Multi-Stimulus-Responsive Fluorescent Properties of Donor-π-Acceptor Indene-1,3-dionemethylene-1,4-dihydropyridine Derivatives

Abstract

Three donor (D)-π-acceptor (πA) indene-1,3-dionemethylene-1,4-dihydropyridine (IDM-DHP) derivatives with triphenylamine (TPA)/bis­(diphenylamino)­triphenylamine (BDPA-TPA) end groups were designed and synthesized. These target compounds with highly twisted conformations showed aggregation-induced emission enhancement properties in their THF/water mixtures due to the restriction of intramolecular rotation, and distinct piezofluorochromic (PFC) properties in the solid state. Interestingly, solvent-induced emission changes similar to those resulting from PFC properties can be achieved by a simple dissolution–desolvation process in different solvent systems, such as chloroform, THF, and dichloromethane. X-ray diffraction experiments revealed that the transformations between crystalline and amorphous states were responsible for the PFC properties and solvent-induced emission changes. Moreover, these compounds exhibited remarkable and reversible acid/base-induced fluorescence switching properties in both solution and the solid state. The results indicate that the IDM-DHP derivatives with a TPA/BDPA-TPA unit exhibit intriguing multi-stimulus-responsive fluorescent behaviors. The current study will help researchers to design and synthesize more aggregation-induced emission/aggregation-induced emission enhancement-active multifunctional stimulus-responsive fluorescent materials.

Piezochromism, acidochromism, solvent-induced emission changes and cell imaging of D-π-A 1,4-dihydropyridine derivatives with aggregation-induced emission properties

“…When the original sample of DHP-3 was dissolved in chloroform and then evaporated to dryness using vacuum rotary evaporation, a strong red-emitting solid was obtained (l em max ¼ 626 nm), which was similar to the sample showing piezochromic property and could be ascribed to solvent-induced emission change caused by a simple dissolutionedesolvation process (DDP) [24]. By the same method, red emissive solids were achieved using CH 2 Cl 2 (l em max ¼ 619 nm) as a solvent, but THF had little influence on the color and the l em max of the DDP-THF sample only showed 4-nm red shift (l em max ¼ 602 nm).…”

“…2-(2,6-Dimethyl-4H-pyran-4-ylidene)malononitrile (5a) [23], ethyl 2-cyano-2-(2,6-dimethyl-4H-pyran-4-ylidene)acetate (5b) [39], and 2-(2,6-dimethyl-4H-pyran-4-ylidene)-2H-indene-1,3-dione (5c) [24] were synthesized by the reaction of 2,6-dimethyl-4-pyrone (1) with malononitrile (2), ethyl 2-cyanoacetate (3), and 2H-indene-1,3-dione (4) in acetic anhydride according to the previous literature, respectively. The intermediates 6a¡c were synthesized by the reaction of compounds 5a¡c with n-octylamine in CH 3 CN at 80 C. Then the DHP derivatives were obtained from the Knoevenagel condensation between compounds 6a¡c and 4-(dimethylamino)benzaldehyde in 68e72% yields.…”

“…Very recently, we reported a dicyanomethylene-1,4-dihydropyridine derivative DCMP-1 with remarkable AIE property resulting from the replacement of the oxygen atom of the DCM skeleton with an N-ethyl group, which could effectively promote the distortion of the molecular structure and avoid the fluorescence quenching in the aggregation state [23]. Furthermore, a series of indene-1,3-dionemethylene-1,4-dihydropyridine derivatives with triphenylamine/bis(diphenyl-amino)triphenylamine end groups were found to exhibit AIE characteristics and multifunctional stimuli-responsive fluorescent behavior in the solid state [24].…”

“…The introduction of a long octyl side chain onto the DHP ring not only improves the dissolution properties of these compounds, but also might have a significant effect on their aggregation behaviors in the solid state by changing the molecular backbone conformation and the molecular packing mode, leading to AIE or piezochromism [31e38]. Additionally, when a dimethyl amino group, 1H-indene-1,3(2H)-dione unit and DHP ring were introduced into the molecular structures [24], the acidochromic properties of these compounds was expected through the basic nitrogen/oxygen atoms as the binding sites for the protons. As a result, these target compounds exhibited obvious AIE characteristics, and interestingly, the electron-withdrawing end groups endowed them with different stimuli-responsive fluorescent behaviors in the solid state.…”

Aggregation‐Induced Emission‐Active 1,4‐Dihydropyridine‐Based Dual‐Phase Fluorescent Sensor with Multiple Functions

“…Furthermore, some 1,4‐dihydropyridine derivatives reportedly exhibit solid‐state fluorescence color changes upon external stimuli such as exposure to pressure, acidic vapor, organic vapor, and heat. Namely, they exhibit mechanochromic (MC), acidochromic, vapochromic, and thermochromic properties, respectively . However, 1,4‐dihydropyridine derivatives that exhibit stimulus‐responsive activities in both the solid and solution state are rarely reported.…”