Chen Yi, Chen Deng-Gao, Chen Yi-An, Wu Cheng-Ham, Chang Kai-Hsin, Meng Fan-Yi, Chen Meng-Chi, Lin Jia-An, Huang Chun-Ying, Su Jianhua, Tian He, Chou Pi-Tai
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology Shanghai, 200237, Shanghai, P. R. China.
Department of Chemistry, National Taiwan University, Taipei, 10617, R.O.C., Taiwan.
Chemistry. 2019 Dec 20;25(72):16755-16764. doi: 10.1002/chem.201904900. Epub 2019 Dec 6.
With the aim of generalizing the structure-properties relationship of bending heterocyclic molecules that undergo prominent photoinduced structural planarization (PISP), a series of new dihydrodibenzo[ac]phenazine derivatives in which one nitrogen atom is replaced by oxygen (PNO), sulfur (PNS), selenium (PNSe), or dimethylmethanediyl (PNC) was strategically designed and synthesized. Compounds PNO, PNS, and PNSe have significantly nonplanar geometries in the ground state, which undergo PISP to give a planarlike conformer and hence a large emission Stokes shift. A combination of femtosecond early relaxation dynamics and computational approaches established an R*→I* (intermediate)→P* sequential kinetic pattern for PNS and PNSe, whereas PNO undergoes R*→P* one-step kinetics. The polarization ability of the substituted heteroatoms, which is in the order O<S<Se, correlates with their increase in π conjugation, and hence the Stokes shift of the emission is in the order PNO<PNS<PNSe. Compound PNSe with the largest PISP barrier was shown to be a highly sensitive viscosity probe. Further evidence for heteroatom-harnessing PISP is given by PNC, in which the dimethylmethanediyl substituent lacks lone pair electrons for π extension, showing the normal emission of the bent structure. The results led to the conclusion that PISP is ubiquitous in dihydrodibenzo[ac]phenazines, for which the driving force is elongation of the π delocalization to gain stabilization in the excited state.
为了概括经历显著光致结构平面化（PISP）的弯曲杂环分子的结构-性质关系，我们有策略地设计并合成了一系列新的二氢二苯并[ac]吩嗪衍生物，其中一个氮原子被氧（PNO）、硫（PNS）、硒（PNSe）或二甲基亚甲基（PNC）取代。化合物PNO、PNS和PNSe在基态具有显著的非平面几何结构，它们经历PISP形成类似平面的构象异构体，从而产生较大的发射斯托克斯位移。飞秒早期弛豫动力学和计算方法相结合，为PNS和PNSe建立了R*→I*（中间体）→P的顺序动力学模式，而PNO经历R→P*的一步动力学。取代杂原子的极化能力顺序为O<S<Se，这与其π共轭的增加相关，因此发射的斯托克斯位移顺序为PNO<PNS<PNSe。具有最大PISP势垒的化合物PNSe被证明是一种高度灵敏的粘度探针。PNC给出了杂原子利用PISP的进一步证据，其中二甲基亚甲基取代基缺乏用于π扩展的孤对电子，显示出弯曲结构的正常发射。结果得出结论，PISP在二氢二苯并[ac]吩嗪中普遍存在，其驱动力是π离域的延长以在激发态获得稳定性。
