State Key Laboratory of Supramolecular Structure and Materials, Jilin University, No. 2699 Qianjin Street, Changchun, P. R. China.
Phys Chem Chem Phys. 2018 Dec 12;20(48):30297-30303. doi: 10.1039/c8cp06363j.
A series of two-component co-crystals driven by IN interactions based on the bipyridine (BIPY) chromophore with one among three different co-former building blocks, iodopentafluorobenzene (IPFB), 1,4-diiodotetrafluorobenzene (DITFB) and 1,3,5-trifluoro-2,4,6-triiodobenzene (IFB), were prepared and analysed via infared spectroscopy and single-crystal X-ray diffraction. By comparing the IN distances in the co-crystal structures, we found that the higher the -F ratio in the building blocks the closer the contact of the IN bond, enhancing the intermolecular interactions in these co-crystals as well. That is, the positive electrostatic potential on the iodine atom(s) in the co-formers was enhanced by the presence of strong electron-withdrawing groups. The distinct spectroscopic behaviours (fluorescence and Raman spectra) among the two-component BIPY co-crystal systems in response to hydrostatic pressure were also investigated. Interestingly, the fluorescence of BIPY-DITFB presented intriguing abnormal evolution from dark to bright, suggesting a new charge transfer state due to the decreased intermolecular distance and the enhanced IN interactions. Theoretical simulations by Materials Studio also showed the shortened IN distance and the increased angle of C-IN, evidencing the enhanced IN interactions. In contrast, BIPY-IFB showed only slightly enhanced fluorescence intensity at 550 nm consistent with BIPY-DITFB. Once the pressure was relieved, both the Raman and fluorescence spectra for BIPY co-crystal systems entirely self-recovered. Remarkable emission enhancement in a solid-state co-crystal has been rarely reported in previous publications and in fact, this study paves a unique way for designing and developing novel stimuli-responsive photo-functional materials.
基于联吡啶（BIPY）发色团，与三种不同共晶构筑块之一碘五氟苯（IPFB）、1,4-二碘四氟苯（DITFB）和 1,3,5-三氟-2,4,6-三碘苯（IFB），制备了一系列由 IN 相互作用驱动的双组分共晶，并通过红外光谱和单晶 X 射线衍射进行了分析。通过比较共晶结构中的 IN 距离，我们发现共晶构筑块中的-F 比例越高，IN 键的接触越近，从而增强了这些共晶中的分子间相互作用。也就是说，共晶构筑块中碘原子上的正静电势能因强吸电子基团的存在而增强。我们还研究了两种组分 BIPY 共晶体系对静水压力的不同光谱响应（荧光和拉曼光谱）。有趣的是，BIPY-DITFB 的荧光从暗到亮呈现出有趣的异常演变，表明由于分子间距离减小和 IN 相互作用增强，出现了新的电荷转移态。Materials Studio 的理论模拟也表明 IN 距离缩短和 C-IN 角度增加，证明了 IN 相互作用的增强。相比之下，BIPY-IFB 在 550nm 处仅表现出略微增强的荧光强度，与 BIPY-DITFB 一致。一旦压力得到缓解，BIPY 共晶体系的拉曼和荧光光谱完全自行恢复。在以前的出版物中很少有关于固态共晶中显著发射增强的报道，事实上，这项研究为设计和开发新型刺激响应光功能材料开辟了一条独特的途径。
