One F atom matters: synthesis, aggregation-induced emission and stimuli-responsiveness of three isomers of fluoro/formyl substituted tetraphenylethene derivatives

By introducing fluorine atom(s) into luminescent organic compounds, it may be possible to fine-tune their packing structure and luminescence properties. In the present work, three isomers of fluoro/formyl substituted tetraphenylethene (TPE) derivatives ( 1-3 ) with one fluorine atom have been synthesized via the Suzuki-Miyaura cross-coupling reactions in high yields. With the different substitution positions of fluoro/formyl substituents, compounds 1-3 exhibit different luminescence behavior in THF/H 2 O mixed solvents and solid state, as well as responsiveness towards mechanical force and heat when compared with the non-fluorinated analogs TPE-4CHO , TPE-3CHO and TPE-2CHO . Compounds 1 and 3 exhibit mechanofluorochromism with red-shifted emissions, more drastic than those of TPE-4CHO and TPE-2CHO , while 2 and TPE-3CHO do not show this property under the same conditions. Compounds 1-3 all show thermofluorochromism with weaker and blue-shifted emissions on increasing temperatures, different from those of the non-fluorinated analogs, which only exhibit weaker emissions without a wavelength shift under the same conditions. Furthermore, the three compounds form composites with silica gel or filter paper strips, and the resulting composites show stronger and red-shifted emissions compared to the corresponding compounds, and also exhibit thermofluorochromism, which has potential in fluorescent thermometers and anti-counterfeiting. The luminescence properties of three fluorinated tetraphenylethene (TPE) derivatives indicate that the fluorine atom has a significant effect on the solid state packing, and thus the emissions and the stimuli-responsiveness.