Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Chemistry. 2012 Apr 10;18(15):4634-43. doi: 10.1002/chem.201103518. Epub 2012 Feb 29.
The construction and precise control of the face-to-face π-stacked arrangements of anthracene fluorophores in the crystalline state led to a remarkable red shift in the fluorescence spectrum due to unprecedented excited oligomer formation. The arrangements were regulated by using organic salts including anthracene-1,5-disulfonic acid (1,5-ADS) and a variety of aliphatic amines. Because of the smaller number of hydrogen atoms at the edge positions and the steric effect of the sulfonate groups, 1,5-ADS should prefer face-to-face π-stacked arrangements over the usual edge-to-face herringbone arrangement. Indeed, as the alkyl substituents were lengthened, the organic salts altered their anthracene arrangement to give two-dimensional (2D) edge-to-face and end-to-face herringbone arrangements, one-dimensional (1D) face-to-face zigzag and slipped stacking arrangements, a lateral 1D face-to-face arrangement like part of a brick wall, and a discrete monomer arrangement. The monomer arrangement behaved as a dilute solution even in the close-packed solid state to emit deep blue light. The 1D face-to-face zigzag and slipped stacking of the anthracene fluorophores caused a red shift of 30-40 nm in the fluorescence emission with respect to the discrete arrangement, probably owing to ground-state associations. On the other hand, the 2D end-to-face stacking induced a larger red shift of 60 nm, which is attributed to the excimer fluorescence. Surprisingly, the brick-like lateral face-to-face arrangement afforded a remarkable red shift of 150 nm to give yellow fluorescence. This anomalous red shift is probably due to excited oligomer formation in such a lateral 1D arrangement according to the long fluorescence lifetime and little shift in the excitation spectrum. The regulation of the π-stacked arrangement of anthracene fluorophores enabled the wide modulation of the fluorescence and a detailed investigation of the relationships between the photophysical properties and the arrangements.
在晶体状态下构建并精确控制蒽荧光团面对面的π堆积排列，由于前所未有的激发寡聚物形成，导致荧光光谱发生显著红移。这些排列通过使用包括蒽-1,5-二磺酸（1,5-ADS）和各种脂肪胺在内的有机盐进行调节。由于边缘位置的氢原子数量较少，以及磺酸盐基团的空间位阻效应，1,5-ADS 应该优先采用面对面的π堆积排列，而不是通常的边缘面对面的鱼骨排列。事实上，随着烷基取代基的延长，有机盐改变了它们的蒽排列，形成二维（2D）边缘面对面和端到端鱼骨排列、一维（1D）面对面之字形和滑移堆积排列、类似于部分砖墙的横向 1D 面对面排列以及离散的单体排列。即使在紧密堆积的固态中，单体排列也表现为稀溶液，发射深蓝色光。蒽荧光团的 1D 面对面之字形和滑移堆积导致荧光发射相对于离散排列红移 30-40nm，可能归因于基态缔合。另一方面，2D 端到端堆积导致荧光发射红移 60nm，这归因于激基荧光。令人惊讶的是，砖状的横向面对面排列提供了显著的 150nm 红移，产生黄色荧光。这种异常的红移可能归因于这种横向 1D 排列中激发寡聚物的形成，根据长荧光寿命和激发光谱的小位移。蒽荧光团的π堆积排列的调节实现了荧光的广泛调制，并对光物理性质与排列之间的关系进行了详细研究。
