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A synthetic approach to prepare boron-enriched π-conjugated photoactive molecular systems based on ortho-carborane using the Cu(I)-catalyzed Sonogashira-type coupling reaction has been developed. The obtained luminophores have been found to possess absorption in the range of 300 to 400 nm, emission of up to 700 nm, and photoluminescence quantum yields of up to 99% in non-polar solvents. TD-DFT calculations have demonstrated that the luminophores are characterized by phosphorescent emission behavior with a lifetime of about 7 μs. In addition, the rigidochromism for the synthesized compounds has been revealed; particularly, the transition electronic state and bathochromic shift have been elucidated in the emission spectra. The exhibited luminescent characteristics indicate that the elaborated vinylcarborane fluorophores could be considered as promising building blocks in the design of advanced photofunctional materials for molecular electronics. [ABSTRACT FROM AUTHOR]

Mono- and bis-2-thienyl-substituted 1,3,7-triazapyrenes have been synthesized for the first time via BF3-mediated C–H/C–Li coupling of 1,3,7-triazapyrene with 2-thienyllithium in 33 and 51% yields, respectively. The photophysical properties of these polycyclic azaaromatics have been studied, with emission in the range of 450–500 nm and fluorescence quantum yields of up to 99% in methanol solutions being revealed. The turn-off chemosensing properties of 2-thienyl-substituted 1,3,7-triazapyrenes for the selective detection of nitroaromatics have also been assessed; in particular, the quenching constants according to the Stern–Volmer model, the quenching sphere radius according to the Perrin model, the detection limit and the quenching efficiency have been determined. In particular, 6,8-bis-(thiopen-2-yl)-1,3,7-triazapyrene, characterized by 10 times the quenching constant and limit of detection (LOD) compared to the mono-substituted analog, can be considered as the most promising chemosensor for determining nitroaromatic compounds. DFT calculations confirm the presence of intramolecular charge transfer (ICT) effects in the case of the obtained fluorophores and clarify the quenching mechanism for nitroaromatics. [ABSTRACT FROM AUTHOR]

Azapyrenes are the nitrogen isosteres of pyrene. Based on theoretical and experimental studies, electron–acceptor azapyrene domains may be considered as convenient scaffolds for constructing a large variety of "push–pull" π-conjugated chromophores with pronounced ICT properties. Over the past decade, due to the unrelenting interest in functional materials and modern methodologies such as cross-coupling, peri-annulation, direct C–H-functionalization, etc., methods for the synthesis of aryl(alkyl) K-functionalized azapyrenes and other derivatives have been developed, and their photophysical and electrochemical properties have been studied. This short review aims at critical analysis of the best known/modern methods for the preparation of functionalized azapyrene derivatives, as well as an assessment of their photophysical/electrochemical properties in comparison with the structural and electronic properties of the parent pyrene. [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]

• Pot, atom, and step economy (PASE) strategy towards push-pull fluorophores. • Perfluorophenyl-modified 3-pyridyl-2-yl-1,2,4-triazines and 2,2′-bipyridines. • New fluorinated materials for molecular electronics and medicinal chemistry. An original pot, atom, and step economy (PASE) approach towards novel pentafluorophenyl-substituted 2,2′-bipyridine fluorophores, as well as their triazine precursors via oxidative transition metal-free C H/C Li coupling reactions between 1,2,4-triazines and pentafluorophenyl lithium followed by aza-Diels-Alder reaction has first been reported. This reaction sequence has been found to afford a number of novel pentafluorophenyl-modified heterocyclic ensembles of various architectures, such as perfluorophenyl-substituted 1,2,4-triazines, their dihydro derivatives, as well as 2,2′-bipyridines in good to excellent yields. The photophysical properties of the synthesized bipyridine fluorophores have been studied, and non-linear optics behavior of the most representative fluorophore has been disclosed on the basis of a positive solvatochromism effect observed. The novel fluorinated 2,2′-bipyridines synthesized are of particular interest in the design of advanced materials for molecular electronics and medicinal chemistry. [ABSTRACT FROM AUTHOR]

A series of novel push-pull fluorophores based on 2 H -imidazole scaffold bearing perfluorophenyl substituent and extended electron-donating conjugating π-system were synthesized. In particular, the Pd-catalyzed Suzuki-Miyaura coupling reactions were exploited as a main synthetic strategy to modify 4-(4-bromophenyl)-2,2-dimethyl-5-(pentafluorophenyl)-2 H -imidazole with various electron-donating functionalities. The comprehensive photophysical studies were carried out for the synthesized fluorophores, including the analysis of absorbance and emission spectra and determination of absolute quantum yields. The designed compounds were found to have a strong emission in the range of 470–610 nm depending on both the nature of solvent used and the structure of electron-donating group attached to the aryl moiety. The pH effect of the aqueous-organic mixture buffer solution on the fluorescent characteristics of the synthesized compounds was established and the deprotonation-induced "turn-on" pH sensing mechanism supported by DFT calculations was proposed for the first time. Particularly, the sequence of deprotonation was confirmed, and free energies for all N-protonated and N-proton-free forms were calculated. No toxic effect on the human embryonic kidney cells (HEK-293) at concentration of ≤512 μM was observed in vitro experiments. In addition, new opportunities for the practical application of these molecular ensembles were demonstrated in case of fluorometric determination of the pH both in model solutions and real saliva probes, with 3-(4-(2,2-dimethyl-5-(pentafluorophenyl)-2 H -imidazole-4-yl)phenyl)-9-phenyl-9 H -carbazole being used. [Display omitted] • Push-pull fluorophores with a strong emission in the range of 470–610 and quantum yields up to 96%. • No toxic effects at concentration of ≤512 μM from in vitro experiments. • Advanced "turn-on" fluorescent probes for determining the pH in saliva. [ABSTRACT FROM AUTHOR]

A number of novel fluorinated derivatives of the family of pyrido[1,2- a indole fluorophores have first been synthesized via the aryne-mediated domino transformations of 5-(perfluorophenyl)-3-(pyridin-2-yl)-1,2,4-triazines. A comprehensive study of photophysical properties of the obtained polyfluoroaryl substituted derivatives, in which polyfluoroaryl, 1,2,3-triazole, and pyridoindole subunits contribute to a joint chromophore system, has shown that these compounds proved to exhibit a fluoresce with green light in acetonitrile solutions. Image 1 • Aryne-mediated transformations leading to novel pyrido[1,2- a indoles. • Polyfluorinated 10-(1 H -1,2,3-triazol-1-yl)pyrido[1,2- a indole fluorophores. • Novel green-emitting heteroaromatics with tunable photophysical characteristics. [ABSTRACT FROM AUTHOR]