Fine Tuning of Emission Behavior, Self-Assembly, Anion Sensing, and Mitochondria Targeting of Pyridinium-Functionalized Tetraphenylethene by Alkyl Chain Engineering

Compared to the many
studies that focus on the development of novel molecular frameworks
pertaining to functionalized fluorescent materials, there is lesser
emphasis on side chains even though they have a significant impact
on the properties and applications of fluorescent materials. In this
study, a series of pyridinium-functionalized tetraphenylethene salts
(TPEPy-1 to TPEPy-4) possessing different alkyl chains are synthesized,
and the influence of chain length on their optical performance and
applications is thoroughly investigated. By changing the alkyl chain,
the fluorogens exhibit opposite emission behavior in aqueous media
because of their distinct hydrophobic nature, and their solid-state
emission can be fine-tuned from green to red owing to their distinct
molecular configuration. In addition, by increasing the chain length,
the microstructure of the self-assembled fluorogens converts from
microplates to microrods with various emission colors. Moreover, TPEPy-1
exhibits dual-mode fluorescence “turn-on” response toward
NO3– and ClO4– in aqueous media because the anions induce the self-assembly of
fluorogens. Furthermore, the fluorogens display cellular uptake selectivity
while the proper alkyl chain impels the fluorogens to penetrate the
cell membrane and accumulate in the mitochondria with high specificity.