PPSM, ENS Cachan, CNRS, UMR8531, 61 av. Président Wilson, F-94235 Cachan cedex, France.
Photochem Photobiol Sci. 2012 Nov;11(11):1705-14. doi: 10.1039/c2pp25129a.
A thorough photophysical study of a photochrome-fluorophore dyad (3), combining a fluorescent laser dye (DCM-type, , 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(-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(-OF) = 70 ps and 170 ps essentially to τ(-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.
本文对通过点击化学合成的光致变色-荧光染料二聚体（3）进行了全面的光物理研究，该二聚体结合了一种荧光激光染料（DCM 型， ，Φ(1) = 0.27）和一种光致变色二芳基乙烯（2）。除光致变色外，2 的开环形式（OF）还具有荧光（Φ(-OF) = 0.016），而闭环形式（CF）则没有。通过交替的 UV/可见光照射 2 可以切换荧光。2-OF 的发射带与 1 的吸收带（400-550nm）匹配，而 1 的发射带与 2-CF 的吸收带（550-700nm）重叠。因此，在二聚体 3 中获得了由光致变色部分状态控制的光致可逆双向能量转移（EET）。通过比较 1、2 和 3 的发射和激发光谱，定量确定它们的效率为 Φ(EET)(OF→F) = 85%和 Φ(EET)(F→CF)~100%。这些结果与荧光寿命的缩短（从 τ(-OF) = 70 ps 和 170 ps 基本缩短到 τ(-OF) < 10 ps）以及为 3 确定的Förster 半径值完全兼容（R(0)(OF → F) = 29 Å 和 R(0)(F → CF) = 71 Å），证明了Förster 型共振能量转移机制（FRET）。这种双向 FRET 的一个重要结果是，在 UV 照射下，3 在 PSS 中可以猝灭 49%的荧光，这对应于光致变色反应的转化程度，与 2 不同（α(CF) = 91%）。这是一个明显的例子，表明光致变色单元和荧光团之间的 FRET 存在会显著影响二聚体分子 3 的光致变色性质。
