Anca Paun

1,3,4-Oxadiazoles as luminescent materials for organic light emitting diodes via cross-coupling reactions

Highly efficient materials for the fabrication of OLEDs have been extensively investigated in terms of properties and convenient synthetic procedures. 2,5-Diaryl-1,3,4-oxadiazoles were found to display suitable structural features in order to act as good electron-transporters, and numerous research groups have focused on the synthesis of various small-molecules and polymers bearing this heterocyclic moiety. Characterisation of their optical and electronic properties indicated the oxadiazole derivatives as good candidates for the fabrication of electroluminescent devices. Chemical synthesis of compounds containing a variety of heterocyclic cores and functional organic groups has witnessed a tremendous evolution concomitant with the development of metal-catalysed cross-coupling reactions. This new approach to create molecular diversity was also observed in the field of oxadiazoles, in an attempt to prepare complex molecules whose structural particularities were able to furnish the properties required for the fabrication of functional materials. Herein, we describe a collection of literature studies that refer to 1,3,4-oxadiazole-based small-molecules and polymers that have found applications as materials for OLEDs, combined with their synthetic accesibility involving, as key step(s), cross-coupling reactions.

Synthesis and biological activities of some new isonicotinic acid 2-(2-hydroxy-8-substituted-tricyclo[7.3.1.02.7]tridec-13-ylidene)-hydrazides

A series of several new isoniazid derivatives, isonicotinic acid 2-(2-hydroxy-8-substituted-tricyclo[7.3.1.0(2.7)]tridec-13-ylidene)-hydrazides, were synthesized and fully characterized. These new isoniazid derivatives were studied regarding their antibacterial activity and cytotoxicity, as well as their influences on some metabolizing enzymes. The best anti-mycobacterial activity was observed in the case of compounds containing alkyl side chains in the 8 position of tricyclo[7.3.1.0(2.7)]tridec-13-ylidene group. On contrary, the antimicrobial activity of these new compounds against various non-tuberculosis strains showed the best activity to be with the phenyl side chain of compound 6. It proved also to be the most toxic, inducing apoptosis and blocking the cell cycle in G0/G1 phase. The cell cycle was blocked in G0/G1 phase also by compound 3, but this compound did not show any toxicity. All compounds induced the expression of NAT1 and NAT2 genes in HT-29 cell line, and the expression of CYP1A1 in HT-29 and HCT-8 cell lines. The expression level of CYP3A4 was increased by compounds 1, 6 and 7 in HCT-8 cells. These results indicated that the activation of other metabolizing pathways, apart from those of isoniazid, take place. It might also point out the possibility of an increased isoniazid acetylation ratio by co-administration with new compounds in slow acetylators.

Chemical and biological evaluation of some new antipyrine derivatives with particular properties.

Starting from 4-amino-antipyrine, six new compounds were synthesized and characterized. The new compounds contain moieties with particular properties, such are ionophore (benzo-15-crown-5), fluorescent (nitrobenzofurazan), stable free radical (nitroxide), or other types of biological active residues, like nitroderivatives, antipyrine or isoniazid residues. They were fully characterized by appropriate means ((1)H and (13)C NMR, IR, UV-Vis, fluorescence, EPR, elemental analysis) and some of their biological properties were evaluated. Hydrophobicity (R(M0), log P), total antioxidant capacity (TAC), and antimicrobial properties are also presented and discussed.

Conformation-induced light emission switching of N-acylhydrazone systems

N-Acylhydrazones have been described as responsive compounds to a wide variety of triggers that are able to induce reversible structural changes. These reversible constitutional, conformational or configurational changes caused by physical or chemical stimuli are useful tools in designing molecular switches. We report herein bis-N-acylhydrazones as new switchable-light emissive molecules triggered by light and/or solvents. The emissive properties could be explained by phototautomerisation (Excited State Intramolecular Proton Transfer) and by formation of aggregates (Aggregation-Induced Emission). We investigated the influence of structural particularities brought in by electron-donor or electron-withdrawing substituents as well as the requirement of several hydrazone bonds in the molecular structure for the generation of light.

CCDC 1547795: Experimental Crystal Structure Determination

Related Article: Anca G. Coman, Codruta C. Paraschivescu, Anca Paun, Andreea Diac, Niculina D. Hădade, Laurent Jouffret, Arnaud Gautier, Mihaela Matache, Petre Ionita|2017|New J.Chem.|41|7472|doi:10.1039/C7NJ01698K

Synthesis of novel profluorescent nitroxides as dual luminescent-paramagnetic active probes

We describe herein the synthesis of new profluorescent nitroxides based on 2,5-disubstituted-1,3,4-oxadiazoles as fluorescent moieties and the 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) as paramagnetic probes. The synthesis and optical and electronic properties of the oxadiazole-based precursors of the profluorescent nitroxides, as well as the nitroxides and their reduced forms are also described. Physical investigations (i.e. absorption and emission spectroscopy, cyclic voltammetry) indicate a different luminescence behaviour function to the oxadiazole substituent. A linear response to reducing agents, i.e. sodium ascorbate, monitored by fluorescence spectroscopy, suggests the possibility of using the synthesized compounds as potent active probes in detection of various analytes of interest.

Long-lived states detect interactions between small molecules and diamagnetic metal ions

Long-lived states of nuclear spin order were used for the first time to probe interactions between molecules and diamagnetic metal ions. Proton spin states with lifetimes twice as long as the spin-lattice relaxation time constants of the same nuclei were promoted on the methoxyphenyl and tolyl substituents of a 1,3,4-oxadiazole derivative. The transient interaction of this oxadiazole derivative with silver(I) ions significantly speeds up the relaxation rate constants of proton long-lived states. The interactions between silver and organic compounds lead to the formation of coordination polymers that can be used for the preparation of bio-compatible materials.

EPR Spectra of a Mono- and a Hetero-Diradical in Nematic and Isotropic Phases

A hybrid hydrazine–nitroxide monoradical and the corresponding heterohydrazyl– nitroxide diradical were used as probes in 4-cyano-4′-pentylbiphenyl liquid crystal. EPR data (hyperfine constants, rotational time, and anisotropy parameter values) are reported in the range of 25°C–55°C. It was shown by EPR spectrometry that the nitroxide moiety gives an anisotropic triplet line, while the hydrazyl moiety cannot be detected under these conditions.