Sun Hui, Ye Kaiqi, Wang Chunyu, Qi Haiyan, Li Fei, Wang Yue
Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, Jilin University, Changchun 130012, People's Republic of China.
J Phys Chem A. 2006 Sep 21;110(37):10750-6. doi: 10.1021/jp057232a.
The pi-pi stacked associations of three N,N'-di(n-butyl) quinacridone derivatives, widely used dopants in organic light-emitting diodes, with different sizes of substituents were investigated in solution at various temperatures by (1)H NMR spectroscopy. The pi-pi stacked geometries were estimated by both the magnitudes of peak shifts with concentration and the directions of peak shifts induced by polar solvents. Two patterns of geometries with different pi-pi interaction strengths were found to coexist in solution for all the three samples. In both of the patterns, the preferential orientation of the stacking is the approach of the carbonyl groups on one molecule to the nitrogen atoms on the stacked partner, which makes the pi-deficient aromatic atoms interact with both pi-rich and pi-deficient aromatic atoms of the stacked partner to maximize the electrostatic complementarity. Differently, whereas the molecules in one pattern are face-to-face stacked in a parallel fashion and slip two rings relative to one another along with the long axis of the conjugated ring systems, the molecules in the other are either face-to-face stacked in an antiparallel fashion with slight slipping between layers or stacked in a turning fashion. Both association constants obtained by fitting the dilution curves and thermodynamic parameters obtained from van't Hoff analyses revealed unexpectedly three thermodynamic processes of aggregations for all the three samples in the temperature region of 298-213 K. The size of substituents on the outer aromatic rings significantly influences the pi-pi stacked structures and association thermodynamics.
通过¹H NMR光谱研究了三种N,N'-二（正丁基）喹吖啶酮衍生物（有机发光二极管中广泛使用的掺杂剂）与不同尺寸取代基在不同温度下于溶液中的π-π堆积缔合。通过浓度引起的峰位移大小以及极性溶剂引起的峰位移方向来估算π-π堆积几何结构。发现所有三个样品在溶液中均共存两种具有不同π-π相互作用强度的几何结构模式。在这两种模式中，堆积的优先取向是一个分子上的羰基靠近堆积伙伴上的氮原子，这使得缺π芳香原子与堆积伙伴的富π和缺π芳香原子相互作用，以最大化静电互补性。不同的是，一种模式中的分子以平行方式面对面堆积，并沿着共轭环系统的长轴相对于彼此滑动两个环，而另一种模式中的分子要么以反平行方式面对面堆积且层间有轻微滑动，要么以扭转方式堆积。通过拟合稀释曲线获得的缔合常数以及从范特霍夫分析得到的热力学参数均意外地揭示了所有三个样品在298 - 213 K温度范围内存在三种聚集热力学过程。外芳香环上取代基的大小显著影响π-π堆积结构和缔合热力学。
