Metal‐Free Facile Synthesis of Multisubstituted 1‐Aminoisoquinoline Derivatives with Dual‐State Emissions
Xinyu Zhang, Yibin Zhou, Mengzhu Wang, Yating Chen, Yunbing Zhou, Wenxia Gao, Miaochang Liu, Xiaobo Huang, Huayue Wu
Abstract
Although isoquinoline is a good traditional fluorescent structural unit, most of its derivatives emit fluorescence in solution and a few of them can emit solid-state fluorescence as well. Herein, a series of multisubstituted 1-aminoisoquinoline derivatives were synthesized by a simple reaction of a readily available 4H-pyran derivative and secondary amines. The reaction had advantages of metal-free, mild conditions, simple operation, and good yields, which was realized by a ring-opening and sequential ring-closing mechanism. These 1-aminoisoquinoline derivatives were found to exhibit interesting dual-state emissions. In the solution, they emitted strong blue fluorescence at about 458 nm. In the solid state, they emitted solid-state blue fluorescence at 444-468 nm with high fluorescence quantum yields of 40.3-98.1%. Crystal structural analyses indicated that solid-state emissions of these compounds originated from twisted molecular conformations and the resultant loose stacking arrangements. Furthermore, their solid-state fluorescence wavelengths were demonstrated to depend on molecular conformations rather than stacking arrangements. The discovery of these 1-aminoisoquinolines with multiple reaction sites provides new possibilities for the development of solid-state fluorescent materials based on the traditional isoquinoline skeleton.