Ionic aggregation-induced emission dye with bulky counterions for preparation of bright near-infrared polymeric nanoparticles

Abstract

Bulky hydrophobic counterions were found to be crucial for the preparation of AIEgen-loaded polymeric nanoparticles with bright NIR emission.

Ionic Aggregation‐Induced Emission: Bulky Hydrophobic Counterions Light Up Dyes in Polymeric Nanoparticles

“…On the other hand, it differs from the previously described ion-association approach, which normally use highly fluorescent dyes such as rhodamine [57] and cyanine [52,78] . Some reports showed that poorly fluorescent cationic dyes could enhance their fluorescence with addition of TPB counterions, [50,52] but here we show that this phenomenon can be observed for both AIE and non-AIE fluorophores. However, the limitation of NPs based on neat dye salts is their tendency to dissolve in hydrophobic compartments of cells leading to dye leakage, as it was shown for rhodamine B -R18 salts with [F5-TPB] and [F12-TPB] counterions.…”

“…This additive effect is very important for design of highly emissive materials and it is supported by our recent work, where emissive properties of an AIEgen could be further improved by using these bulky counterions. [50] In the absorption spectra of the SP dye salts, some hypochromism was still observed compared to the acetonitrile solutions, especially for EtSP18 (Figs. S10-S12).…”

“…[48] Moreover, AIEgens are dominated by neutral molecules, whereas the examples of intrinsically charged AIEgens are very rare. [49,50] Charged fluorophores, bearing cationic (or anionic) groups involved in the electronic conjugation, such as cyanines and rhodamines, [51] are particularly attractive because they are characterized by strong electronic delocalization leading to fluorophores of high extinction coefficient and fluorescence quantum yield. However, these dyes are among the most prone to ACQ because they are extended pi-conjugated structures.…”

“…Recently, we showed that counterions can improve emission properties of AIEgens, especially in the dye-loaded polymeric NPs. [50] In this respect, the current challenge is to apply this bulky counterion approach to produce AIE phenomenon for dyes that intrinsically do not exhibit AIE behavior. In literature, several types of dyes, poorly emissive in organic solvents, have been shown to enhance their emission after association with bulky anions in aqueous media.…”

Recent Advances in Polymeric Nanoparticles for Enhanced Fluorescence and Photoacoustic Imaging

“…Theo riginal idea behind using bulky counterions to prevent the formation of non-fluorescent aggregates was to space the cationic dyes apart in the polymeric core.I nterestingly,A darsh and Klymchenko demonstrated that this concept could also be used to improve the properties of AIEgens, which do not require spatial separation for them to be fluorescent. [42] By exchanging cationic AIEgens initially having small counterions (e.g.h exafluorophosphatea nd perchlorate) with bulky hydrophobic counterions (e.g. FTPBs), followed by encapsulation in apolymer,the authors showed smaller NPs (ca.…”