Effects of Halogenation on Quinoline-Malononitrile-based AIEgens: Photophysical Properties Investigation and Wash-Free Imaging.

Developing halogen-functionalized fluorescent dyes with intriguing photophysical properties, including enhanced photostability, is particularly important for bioimaging. In this work, we synthesized two new halogen-functionalized aggregation-induced emission (AIE)-active molecules, DQMF-OH and DQMCl-OH, based on the quinoline-malononitrile chromophore. The halogen effect on the photophysical characteristics was detailedly studied by absorption and fluorescence spectroscopy, density functional theory calculations, and crystal structures. Compared with non-halogen substituted AIE luminogen (AIEgen) DQM-OH, the halogen substituted DQMF-OH and DQMCl-OH exhibited red-shifted absorptions and emissions in the solution and solid state. In addition, DQMF-OH and DQMCl-OH also possessed enhanced fluorescence toward viscosity changes. These AIEgens served as remarkable imaging tools for cell tracking in a wash-free manner. Furthermore, DQMF-OH and DQMCl-OH showed much more excellent photobleaching resistance than DQM-OH. Our work sheds new light on developing fluorescent halogenated dyes with enhanced photophysical performances for biological applications.