shortening of fluorescence lifetimes (from τ 2-OF = 70 ps and 170 ps essentially to τ 3-OF < 10 ps) and to the values of Förster radii determined for 3 ( R 0 (OF → F) = 29 Å and R 0 (F → CF) = 71 Å), evidencing a Förster-type resonance energy transfer mechanism (FRET). An important outcome of this two-way FRET is the possibility to quench 49% of the fluorescence in 3 at PSS upon UV irradiation, corresponding to the conversion extent of the photochromic reaction, which is different from 2 ( α CF = 91%). This is a clear example of a situation where the presence of FRET between the photochromic unit and the fluorophore affects noticeably the photochromic properties of the dyad molecule 3 .