Visible light-triggered photochemical reactions in aqueous media are highly valuable to tailor molecular structures and properties in an ecofriendly manner. Here we report visible light-induced catalyst-free [2 + 2] cycloadditions of thermoresponsive dendronized styryltriazines, which show tunable microconfinement to guest dyes in aqueous media. These dendronized styryltriazines are constituted of conjugated mono- or tristyryltriazines, which carry hydrophilic dendritic oligoethylene glycol (OEG) pendants. They underwent efficient [2 + 2] cycloadditions to form dendronized cyclobutane dimers or oligomers in water through irradiation with visible light of 400 nm, and their cycloaddition behavior was dominated by dendritic architectures and solvent conditions. Dendronization with dendritic OEGs also afforded them characteristic thermoresponsive properties with tunable phase transition temperatures in the range 36–65 °C, which can be further modulated through photocycloaddition of styryltriazine chromophores. Importantly, dendronized styryltriazines can form tunable microenvironments in aqueous media, which encapsulate hydrophobic solvatochromic Nile red to exhibit variable photophysical properties. The encapsulated guest dye can be simultaneously released through noninvasive visible light-induced [2 + 2] cycloaddition reactions.

中文翻译：

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热响应树枝状苯乙烯三嗪的可见光[2 + 2]环加成表现出可调节的微限制


水介质中可见光触发的光化学反应对于以生态友好的方式定制分子结构和性能非常有价值。在这里，我们报道了可见光诱导的热响应树枝化苯乙烯基三嗪的无催化剂[2 + 2]环加成，其在水性介质中表现出对客体染料的可调微限制。这些树枝状苯乙烯基三嗪由共轭单苯乙烯基三嗪或三苯乙烯基三嗪组成，其带有亲水性树枝状低聚乙二醇（OEG）侧链。通过400 nm可见光的照射，它们在水中进行有效的[2 + 2]环加成反应，形成树枝状环丁烷二聚体或低聚物，并且它们的环加成行为由树枝状结构和溶剂条件主导。树枝状 OEG 的树枝化还赋予它们特有的热响应特性，相变温度在 36-65 °C 范围内可调，可以通过苯乙烯三嗪发色团的光环加成进一步调节。重要的是，树枝状苯乙烯三嗪可以在水介质中形成可调节的微环境，其封装疏水性溶剂化变色尼罗红以表现出可变的光物理性质。封装的客体染料可以通过非侵入性可见光诱导的[2 + 2]环加成反应同时释放。