The twisted intramolecular charge transfer (TICT) mechanism and twists beyond TICT have guided the creation of numerous bright and sensitive fluorophores. We reviewed the structure–property relationships of these dyes with representative examples.
Insufficient
brightness of fluorophores poses a major bottleneck
for the advancement of super-resolution microscopes. Despite being
widely used, many rhodamine dyes exhibit sub-optimal brightness due
to the formation of twisted intramolecular charge transfer (TICT)
upon photoexcitation. Herein, we have developed a new class of quaternary
piperazine-substituted rhodamines with outstanding quantum yields
(Φ = 0.93) and superior brightness (ε × Φ =
8.1 × 104 L·mol–1·cm–1), by utilizing the electronic inductive effect to
prevent TICT. We have also successfully deployed these rhodamines
in the super-resolution imaging of the microtubules of fixed cells
and of the cell membrane and lysosomes of live cells. Finally, we
demonstrated that this strategy was generalizable to other families
of fluorophores, resulting in substantially increased quantum yields.
Inhibition of TICT can significantly increase the brightness of fluorescent materials. Accurate prediction of TICT is thus critical for the quantitative design of high‐performance fluorophores and AIEgens. TICT of 14 types of popular organic fluorophores were modeled with time‐dependent density functional theory (TD‐DFT). A reliable and generalizable computational approach for modeling TICT formations was established. To demonstrate the prediction power of our approach, we quantitatively designed a boron dipyrromethene (BODIPY)‐based AIEgen which exhibits (almost) barrierless TICT rotations in monomers. Subsequent experiments validated our molecular design and showed that the aggregation of this compound turns on bright emissions with ca. 27‐fold fluorescence enhancement, as TICT formation is inhibited in molecular aggregates.
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