Aggregation-Induced Fluorescence Emission Properties of Dicyanomethylene-1,4-dihydropyridine Derivatives

Abstract

A series of dicyanomethylene-1,4-dihydropyridine (DCMP) derivatives with aggregation-induced emission (AIE) were designed and synthesized. These target compounds emit low fluorescence in THF solutions because of the free rotation of the phenyl and dihydropyridine rings about the axes of the olefinic double bonds and the resultant nonradiative decay process, but they exhibit strong fluorescence in the aggregate state because of the restriction of intramolecular rotation (RIR), as confirmed by solution thickening and cooling experiments. Compared with the almost-planar dicyanomethylene-4H-pyran (DCM) derivative DCM-1 with aggregation-caused quenching (ACQ), DCMP-5 with AIE takes a highly twisted conformation by replacing the oxygen atom of the DCM skeleton with an N-ethyl group, as revealed by crystallographic data and theoretical calculations. Depending on the different electron-donating substituents, the solids of these compounds emit yellow or orange fluorescence. Moreover, the cyano group endows DCMP-5 with a strong self-assembly ability under proper conditions, and the obtained regular microparticles emit bright orange fluorescence. These materials will broaden the new family of AIE-exhibiting fluorophores.

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

“…As shown in Figure A, when NDHP was dissolved in ethanol, the ethanol solution (10.0 μmol L −1 ) hardly emitted any fluorescence. This was likely to be due to the non‐radiative decay of the excited states through the intramolecular free rotations of the 1,4‐dihydropyridine and naphthalene around the double bonds . Increasing the f w from 0 to 50 % resulted in no significant change in the fluorescence intensity.…”

“…Importantly, some 1,4‐dihydropyridine derivatives reportedly exhibit outstanding AIE properties and emit good solid‐state fluorescence upon a simple structural modification. Specifically, an appropriate structural unit introduced on the nitrogen atom of the 1,4‐dihydropyridine ring can lead to twisted molecular conformations . 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.…”

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

“…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.…”

“…2a), meanwhile, there was an obvious leveled-off tail in the visible region due to light-scattering effect because of the formation of nanoscopic aggregates [40]. The pure THF solution of DHP-1 emitted weak green light, which was ascribed to the free rotation of the phenyl ring and DHP ring around the CeC bond facilitating a non-radiative relaxation process [1,23]. As water was gradually added to the THF solution, the dissolved molecules began to aggregate with a RIR process resulting in the enhancement of the fluorescence (Fig.…”

“…However, DCM-1 (Scheme 1), which contains 4-(dimethylamino)styryl group, exhibits aggregation-caused quenching because the strong pushepull interactions associated with the aminoecyano pairs lead to its fluorescence emission quenching owing to nonradiative relaxations of its ICT states [19]. 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].…”