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Two series of novel [1,2,4]triazolo[4,3-c]- and [1,2,4]triazolo[1,5-c]quinazoline fluorophores with 4′-amino[1,1′]-biphenyl residue at position 5 have been prepared via Pd-catalyzed cross-coupling Suzuki–Miyaura reactions. The treatment of 2-(4-bromophenyl)-4-hydrazinoquinazoline with orthoesters in solvent-free conditions or in absolute ethanol leads to the formation of [4,3-c]-annulated triazoloquinazolines, whereas [1,5-c] isomers are formed in acidic media as a result of Dimroth rearrangement. A 1D-NMR and 2D-NMR spectroscopy, as well as a single-crystal X-ray diffraction analysis, unambiguously confirmed the annelation type and determined the molecular structure of p-bromophenyl intermediates and target products. Photophysical properties of the target compounds were investigated in two solvents and in the solid state and compared with those of related 3-aryl-substituted [1,2,4]triazolo[4,3-c]quinazolines. The exclusion of the aryl fragment from the triazole ring has been revealed to improve fluorescence quantum yield in solution. Most of the synthesized structures show moderate to high quantum yields in solution. Additionally, the effect of solvent polarity on the absorption and emission spectra of fluorophores has been studied, and considerable fluorosolvatochromism has been stated. Moreover, electrochemical investigation and DFT calculations have been performed; their results are consistent with the experimental observation. [ABSTRACT FROM AUTHOR]

Amino-[1,1′]-biphenyl-containing 3-aryl-[1,2,4]triazolo[4,3-c]quinazoline derivatives with fluorescent properties have been designed and synthesized. The type of annelation of the triazole ring to the pyrimidine one has been unambiguously confirmed by means of an X-ray diffraction (XRD) method; the molecules are non-planar, and the aryl substituents form the pincer-like conformation. The UV/Vis and photoluminescent properties of target compounds were investigated in two solvents of different polarities and in a solid state. The samples emit a broad range of wavelengths and display fluorescent quantum yields of up to 94% in toluene solutions. 5-(4'-Diphenylamino-[1,1′]-biphenyl-4-yl)-3-(4-(trifluoromethyl)phenyl)-[1,2,4]triazolo[4,3-c]quinazoline exhibits the strongest emission in toluene and a solid state. Additionally, the solvatochromic properties were studied for the substituted [1,2,4]triazolo[4,3-c]quinazolines. Moreover, the changes in absorption and emission spectra have been demonstrated upon the addition of water to MeCN solutions, which confirms aggregate formation, and some samples were found to exhibit aggregation-induced emission enhancement. Further, the ability of triazoloquinazolines to detect trifluoroacetic acid has been analyzed; the presence of TFA induces changes in both absorption and emission spectra, and acidochromic behavvior was observed for some triazoloquinazoline compounds. Finally, electronic-structure calculations with the use of quantum-chemistry methods were performed for synthesized compounds. [ABSTRACT FROM AUTHOR]

A convenient method for the synthesis of new highly in non-polar solvents soluble photoactive pentafluorophenyl-substituted and extended alkoxyphenyl-substituted 2,2′-bipyridines is reported. The synthetic strategy for the preparation of such ligands involves a sequence of several structural transformations, such as O-alkylation, nucleophilic substitution of hydrogen (SNH) in 1,2,4-triazine precursors via the 'addition–elimination' scheme, and the subsequent conversion of the obtained 1,2,4-triazines into 2,2′-bipyridines by means of the aza-Diels–Alder reaction. The photophysical properties of the synthesized novel pentafluoroaryl-substituted 2,2′-bipyridines were comprehensively studied. The obtained photophysical data indicate the competitive advantages of the herein reported pentafluoroarylated push–pull fluorophores, bearing extended aliphatic moieties, over their analogues containing benzoxy or phenolic fragments in terms of improvement in quantum yield and well-pronounced positive solvatochromism confirmed by the mathematical analysis according to the Lippert–Mataga equation. [ABSTRACT FROM AUTHOR]

Abstract New unsymmetrically substituted 5,5′-diaryl-2,2′-bypiridine "push-pull" fluorophores were prepared in good yields via the "1,2,4-triazine method"/Suzuki coupling reaction sequence. The obtained fluorophores contain the "push-pull" system with donor and acceptor moieties arranged in a D-π-A-π-D fashion, and that provides both the prospective photophysical properties and unique solvatocromic effects for the most representative compounds. Graphical abstract Image 1 Highlights • Synthesis of unsymmetrically substituted 5,5′-diaryl-2,2′-bipyridine fluorophores. • "1,2,4-Triazine" methodology and cross-coupling reactions were done. • Photophysical studies of the present reported fluorophores were investigated. • Single crystal X-ray diffraction studies were performed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fluorine-containing 2-azinyl derivatives of 4-(4-aminoaryl)quinazolines were designed. • 2,4-Disubstituted quinazolines demonstrated positive emission solvatochromism. • Introduction of additional fluorine atom results in bathochromic shift of emission band. • Two-photon absorption in MeCN with δ 2PA in the range of 18.9–227.8 GM was observed. • DFT calculations were carried out to compare monofluoro and difluoro counterparts. Herein, we present design, synthesis and photophysical properties of fluorinated 2-pyridyl and 2-pyrimidinylquinazolines bearing electron donating aminoaryl moiety at the position 4. The described compounds are synthesized in three steps starting from 2-cyanoazine and fluorinated anthranilic acid. The structures of the target compounds are confirmed by NMR spectroscopy, mass spectrometry as well as X-ray diffraction analysis. The photophysical characteristics are investigated in toluene and MeCN. In case of Et 2 N- and Ph 2 N-derivatives the quantum yields increase when going from MeCN to toluene and reach 87 %, whereas emission intensity of carbazolyl counterparts reduces with the decrease in solvent polarity. All the compounds exhibit considerable sensitivity to solvent polarity and change their emission color from blue to red–orange. Additionally, the 2,4-disubstituted fluorophores display two-photon absorption in MeCN with δ 2PA in the range of 18.9–227.8 GM. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coumarin-pyridine fluorophores were obtained via C-H functionalization and Boger reaction. • 4-Alkylcoumarin fluorophores have emission and absorption maxima at 402–415 and 210–307 nm, respectively. • Obtained 4-alkylcoumarin fluorophores are characterized by quantum yields of 6–19%. • Derivatives of 4-phenylcoumarin did not exhibit any noticeable fluorescence. A series of coumarin-pyridine-based push-pull fluorophores were prepared starting from 1,2,4-triazines by using direct C-H functionalization (S N H-reaction)–Diels-Alder–retro Diels-Alder domino reaction sequence. This efficient synthetic strategy allowed to obtain a series of 19 coumarin-pyridine fluorophores. Their photophysical properties were studied. While pyridine-substituted derivatives of 4-alkylcoumarins may be considered as alternative to coumarin dyes characterized by emission maxima mainly in a visible region with wavelengths of 402–415 nm, absorption in the UV range at 210–307 nm, and good photoluminescence quantum yields of 6–19%, all the derivatives of 4-phenylcoumarin did not exhibit any noticeable fluorescence. More detailed photophysical studies were carried out for two the most representative derivatives of 4-alkyl-coumarin-pyridines to demonstrate their positive solvatochromism, and the collected data were analyzed by using Lippert-Mataga equation, as well as Kosower and Dimroth/Reichardt scales. The obtained results demonstrate that the combining two chromophore systems, such as 2,5-diarylpyridine and coumarin ones, is promising in terms of improving the photophysical properties of the new coumarin-pyridine hybrid compounds. [ABSTRACT FROM AUTHOR]