Rational Design of a Red-Emissive Fluorophore with AIE and ESIPT Characteristics and Its Application in Light-Up Sensing of Esterase

Abstract

The development of red fluorophores with efficient solid-state emission is still challenging. Herein, a red fluorophore 1 with aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics is rationally designed and facilely synthesized by attaching an electron-donor diethylamine and an electron-acceptor maleonitrile group to salicyladazine. In contrast to many red fluorophores which undergo serious aggregation-caused quenching (ACQ), compound 1 emits bright red fluorescence (λ = 650 nm, Φ = 24.3%) in the solid state with a large Stokes shift of 174 nm. Interestingly, control compounds 2 and 3, which have similar structures as 1, exhibit obvious aggregation-caused quenching (ACQ) characteristics. The difference in the crystal structures of 1, 2, and 3 reveals that the interplanar spacing among molecules plays a decisive role in realizing the AIE characteristics of 1. Moreover, when the hydroxyl group of 1 was substituted by an esterase reactive acetoxyl, a fluorescence light-up probe 4 was developed for sensing of esterase based on the selective reaction between 4 and esterase to generate the AIE and ESIPT active molecule 1. The linear range for in vitro quantification of esterase is 0.01-0.15 U/mL with a detection limit of 0.005 U/mL. Probe 4 was also successfully applied to image esterase in mitochondria of living cells.

Theoretical insights into excited‐state process for the novel 2,3‐bis[(4‐diethylamino‐2‐hydroxybenzylidene)amino]but‐2‐enedinitrile system

“…Thus, we mainly explore the photochemical and photophysical properties in the S 1 state. As shown in Table , we list that the calculated absorption peak (S 0 → S 1 ) is located at 588 nm, which is in agreement with the previous experimental result of 547 nm . It confirms that the theoretical level TDDFT/B3LYP/TZVP we adopted is reasonable for this system in this work.…”

“…Very recently, Peng et al synthesized a novel fluorophore 2,3‐bis[(4‐diethylamino‐2‐hydroxybenzylidene)amino]but‐2‐enedinitrile (BDABE), which contains two intramolecular hydrogen bonds. Based on BDABE molecule and its derivatives, authors explored the aggregation‐induced emission and aggregation‐caused quenching aspects via experimental manners.…”

Tuning Emission Wavelength of Polymorphous Crystal via Controllable Alkyl Chain Stacking and Its Vapor‐ and Thermo‐Responsive Fluorescence

“…The AIE effect of BA‐C16 occurs when the water volume fraction in the co‐solvent is more than 20 % and fluorescence intensity could be further enhanced with higher water volume fractions, which correlates well with the increased aggregate formation in poorer solvents. The AIE fluorescence originates from the restriction of free intramolecular rotation, assisted by intramolecular hydrogen bonds of BA‐C16 in the aggregate state and from the excited state intramolecular proton transfer (ESIPT) …”

Organic Mitoprobes based on Fluorogens with Aggregation‐Induced Emission

“…TPE-Ph-In is the first non-self-quenching probe that could monitor the membrane potential change of mitochondria. [76] Probe 4 contains an esterase responsive acetoxyl group and exhibits very weak fluorescence in aqueous solutions. Since the targeting of TPE-Ph-In to mitochondria depends on its membrane potential, which promotes the accumulation of dyes in normal condition, after incubating HeLa cell with TPE-Ph-In, the membrane potential change could be monitored by its fluorescence variation when the cells were treated with oligomycin or carbonyl cyanide 3-chlorophenylhydrazone to increase or decrease the membrane potential, respectively ( Figure 6C).…”