An effective and facile synthesis of new blue fluorophores on the basis of an 8-azapurine core

Isoxazolyl-Derived 1,4-Dihydroazolo[5,1-c][1,2,4]Triazines: Synthesis and Photochemical Properties

New fluorescent dyes containing an assembled 1,4-dihydroazolo[5,1-c][1,2,4]triazine (DAT) core and an isoxazole ring were synthesized through a reaction between diazopyrazole or diazoimidazoles and isoxazolyl-derived enamines in mild conditions. The photophysical characteristics (maxima absorption and emission, Stokes shifts, fluorescent quantum yields, and fluorescence lifetimes) of the new fluorophores were obtained. The prepared DATs demonstrated emission maxima ranging within 433-487 nm, quantum yields within 6.1-33.3%, and a large Stokes shift. The photophysical characteristics of representative DAT examples were studied in ten different solvents. Specific (hydrogen bonds) and non-specific (dipole-dipole) intermolecular and intramolecular interactions were analyzed using XRD data and spectral experiments. Solvatochromism was analyzed using Lippert-Mataga and Dimroth-Reichardt plots, revealing the relationship between the DAT structure and the nature of solute-solvent interactions. The significant advantages of DATs are the fluorescence of their powders (QY up to 98.7%). DAT-NMe₂10 expressed bright aggregation-induced emission (AIE) behavior in DMSO and THF as the water content increased. The numerous possible variations of the structures of the heterocycles included in the DATs, as well as substituents, create excellent prospects for adjusting their photophysical and physicochemical properties.

Photophysics, photochemistry and bioimaging application of 8-azapurine derivatives

New 2-aryl-1,2,3-triazolopyrimidines were designed, synthesized, and characterized. Their optical properties were thoroughly studied in the solid phase, in solution and in a biological environment. Density Functional Theory (DFT) based calculations were performed, including the molecular geometry optimization for both the ground state and the first singlet excited state, the prediction of the UV-Vis absorption and fluorescence spectra, the determination of the molecular electrostatic properties and the solvent effect on the optical properties. The emission intensity was revealed to increase in time upon irradiation. Mass spectrometric research, quantum mechanical calculations, and analysis of literature data suggested a possible photo-transformation pathway through the homolytic cleavage of one of the C-Cl bonds upon irradiation with UV light. The structure of the active intermediate was identified by the series of mass spectrometry experiments and via synthesis of putative transformation products. The kinetic parameters measured in different solvents allowed estimating the rate of these photo-transformations. Biological experiments demonstrated that 2-aryl-1,2,3-triazolopyrimidines penetrate cells and selectively accumulate in the cell membrane and the Golgi complex and endoplasmic reticulum. Their unique properties pave the way for new possible applications of fluorescent 8-azapurines in biology and medicine.

Synthesis of blue light emitting heterocycles via cyclization of 2-pyridine derived 4-azido-r1,2,3-triazoles

An efficient synthesis of 2-pyridine derived 4-azido-1,2,3-triazoles was elaborated using the corresponding dichlorodiazadienes as precursors. The reaction of the prepared 2-azine substituted diazadienes with sodium azide permits the preparation of target triazoles isolated in up to 92% yield. Subsequent thermal cyclization was studied. Elimination of molecular nitrogen promoted the cyclization of nitrene at the azine nitrogen. As a result, a family of 2H-[1,2,3]triazolo[4',5':3,4]pyrazolo[1,5-a]pyridin-5-ium-4-ides was prepared. The synthesized compounds are members of a new heterocyclic system. Moreover, these compounds are new attractive blue light emitting molecules.

Benzimidazoazapurines: Design, Synthesis, and Photophysical Study

A highly efficient approach to a new class of polycyclic 8-azapurines, benzo[4,5]imidazo[1,2-a][1,2,3]triazolo[4,5-e]pyrimidines (BITPs), with good photophysical characteristics is proposed. The approach comprises condensation of aminobenzimidazoles with 3-oxo-2-phenylazopropionitrile to form 3-(arylazo)benzo[4,5]imidazo[1,2-a]pyrimidine-4-amines, which undergo oxidative cyclization by the catalytic action of copper(II) acetate, resulting in BITPs with 73-84% yield. Spectral investigations demonstrated the fluorescent properties of BITPs, exhibiting good quantum yields (up to 60%) with maxima absorption at 379-399 and emission at 471-505 nm.

Thioarylmaleimides: accessible, tunable, and strongly emissive building blocks

A series of thioarylmaleimides was synthesized to investigate how variation of the thioaryl group can be used to control absorption and emission properties in solution and in the solid-state. Fine-tuning of the photochemical properties was found to be possible using this strategy, and a rainbow of colours and emission wavelengths are accessible in a single step from commercially available compounds.