Clemens-Schöpf-Institute, Technical University of Darmstadt (TUDa), Alarich-Weiss-Straße 4, DE 64287 Darmstadt, Germany.
Institute for Condensed Matter Physics, Technical University of Darmstadt (TUDa), Hochschulstraße 8, DE 64289 Darmstadt, Germany.
J Am Chem Soc. 2023 Feb 15;145(6):3615-3623. doi: 10.1021/jacs.2c12760. Epub 2023 Feb 7.
Two polyaspartates bearing -fluorinated azobenzenes (FAB) as photo-responsive groups in the side chain were synthesized: PFABLA () and co-polyaspartate PpFABLA--PBLA [, 75%(n/n) PFABLA content]. As a consequence of the /-isomerization of the side chain, PFABLA () undergoes a visible-light-induced reversible coil-helix transition in solution: Green light (525 nm) affords the coil, and violet light (400 nm) affords the helix. FAB significantly increases the thermal stability of the -isomer at 20 °C ( = 66 d for the -isomer) and effectively counters the favored back formation of the helix. At 20%(w/w) polymer concentration, the helical polymer forms a lyotropic liquid crystal (LLC) that further orients unidirectionally inside a magnetic field, while the coil polymer results in an isotropic solution. The high viscosity of the polymer solution stabilizes the coexistence of liquid crystalline and isotropic domains, which were obtained with spatial control by partial light irradiation. When used as an alignment medium, PFABLA () enables (i) the measurement of dipolar couplings without the need for a separate isotropic reference and (ii) the differentiation of enantiomers. PpFABLA--PBLA () preserves the helical structure, by intention, independently of the /-isomerization of the side chain: Both photo-isomers of PpFABLA--PBLA () form a helix that─at a concentration of 16%(w/w)─form an LLC. Despite the absence of a change in the secondary structure, the /-isomerization of the side chain changes the morphology of the liquid crystal and leads to different sets of dipolar coupling for the same probe molecule.
两个带有 - 氟代偶氮苯（FAB）作为侧链光响应基团的聚天冬氨酸被合成：PFABLA（）和共聚物聚天冬氨酸 PpFABLA-PBLA [，75%（n/n）PFABLA 含量]。由于侧链的 /-异构化，PFABLA（）在溶液中经历可见光诱导的可逆卷曲-螺旋转变：绿光（525nm）提供卷曲，紫光（400nm）提供螺旋。FAB 显著提高了 - 异构体在 20°C 时的热稳定性（= 66d 为 - 异构体），并有效地阻止了螺旋的有利回形成。在 20%（w/w）聚合物浓度下，螺旋聚合物形成溶致液晶（LLC），在磁场内进一步单向取向，而卷曲聚合物则导致各向同性溶液。聚合物溶液的高粘度稳定了液晶和各向同性区域的共存，这些区域通过部分光照射获得空间控制。当用作取向介质时，PFABLA（）能够（i）测量偶极耦合，而无需单独的各向同性参考，以及（ii）区分对映异构体。PpFABLA-PBLA（）有意地保留了螺旋结构，独立于侧链的 /-异构化：PpFABLA-PBLA（）的两种光异构体都形成螺旋，在 16%（w/w）浓度下形成 LLC。尽管二级结构没有变化，但侧链的 /-异构化改变了液晶的形态，并导致相同探针分子的偶极耦合有不同的集合。
