Recent developments in super-resolution microscopy have significantly expanded the requirements for switchable dyes, leading to demand for specially designed molecular switches. We report the synthesis and characterization of a spironaphthoxazine photochromic switch (a derivative of palatinate purple) displaying high photoconversion (85–95%) under readily accessible 405 nm light, broad absorption in the visible, and excellent fatigue resistance. The indole substituent on this spironaphthoxazine is twisted out of conjugation with the naphthalene unit, yet it is crucial for activation with visible light. The open colored merocyanine form of the spironaphthoxazine reverts to the closed form with a lifetime of 4.7 s in dichloromethane at 20 °C; this thermal reversion is even faster in more polar solvents. The photochemical quantum yields for ring-opening and ring-closing are approximately 8% and 1%, respectively, in dichloromethane. The ring-opening and ring-closing reactions have been characterized by time-resolved infrared and transient absorption spectroscopies. Ring opening occurs rapidly (τ = 2.1 ns) and efficiently (∼90%) from the singlet excited state to form an intermediate (assigned as a cisoid merocyanine), which returns to the closed ground state (τ = 4.5 ns) in competition with relaxation to the transoid open form (τ = 40 ns). Photochemical ring closing is a faster and simpler process: the excited state proceeds to the closed spirooxazine with a time constant of 0.28 ns. This photochromic switch can be used in conjunction with commercial fluorescent dyes to create a small-molecule switchable fluorescent dyad that shows high contrast and good fatigue resistance in living cells. These properties make the dyads suitable for application in RESOLFT microscopy.

中文翻译：

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用于生物成像的螺萘恶嗪可切换染料†

超分辨率显微镜的最新发展显着扩大了对可切换染料的要求，导致对特殊设计的分子开关的需求。我们报告了螺萘恶嗪光致变色开关（巴拉丁紫的衍生物）的合成和表征，该开关在容易接近的 405 nm 光下显示出高光转换率（85-95%）、在可见光中的广泛吸收和出色的抗疲劳性。这种螺萘恶嗪上的吲哚取代基与萘单元的共轭扭曲，但它对于可见光的活化至关重要。螺萘恶嗪的开放有色部花青形式在 20 °C 下在二氯甲烷中恢复为封闭形式，寿命为 4.7 秒；在极性更大的溶剂中，这种热回复甚至更快。在二氯甲烷中，开环和闭环的光化学量子产率分别约为 8% 和 1%。开环和闭环反应已通过时间分辨红外和瞬态吸收光谱进行了表征。开环迅速发生（τ = 2.1 ns）和有效（~90%）从单重激发态形成中间体（指定为顺式部花青），它返回到闭合基态（τ = 4.5 ns）与松弛到 transoid 开放的竞争形式（τ = 40 ns）。光化学闭环是一个更快、更简单的过程：激发态以 0.28 ns 的时间常数进入闭合的螺恶嗪。这种光致变色开关可与商业荧光染料结合使用，形成一种小分子可切换荧光双联体，在活细胞中显示出高对比度和良好的抗疲劳性。这些特性使二元组适用于 RESOLFT 显微镜。