Diethylamino functionalized tetraphenylethenes: structural and electronic modulation of photophysical properties, implication for the CIE mechanism and application to cell imaging

Deciphering structural and electronic effects on photophysical properties of aggregation-or crystallization-induced emission (AIE or CIE) luminogens is essential to the related mechanistic understanding, molecular design and applications. Herein, based on AIE-active tetraphenylethene (TPE), a group of diethylamino (DEA) functionalized analogues, i.e. DEATPE, DFDEATPE and CNDEATPE were designed and prepared. The introduction of DEA groups makes DEATPE CIE-active rather than typically AIE-active. Further incorporation of fluorine atoms renders DFDEATPE with AIE and crystallization-induced emission enhancement (CIEE) characteristics. Furthermore, unlike the nonmechanochromic TPE, these luminogens exhibit high contrast mechanochromism. Specifically, DEATPE and DFDEATPE demonstrate rapid self-recovery within a few minutes or even several seconds. Such swift restoration of solid emission clearly indicates active intramolecular motions even in the solid states, which is indicative of the CIE mechanism. Additionally, luminogenic nanoparticles were successfully utilized in cell imaging, thanks to their high efficiency and biocompatibility.