Insight into the strong aggregation-induced emission of low-conjugated racemic C6-unsubstituted tetrahydropyrimidines through crystal-structure-property relationship of polymorphs.
Insight into the strong aggregation-induced emission of low-conjugated racemic C6-unsubstituted tetrahydropyrimidines through crystal-structure-property relationship of polymorphs.
复制标题
通过多晶型物的晶体-结构-性质关系洞察低共轭外消旋C6-未取代四氢嘧啶的强聚集诱导发射
DOI：
10.1039/c5sc01226k
复制
发表时间：
2015-08-01
期刊：
影响因子：
8.4
通讯作者：
Tang BZ
中科院分区：
文献类型：
--
作者：
Zhu Q;Zhang Y;Nie H;Zhao Z;Liu S;Wong KS;Tang BZ
外消旋低共轭非发射THPS 1-3可以形成高发射的RS-和RR/SS-堆积多晶型，并具有混合的通键和穿透空间共轭。外消旋C6-未取代四氢嘧啶类化合物(THPS)是一类具有强聚集诱导发射(AIE)效应的荧光团。然而，它们不具备传统AIE化合物的结构特征。为了了解它们的AIE机理，本文用三种THPS(1-3)的7种晶型研究了分子堆积方式和构象对THPS光学性质的影响。外消旋THPS 1-3具有低共轭和高度柔性的分子结构，因此在不同的有机溶剂中几乎没有发射。然而，它们的多晶型的荧光量子产率高达93%，最大激发波长(λex)和发射波长(λem)分别长达40 9 nm和4 84 nm。单晶结构和基于λex和λem值的理论计算表明，具有最短的λex和λem值的多晶型具有RS堆积模式(R-和S对映体以成对反平行线的形式自组装)和较扭曲的构象，而二元酸之间没有通过空间共轭；而具有较长的λex和λem值的多晶型采用RR/SS-堆积模式(R-和S对映体以不成对的之字线自组装)和较少的扭曲构象。所有这些多晶型中的1-3的分子构象都是立体的，比溶液中的分子构象更扭曲。虽然1-3的共轭能力较差，但其多晶型的辐射速率常数(Kr)与传统的荧光团一样大(0.41-1.03×108 S-1)，这是因为通过键和空间相互作用改善了电子共轭。根据所得到的结果，可以推断，强AIE不仅源于分子内运动的限制，还源于增强的电子耦合以及辐射有利的交叉局域激发(LE)和分子内电荷转移(ICT)激发态。反常的分子结构、易于控制的R-和S对映体的自组装以及较强的AIE效应使得THPS具有非常有用的荧光分子应用和理论研究。
Racemic low-conjugated non-emissive THPs 1–3 can form highly emissive RS- and RR/SS-packing polymorphs with mixed through-bond and through-space conjugation. Racemic C6-unsubstituted tetrahydropyrimidines (THPs) are a series of fluorophores with a strong aggregation-induced emission (AIE) effect. However, they do not possess the structural features of conventional AIE compounds. In order to understand their AIE mechanism, here, the influences of the molecular packing mode and the conformation on the optical properties of THPs were investigated using seven crystalline polymorphs of three THPs (1–3). The racemic THPs 1–3 have low-conjugated and highly flexible molecular structures, and hence show practically no emission in different organic solvents. However, the fluorescence quantum yields of their polymorphs are up to 93%, and the maximum excitation (λ ex) and emission (λ em) wavelengths of the polymorphs are long at 409 and 484 nm, respectively. Single-crystal structures and theoretical calculation of the HOMOs and LUMOs based on the molecular conformations of these polymorphs indicate that the polymorphs with the shortest λ ex and λ em values possess a RS-packing mode (R- and S-enantiomers self-assemble as paired anti-parallel lines) and a more twisted conformation without through-space conjugation between the dicarboxylates, but the polymorphs with longer λ ex and λ em values adopt a RR/SS-packing mode (R- and S-enantiomers self-assemble as unpaired zigzag lines) and a less twisted conformation with through-space conjugation between the dicarboxylates. The molecular conformations of 1–3 in all these polymorphs are stereo and more twisted than those in solution. Although 1–3 are poorly conjugated, the radiative rate constants (k r) of their polymorphs are as large as conventional fluorophores (0.41–1.03 × 108 s–1) because of improved electronic conjugation by both through-bond and through-space interactions. Based on the obtained results, it can be deduced that the strong AIE arises not only from the restriction of intramolecular motion but also from enhanced electronic coupling and radiatively-favored inter-crossed local excitation (LE) and intramolecular charge transfer (ICT) excitation states. The abnormal molecular structures, easily-controllable self-assembly of the R- and S-enantiomers, and the strong AIE effect make THPs very useful fluorophores for applications and theoretical research.
登录
查看更多内容
影响因子：
8.4
作者：
Choi, Sohee;Bouffard, Jean;Kim, Youngmi
通讯作者：
Kim, Youngmi
影响因子：
4.3
作者：
Gong, Zhong-Liang;Zhong, Yu-Wu;Yao, Jiannian
通讯作者：
Yao, Jiannian
影响因子：
4.3
作者：
Hu, Rongrong;Lam, Jacky W. Y.;Tang, Ben Zhong
通讯作者：
Tang, Ben Zhong
影响因子：
4.9
作者：
Huang, Jing;Sun, Ning;Li, Zhen
通讯作者：
Li, Zhen
影响因子：
8.6
作者：
Chen, JW;Law, CCW;Tang, BZ
通讯作者：
Tang, BZ