RESUMEN

Experimental and theoretical study of the regioselectivity and mechanism of polycyclic aromatic amine (PAA) electrochemical oxidation is important for designing nitrogen doped large π-conjugated functional molecules. Herein, we used binary-, ternary-, and quaternary-fused PAAs as electro-oxidative reaction substrates to investigate the yield changes of carbazole and phenazine based aza-helicene other than oligomers, which were obtained through pyrrole and pyrazine annulation pathways. Combined with the restrained electrostatic potential (RESP) and steric hindrance factor analysis of the substrate, the electron spin density distribution of free radical resonance hybrid and the spin population analysis of the atoms in the structure of each free radical tautomer indicate that the degree of delocalized dispersion of N free radical and the resulting change in the spin density distribution of C free radical tautomers determine the reaction regioselectivity. The potential charge of the K-region, Bay-region, and L-region adjacent to the C(α)-C(ß1) bond is higher than that of other regions within the molecule, and the charge in these high RESP regions tends to delocalize more strongly toward electron-deficient N free radicals. Thus, the activity of N-C(α)-C(ß1) region is increased, which supports the proposed free radical addition and free radical coupling mechanism for the electro-oxidative reaction of PAA.

RESUMEN

We have developed an efficient modular asymmetric synthesis of azahelicenes through an organocatalyzed asymmetric multicomponent reaction from readily available polycyclic aromatic amines, aldehydes, and (di)enamides, by employing a central-to-helical chirality conversion strategy. A series of aza[5]- and aza[4]helicenes bearing various substituents were readily afforded through this one-pot sequential enantioselective Povarov reaction/oxidative aromatization process, with good yields and high enantioselectivities. The fruitful and diverse derivatizations of the chiral azahelicene products demonstrated the potential of this method, and a preliminary application of the azahelicene derivative as a chiral organocatalyst was showcased. The photophysical and chiroptical properties of these azahelicenes, particularly the acid/base-triggered switching of these properties, were also well studied, which may find potential applications in the development of novel organic optoelectronic materials.

RESUMEN

Functionalization, namely the introduction of side groups onto the molecular scaffold of a helicene, may have either the purpose of modifying the electronic properties of the parent helicene, e.g., by adding electron-withdrawing or electron-donating groups, or the scope of providing the helicene with a "handle", which can be reacted to bind the molecule to another molecule or to a solid structure, such as a carbon or metal surface, or again to allow for complexation of the helicene with metal ions. The possible approaches are two-fold: the synthesis of the helicene can be performed using starting materials that already contain a side group, or the side group can be introduced after the synthesis of the parent helicene. As azahelicenes are helicenes bearing one or more nitrogen atom(s) in the molecular framework, parent azahelicenes can be functionalized on carbon atoms by exploiting the presence of the electron-withdrawing nitrogen atom. Moreover, they can be transformed into quaternary salts, whose properties are quite different from those of the parent azahelicenes in terms of the solubility and electronic properties. This review aims to provide a survey of the different synthetic methods available to attain this fascinating class of compounds.

Asunto(s)

RESUMEN

Nonaqueous capillary electrophoresis (NACE) using methanol (MeOH) as a solvent of the BGEs and quantum mechanical density functional theory (DFT) have been applied to determine the thermodynamic acidity (ionization) constants (pKa ) of mono- and diaza[5]helicenes, mono- and diaza[6]helicenes, and their dibenzo derivatives in MeOH and water. First, the mixed acidity constants, pKa,MeOHmix${\rm{p}}K_{{\rm{a,MeOH}}}^{{\rm{mix}}}$ , of ionogenic pyridinium groups of azahelicenes and their derivatives in MeOH were obtained by nonlinear regression analysis of pH dependence of their effective electrophoretic mobilities. The effective mobilities were measured by NACE in a large series of methanolic BGEs within a wide conventional pH range (pHMeOH 1.6-12.0) and at ambient temperature (21-26°C) in a home-made CE device. Prior to mixed acidity constant calculation, the effective mobilities were corrected to reference temperature (25°C) and constant ionic strength (25 mM). Then, the mixed acidity constants were recalculated to the thermodynamic acidity constants pKa,MeOH by the Debye-Hückel theory of nonideality of electrolyte solutions. Finally, from the methanolic thermodynamic pKa,MeOH values, the aqueous thermodynamic pKa,H2O${\rm{p}}{K_{{\rm{a,}}{{\rm{H}}_{\rm{2}}}{\rm{O}}}}$ constants were estimated using the empirical relations between methanolic and aqueous acidity constants derived for structurally related pyridine derivatives. Depending on the number and position of the nitrogen atoms in their molecules, the analyzed azahelicenes were found to be weak to moderate bases with methanolic pKa,MeOH in the range 2.01-8.75 and with aqueous pKa,H2O${\rm{p}}{K_{{\rm{a,}}{{\rm{H}}_{\rm{2}}}{\rm{O}}}}$ in the range 1.67-8.28. The thermodynamic pKa,MeOH obtained by the DFT calculations were in a good agreement with those determined experimentally by NACE.

Asunto(s)

RESUMEN

Treatment of 11,12-bis(1,1'-biphenyl-3-yl or 6-phenylpyridin-2-yl)-substituted 11,12-dihydro-indolo[2,3-a]carbazole with an oxidizing system of Pd(II)/Ag(I) induced effective double dehydrogenative cyclization to afford the corresponding π-extended azahelicenes. The optical resolutions were readily achieved by a preparative chiral HPLC. It was found that the pyridopyrrolo-carbazole-based azahelicene that contains four nitrogen atoms exhibits ca. 6 times larger dissymmetry factors both in circularly dichroism (CD) and circularly polarized luminescence (CPL), |gCD | and |gCPL | values being 1.1×10-2 and 4.4×10-3 , respectively, as compared with the parent indolocarbazole-based azahelicene. Theoretical calculations at the RI-CC2 level were employed to rationalize the observed enhanced chiroptical responses. The (chir)optical properties of the former helicene was further tuned by a protonation leading to remarkable red-shift with a considerable enhancement of the |gCPL | value.

RESUMEN

Configurationally stable 5-aza[6]helicene (1) was envisaged as a promising scaffold for non-conventional ionic liquids (IL)s. It was prepared, purified, and separated into enantiomers by preparative HPLC on a chiral stationary phase. Enantiomerically pure quaternary salts of 1 with appropriate counterions were prepared and fully characterized. N-octyl-5-aza[6]helicenium bis triflimidate (2) was tested in very small quantities as a selector in achiral IL media to perform preliminary electrochemical enantiodifferentiation experiments on the antipodes of two different chiral probes. The new organic salt exhibited outstanding enantioselection performance with respect to these probes, thus opening the way to applications in the enantioselective electroanalysis of relevant bioactive molecules.

Asunto(s)

RESUMEN

The oxidative photocyclization of aromatic Schiff bases was investigated as a potential method for synthesis of phenanthridine derivatives, biologically active compounds with medical applications. Although it is possible to prepare the desired phenanthridines using such an approach, the reaction has to be performed in the presence of acid and TEMPO to increase reaction rate and yield. The reaction kinetics was studied on a series of substituted imines covering the range from electron-withdrawing to electron-donating substituents. It was found that imines with electron-withdrawing substituents react one order of magnitude faster than imines bearing electron-donating groups. The 1H NMR monitoring of the reaction course showed that a significant part of the Z isomer in the reaction is transformed into E isomer which is more prone to photocyclization. The portion of the Z isomer transformed showed a linear correlation to the Hammett substituent constants. The reaction scope was expanded towards synthesis of larger aromatic systems, namely to the synthesis of strained aromatic systems, e.g., helicenes. In this respect, it was found that the scope of oxidative photocyclization of aromatic imines is limited to the formation of no more than five ortho-fused aromatic rings.

Asunto(s)

RESUMEN

Three azahelicene derivatives with electron-rich bis(4-methoxyphenyl)amino or bis( p-methoxyphenyl)aminophenyl groups at the terminals were deliberately designed, synthesized, and characterized as hole-transporting materials (HTMs) for perovskite solar cells (PSCs). Optical and thermal properties, energy level alignments, film morphologies, hole extraction ability, and hole mobility were studied in detail. PSCs using the newly synthesized molecules as HTMs were fabricated. A maximum power conversion efficiency (PCE) of 17.34% was observed for the bis( p-methoxyphenyl)amino-substituted derivative (SY1) and 16.10% for the bis( p-methoxyphenyl)aminophenyl-substituted derivative (SY2). Longer-chain substituent such as hexyloxy group greatly diminishes the efficiency. In addition, the dopant-free devices fabricated with SY1 as the HTM shows an average PCE of 12.13%, which is significantly higher than that of spiro-OMeTAD (7.61%). The ambient long-term stability test revealed that after 500 h, the devices prepared from SY1 and SY2 retained more than 96% of its initial performance, which is much improved than the reference device with standard spiro-OMeTAD as the HTM under the same conditions. Detailed material cost analysis reveals that the material cost for SY1 is less than 8% of that for spiro-OMeTAD. These results provide a useful direction for designing a new class of HTMs to prepare highly efficient and more durable PSCs.

RESUMEN

The enantioselective synthesis of an aza[10]helicene, possessing two pyridone units, has been achieved by the gold-catalyzed intramolecular quadruple hydroarylation of a tetrayne. This aza[10]helicene was successfully converted into a fully aromatic aza[10]helicene, possessing two pyridine units. Structure-photophysical and chiroptical properties relationship in a series of azahelicene isomers has also been disclosed.

RESUMEN

A facile and moderately functional-group-tolerant synthetic method for the preparation of 7,8-diaza[5]helicenes has been developed. It comprises of an oxidative ring-closing process of 1,1'-binaphthalene-2,2'-diamine (BINAM) derivatives with a chlorine-containing oxidant (t-BuOCl) in the presence of a base (2,6-lutidine). In addition the basic physicochemical properties of newly synthesized compounds have been investigated.

RESUMEN

Driving benzene round the twist: Azahelicene derivatives were synthesized in high yields by utilizing palladium-catalyzed C-H annulation reactions. Functionalization at the C5 position in 6-azahelicene by using palladium-catalyzed C-H arylation also gave coupling products in good yields. A tandem intra- and intermolecular double C-H coupling reaction was performed to give a functionalized helicene in a one-pot procedure.