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首页> 外文期刊>Chemistry: A European journal >o-Nitrobenzyl photolabile protecting groups with red-shifted absorption: Syntheses and uncaging cross-sections for one- and two-photon excitation
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o-Nitrobenzyl photolabile protecting groups with red-shifted absorption: Syntheses and uncaging cross-sections for one- and two-photon excitation

机译：具有红移吸收的邻硝基苄基光不稳定保护基：用于单光子激发和双光子激发的合成和解笼截面

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摘要

We evaluated the o-nitrobenzyl platform for designing photolabile protecting groups with red-shifted absorption that could be photolyzed upon one- and two-photon excitation. Several synthetic pathways to build different conjugated o-nitrobenzyl backbones, as well as to vary the benzylic position, are reported. Relative to the reference 4,5-dimethoxy-2-nitrobenzyl group, several o-nitrobenzyl derivatives exhibit a large and red-shifted one-photon absorption within the near-UV range. Uncaging after one-photon excitation was studied by measuring UV-visible absorption and steady-state fluorescence emission on model caged ethers and esters. In the whole series investigated, the caged substrates were released cleanly upon photolysis. Quantum yields of uncaging after one-photon absorption lie within the 0.1-1 % range. We observed that these drop as the maximum wavelength absorption of the o-nitrobenzyl protecting group is increased. A new method based on fluorescence correlation spectroscopy (FCS) after two-photon excitation was used to measure the action uncaging cross section for two-photon excitation. The series of o-nitrobenzyl caged fluorescent coumarins investigated exhibit values within the 0.1-0.01 Goeppert-Mayer (GM) range. Such results are in line with the low quantum yields of uncaging associated with cross-sections of 1-50 GM for two-photon absorption. Although the cross-sections for one- and two-photon absorption of o-nitrobenzyl photolabile protecting groups can be readily improved, we emphasize the difficulty in enlarging the corresponding action uncaging cross-sections in view of the observed trend of their quantum yield of uncaging.
机译：我们评估了邻硝基苄基平台，以设计具有红移吸收的光不稳定保护基，该保护基可在单光子和双光子激发后被光解。报道了建立不同的共轭邻硝基苄基骨架以及改变苄基位置的几种合成途径。相对于参考4,5-二甲氧基-2-硝基苄基，几种邻硝基苄基衍生物在近紫外范围内表现出大的红移单光子吸收。通过测量模型笼状醚和酯的紫外可见吸收和稳态荧光发射，研究了单光子激发后的解笼。在整个研究过程中，笼罩的底物在光解后被干净地释放。一光子吸收后的解开量子产率在0.1-1％范围内。我们观察到，随着邻硝基苄基保护基团最大波长吸收的增加，这些下降。一种基于荧光相关光谱法（FCS）的双光子激发后的新方法用于测量双光子激发的作用解开截面。研究的邻硝基苄基笼状荧光香豆素系列显示的值在0.1-0.01 Goeppert-Mayer（GM）范围内。这样的结果与用于双光子吸收的与1-50 GM的横截面相关的解开的低量子产率相符。尽管邻硝基苄基光不稳定保护基的单光子和双光子吸收截面易于改善，但鉴于观察到的解开量子产率的趋势，我们强调了扩大相应作用解开截面的困难。 。

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