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首页> 外文期刊>Chemistry: A European journal >Phase-dependent photochromism of a lactone-stabilized chromene from a flavylium reaction network
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Phase-dependent photochromism of a lactone-stabilized chromene from a flavylium reaction network

机译：黄酮反应网络中内酯稳定的色烯的相变光致变色

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New trans-2-hydroxychalcones bearing a carboxylate group at position 2′ (Ct-) were synthesized (compounds 2 and 3). These compounds lead to a network of chemical reactions depending on pH value, light, and solvent. In water, when the pH value is lowered, the ionized trans-chalcone is protonated and the flavylium cation AH+ is formed at very acidic pH values through hemiketal B and cis-chalcone Cc, with global acidity constants of pK′a ≤-1 and ≈0.1, respectively, for 2 and 3. The electron-acceptor character of the carboxylic substituent not only increases the observed acidity of the flavylium cation, but also decreases the rate of the ring-opening/-closing from a subsecond timescale to hours relative to model compound 1 (without carboxylate). The photochemistry of the network was studied in detail by means of continuous irradiation, monitored by UV/Vis absorption and ~1H and ~(13)NMR spectroscopic analysis. Although compound 3 is only slightly photoactive, compound 2 (Ct;bsupesup) reacts in aqueous solutions (λirr=313 nm) to form B-and Cc -, with a global quantum yield of 0.15, and fully reverts back to Ct- with a rate constant of k=6.7× 10~(-5) s ~(-1). The flavylium cation is no longer formed in methanol, and irradiation of Ct- leads to the formation of B- and the new lactone-trapped chromene species La. The formation of La takes place through a sequence of three photochemical steps: photoisomerization of Ct-, photo-ring-closing reaction of Cc-, and photolactonization of B -. Only the cis/trans isomerization and ring-closing reactions are thermally reversible on a timescale of seconds and hours, respectively. A photochromic system was achieved in rigid matrices of methanol (at 77 K) and 1-dodecanol (5 °C) by irradiating lactone La to give a red ortho-quinone allide through a photo-ring-opening reaction; the color disappears with a rate constant of k=1.25× 10~(-2) s~(-1) in 1-dodecanol at 5 °C.
机译：合成了新的在位置2'（Ct-）带有羧基的反式-2-羟基查耳酮（化合物2和3）。这些化合物会导致化学反应网络，具体取决于pH值，光线和溶剂。在水中，当pH值降低时，离子化的反查尔酮质子化，并且在半酸性状态下，通过半缩醛B和顺式查尔酮Cc形成黄酮阳离子AH +，全局酸度常数为pK'a≤-1和分别对于2和3≈≈0.1。羧酸取代基的电子受体特性不仅增加了所观察到的黄酮阳离子的酸度，而且还将开环/闭合的速率从亚秒级降至相对于小时数小时。建模化合物1（不含羧酸盐）。通过连续照射，通过UV / Vis吸收以及〜1H和〜（13）NMR光谱分析对网络的光化学进行了详细研究。尽管化合物3仅具有轻微的光活性，但化合物2（Ct; bupesup）在水溶液（λirr= 313 nm）中反应形成B-和Cc-，整体量子产率为0.15，并完全还原为Ct-。速率常数k = 6.7×10〜（-5）s〜（-1）。黄酮阳离子不再在甲醇中形成，而Ct-的辐射导致形成B-和新的内酯捕获的色烯物种La。La的形成通过三个光化学步骤进行：Ct-的光异构化，Cc-的光环闭合反应和B-的光内酯化。仅顺式/反式异构化和闭环反应分别在几秒和几小时的时间尺度上是可热逆的。通过内酯La的辐照，通过光环开环反应生成红色的邻醌内酯，从而在甲醇（77 K）和1-十二烷醇（5°C）的刚性基质中获得光致变色体系。颜色在5°C下于1-十二烷醇中以k = 1.25×10〜（-2）s〜（-1）的速率常数消失。

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