Microwave synthesis of fluorescent and luminescent dyes (1990–2017)

New Luminescent Pyridine-based Disc type Molecules: Synthesis, Photophysical, Electrochemical, and DFT studies

The design and synthesis of new conjugated luminescent molecules have attracted the attention of researchers because of their various applications, especially in the field of optoelectronic devices. Most of the applications were mainly based on the intramolecular charge transfer (ICT). For this purpose, we designed and synthesized a series of new donor-acceptor based disc type molecules i.e. 2,4,6-tris(4-(alkyloxy)phenyl)pyridines carrying variable alkoxy chains [i.e. n = 2, 4, 6, 8, 10, 12, 14, 16]. Further, the structures of all the synthesized compounds were confirmed by using ATR-IR, ¹H-NMR, ¹³C-NMR, and ESI-MS analysis. Moreover, the photophysical property study indicated that all the molecules are blue light emitting materials, however the change of alkoxy chain length in phenyl arms does not affect their absorption, emission, and energy levels. Besides, the thermal study revealed that core is stable up to 350 °C. Also, the DFT study showed that the photo induced electron transfer caused by HOMO-LUMO excitation in the studied molecules. Therefore, all the molecules have potential applications in optoelectronic applications.

3-(3-Bromophenyl)-7-acetoxycoumarin

In natural product synthesis, the procurement of easily accessible starting materials is crucial. Chromenones and their subclass, coumarins, are a wide family of small, oxygen-containing aromatic heterocycles. Phenylcoumarins offer a particularly excellent starting point for a diverse chemical space of natural products, and thus are excellent staring materials for more complex natural products. Herein, we report an efficient synthesis of an easily accessible 3-phenylcoumarin bearing two orthogonally substitutable groups, bromine, and an acetyl-protected phenylic hydroxyl group.

Four-Coordinate Monoboron Complexes with 8-Hydroxyquinolin-5-Sulfonate: Synthesis, Crystal Structures, Theoretical Studies, and Luminescence Properties

8-Hydroxyquinolin-5-sulfonic acid (8HQSA) was combined with 3-pyridineboronic acid (3PBA) or 4-pyridineboronic acid (4PBA) to give two zwitterionic monoboron complexes in crystalline form. The compounds were characterized by elemental analysis, single-crystal X-ray diffraction studies, and IR, 1H NMR, UV-Visible, and luminescence spectroscopy. The analyses revealed compounds with boron atoms adopting tetrahedral geometry. In the solid state, the molecular components are linked by charge-assisted (B)(O-H···−O(S) and N+-H···O(S) hydrogen bonds aside from C-H···O contacts and π···π interactions, as shown by Hirshfeld surface analyses and 2D fingerprint plots. The luminescence properties were characterized in terms of the emission behavior in solution and the solid state, showing emission in the bluish-green region in solution and large positive solvatofluorochromism, caused by intramolecular charge transfer. According to TD-DFT calculations at the M06-2X/6-31G(d) level of theory simulating an ethanol solvent environment, the emission properties are originated from π-π * and n-π * HOMO-LUMO transitions.

Synthesis, photophysical properties and theoretical studies of new bis-quinolin curcuminoid BF2-complexes and their decomplexed derivatives

This paper presents the synthesis and characterization of two series of new bis-quinolin curcuminoid BF₂-complexes 11 and their respective decomplexed bis-quinolin curcuminoid derivatives 12, in an attempt to understand their optical properties. The synthesized compounds showed interesting fluorescent characteristics in both solution and in solid-state. The characteristic of the electronic transitions involved in these systems were measured via Uv-vis spectroscopy and fluorescence spectroscopy. Results revealed that the absorption and emission bands are dependent of the structure of compounds 11 and 12 but also of the type of substituent, even showing a push-pull behavior in those derivatives substituted with methyl group. These findings were also confirmed through computational calculations at DFT level via simulations of the Uv-vis spectra and determining the topology of the border orbitals responsible for light absorption.

Microwave-Assisted One-Pot Synthesis of Indole-Based Fluorescent Probe for Sensitive Detection of Copper (II)

In this study, a rapid, inexpensive and convenient microwave assisted synthesis of indole-3-propionic acid-bisphenol A diglycidyl ether (IPA-SR3) fluorescent probe was developed. This fluorescent probe has the dual illumination characteristics of photoinduced electron transfer and aggregation-induced emission for the specific detection of Cu²⁺ ion in water. The wavelength-dependent photoluminescence behavior of the aggregated IPA-SR3 was highly selective (Ksv = 1.5 × 104 M^-1) and sensitive in Cu²⁺ ion detection, with a low limit of detection (2.9 μM). Therefore, it can be used to detect low-concentration Cu²⁺ in water samples. Details of the synthesis procedure and fluorescence characteristics are presented herein. Graphical Abstract.

Green Accelerated Synthesis, Antimicrobial Activity and Seed Germination Test of Quaternary Ammonium Salts of 1,2-bis(4-pyridyl)ethane

A family of fifteen quaternary ammonium salts (QAs), bearing the 1,2-bis(4-pyridyl)ethane core, were obtained using for the first time two different green methods, such as microwave (MW) and ultrasounds (US) irradiation, with very good yields and in much shorter times compared to the classical method, and an assay on their antimicrobial action against Escherichia coli (E. coli) was carried out. While 12 to 24 hours were required for complete alkylation of 1,2-bis(4-pyridyl)ethane by reactive halogenated derivatives in anhydrous solvent under reflux conditions, MW and US irradiation reduced the reaction time and the desired products were achieved in a few min. One of the aims of this study was to evaluate the antibacterial potential of the synthesized QAs against pathogenic bacteria, along with their impact on germination activity of wheat seeds (Triticum aestivum L.). The antibacterial activity of the QAs against Escherichia coli was explored by determining the minimum inhibitory concentration (MIC). The MIC values varied from 0.312 to 2.5 mg/mL, highlighting the lowest values attained for the derivatives containing methoxy, chlorine and benzofurane functional groups. The viability of aerobic bacteria was determined with the Tetrazolium/Formazan Test, a method that was found to be the best alternative approach with respect to the difuzimetric method. Seeds of Triticum aestivum L. were used for the evaluation of the germination indicators, such as seed germination (SG), the relative seed germination (RSG), the relative radicle growth (RRG), and the seed germination index (GI). The toxicity studies of QAs 1, 4 and 7, at two different concentrations, showed no inhibitory effect on seed germination.

Green Methodologies for Copper(I)-Catalyzed Azide-Alkyne Cycloadditions: A Comparative Study

Successful copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions may be achieved by several methods. In this paper, four synthetic protocols were performed for direct comparison of time required for the synthesis, yield, and purity of the 1H-1,2,3-triazole products. The methods with Cu(I) catalysts were conventional, microwave heating, solvent-free, and a method using glycerol solvent. The compounds synthesized in this paper were known non-fluorinated triazoles and new fluorinated triazoles. The results lead to the conclusion that the microwave method should be strongly considered for CuAAC syntheses.

Practical Microwave Synthesis of Carbazole Aldehydes for the Development of DNA-Binding Ligands

Microwave formylation of carbazole derivatives was investigated and 3-monoaldehydes were obtained in high yield. A potential DNA-binding ligand, 3-[(3-ethyl)-2-vinylbenzothiazolium]-9-N-ethyl carbazole iodide, was synthesized and characterized including spectral properties (UV-Vis absorption and fluorescence spectra). The binding selectivity and affinity of three carbazole ligands for double-stranded and G-quadruplex DNA structures were studied using a competitive dialysis method in sodium- and potassium-containing buffer solutions.