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

K. Ouhenia-Ouadahi, R. Metivier, S. Maisonneuve, A. Jacquart, J. Xie, A. Leaustic, P. Yu and K. Nakatani Photochemical & Photobiological Sciences, 2012, 11, 11, 1705-14

A thorough photophysical study of a photochrome-fluorophore dyad (3), combining a fluorescent laser dye (DCM-type, , Phi(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 (Phi(-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 Phi(EET)(OF-->F) = 85% and as Phi(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 tau(-OF) = 70 ps and 170 ps essentially to tau(-OF) < 10 ps) and to the values of Forster radii determined for 3 (R(0)(OF --> F) = 29 A and R(0)(F --> CF) = 71 A), evidencing a Forster-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 (alpha(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.

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Publication

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Paru le 6 juillet 2012

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doi10.1039/c2pp25129a