脂环构象异构化在含有四取代环己烷的偶氮苯官能化交联聚酰亚胺光机械性能中的作用,ACS Macro Letters

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脂环构象异构化在含有四取代环己烷的偶氮苯官能化交联聚酰亚胺光机械性能中的作用
ACS Macro Letters ( IF 5.1 ) Pub Date : 2021-01-26 , DOI: 10.1021/acsmacrolett.0c00903
David H Wang ₁ , Kyung Min Lee ₁ , Deborah H Lee ₁ , Matthew Baczkowski ₁ , Hajin Park ₁ , Michael E McConney ₁ , Loon-Seng Tan ₁

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环己烷的经典“椅子-扭转船-船”构象动力学 (CD) 是热激活的。在这里，我们报告了基于 1,2,4,5-环己烷-四羧酸-二酐的双边稠合环己烷部分的光诱导/偶氮苯辅助 CD，有助于交联偶氮苯官能化聚酰亚胺 (X-azoPI) 的大光机械响应（CHDA），表现出光弯曲角和光生应力，分别高达~90°和370 kPa。相比之下，含有平面均苯四甲酰亚胺 (PMDI) 或笼状双环[2.2.2]oct-7-ene-2,3,5,6-四羧酸二亚胺 (BCDI) 的 X-azoPI 显示出较小的光机械响应。X-azoPI 具有受限的环己烷二亚胺 (CHDI) 单元的优异光机械性能归因于包含“铰链”对苯环、偶氮苯、和交叉链接站点中的 CHDI 单元。蓝光照射引发由连接到 CHDI 单元的偶氮苯的光异构化/重新定向驱动的运动，然后放大其 CD，导致更远范围的分段迁移率、更多的局部自由体积，并最终导致大的光致弯曲。重新分布的 CHDI 立体异构体在 X-azoPI 骨架中的捕获T_房间与观察到的光热记忆有关。

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Role of Alicyclic Conformation-Isomerization in the Photomechanical Performance of Azobenzene-Functionalized Cross-Linked Polyimides Containing Tetra-Substituted Cyclohexane Moieties

The classical “chair-twist boat–boat” conformational dynamics (CD) of cyclohexane is thermally activated. Here we report on the photoinduced/azobenzene-assisted CD of bilaterally fused cyclohexane moieties contributing to large photomechanical response of cross-linked azobenzene-functionalized polyimides (X-azoPI), based on 1,2,4,5-cyclohexane-tetracarboxylic-dianhydride (CHDA), exhibiting a photobending angle and photogenerated stress, up to ∼90° and 370 kPa, respectively. In contrast, X-azoPI containing planar pyromellitimide (PMDI) or cage-like bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic-diimide (BCDI) show smaller photomechanical responses. The superior photomechanical performance of X-azoPI with constrained cyclohexane-diimide (CHDI) units is attributed to an increased mobility of segments comprising “hinged” p-phenylene rings, azobenzene, and CHDI units in the cross-link sites. Blue light irradiation initiates the motions driven by photoisomerization/reorientation of azobenzenes connected to CHDI units, whose CD is then amplified, leading to longer-range segmental mobility, more local free volume, and culminating in large photoinduced bending. The trapping of redistributed CHDI’s stereoisomers in X-azoPI backbone at T_room is implicated for the observed photothermal memory.

更新日期：2021-02-16

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