Electron-donating Aryl Groups Research Articles

Photophysical properties of donor–acceptor antiaromatic organoboron compounds based on dithienodiborinines

Abstract Boron-containing antiaromatics, such as diborinines and boroles, have sparked interest in materials chemists owing to their exciting optical properties and high Lewis acidity. In this study, we synthesized donor–acceptor (D–A) type diborinines fused with thiophene rings by introducing electron-donating amino-substituted aryl groups onto boron and elucidated their properties. The D–A type dithienodiborinines exhibited long-wavelength absorption arising from their D–A interactions and antiaromaticity. In addition, their fluorescence intensity increased under oxygen-free conditions, indicating thermally activated delayed fluorescence.

Aggregation-induced phosphorescence emission-active heteroleptic Ir(III) complexes: Synthesis, photophysics, and latent fingerprint detection applications

Three heteroleptic Ir(III) complexes (Ir-TPA, Ir-CzPh and Ir-PhCz) with different electron-donating aryl groups on C^N ligands were synthesized. Their optical properties were systematically investigated by spectroscopic methods and theoretical calculations to elucidate the effects of introducing different electron-donating groups on their triplet excited state properties. All three complexes possess aggregation-induced phosphorescence emission (AIPE) behaviors. Critically, the relationship between the size of organic ligands and AIPE behaviors for these complexes has been characterized. Their significant AIPE properties predicted that they could be used as efficient latent fingerprint (LFP) developers. Rapid (within 10 s) incubation in Ir(III) complex solution produced high-resolution, naked-eye visible and mobile-photographable LFP images, which could provide fast, reproducible and identifiable analyses of level 3 details for LFPs accurately. In addition, complex Ir-PhCz shows the best imaging of the LFP due to its green light emission and high quantum yield (24.5 %) in solid state. This rapid and practical LFP visualization methodology based on AIPE developers could provide a reliable solution for LFPs detection and investigations in actual scenarios.

A Physical Organic Chemistry Approach to Developing Cyclopropenium-Based Energy Storage Materials for Redox Flow Batteries

ConspectusRedox flow batteries (RFBs) represent a promising modality for electrical energy storage. In these systems, energy is stored via paired redox reactions of molecules on opposite sides of an electrochemical cell. Thus, a central objective for the field is to design molecules with the optimal combination of properties to serve as energy storage materials in RFBs. The ideal molecules should undergo reversible redox reactions at relatively high potentials (for the molecule that is oxidized during battery charging, called the catholyte) or low potentials (for the species that is reduced during battery charging, called the anolyte). Furthermore, anolytes and catholytes must be highly soluble in the electrolyte solution and stable to extended electrochemical cycling in all battery-relevant redox states. The ideal candidates would undergo more than one reversible electron transfer event. Finally, the optimal structures should be resistant to crossover through a selective separator in order to maintain isolation of the two sides of the cell. This Account describes our design and optimization of organic molecules for this application. We first provide background for the metrics and experiments used to characterize anolytes/catholytes and to progress them toward deployment in flow batteries. We then use our studies of aminocyclopropenium-based catholytes to illustrate this workflow and approach.We identified tris(dimethylamino) cyclopropenium hexafluorophosphate as a first-generation catholyte for nonaqueous RFBs based on literature reports from the 1970s describing its reversible chemical and electrochemical oxidation. Cyclic voltammetry and electrochemical cycling experiments in acetonitrile/LiPF6 confirmed that this molecule undergoes oxidation at relatively high potential (0.86 V versus ferrocene/ferrocenium) and exhibits moderate stability toward charge-discharge cycling. Replacing the methyl groups with isopropyl substituents led to enhanced cycling stability but poor solubility of the radical dication (<0.1 M in acetonitrile). Solubility was optimized using quantitative structure-property relationship modeling, which predicted derivatives with ≥10-fold enhanced solubility. Cyclopropeniums with 300-500 mV higher redox potentials were identified by replacing one of the dialkylamino substituents with a less electron-donating thioalkyl or aryl group. Multielectron catholytes were developed by creating hybrid structures that contain a di(amino) cyclopropenium conjugated with a phenothiazine moeity. Finally, oligomeric tris(amino) cyclopropeniums were designed as crossover resistant catholytes. Optimization of their solubility enabled the deployment of these oligomers in high concentration asymmetric redox flow batteries with energy densities that are comparable to the state-of-the-art commercial aqueous inorganic systems.

Diastereoselective and Enantioselective Synthesis of α-p-Methoxyphenoxy-β-Lactones: Dependence on the Stereoelectronic Properties of the β-Hydroxy-α-p-Methoxyphenoxycarboxylic Acid Precursors.

Treatment of β-hydroxy-α-p-methoxyphenoxy carboxylic acids derived from the asymmetric glycolate aldol addition reaction with p-nitrobenzenesulfonyl chloride yielded divergent results depending on the nature of the β-substituent of the carboxylic acid. Substrates bearing either alkyl substituents (R = -n-butyl, -n-octyl, -benzyl, isopropyl, -tert-butyl) or aryl systems bearing electron-withdrawing substituents (R = -p-C6H4Cl, -p-C6H4Br, -p-C6H4NO2) yielded β-lactones. In contrast, α-p-methoxyphenoxy-β-hydroxycarboxylic acids bearing electron-donating aryl groups or the sterically demanding 2-naphthyl group formed (Z)-alkenes.

Quantitative Structure-Property Relationship Modelling for the Prediction of Singlet Oxygen Generation by Heavy-Atom-Free BODIPY Photosensitizers*.

Heavy‐atom‐free sensitizers forming long‐living triplet excited states via the spin‐orbit charge transfer intersystem crossing (SOCT‐ISC) process have recently attracted attention due to their potential to replace costly transition metal complexes in photonic applications. The efficiency of SOCT‐ISC in BODIPY donor‐acceptor dyads, so far the most thoroughly investigated class of such sensitizers, can be finely tuned by structural modification. However, predicting the triplet state yields and reactive oxygen species (ROS) generation quantum yields for such compounds in a particular solvent is still very challenging due to a lack of established quantitative structure‐property relationship (QSPR) models. In this work, the available data on singlet oxygen generation quantum yields (ΦΔ) for a dataset containing >70 heavy‐atom‐free BODIPY in three different solvents (toluene, acetonitrile, and tetrahydrofuran) were analyzed. In order to build reliable QSPR model, a series of new BODIPYs were synthesized that bear different electron donating aryl groups in the meso position, their optical and structural properties were studied along with the solvent dependence of singlet oxygen generation, which confirmed the formation of triplet states via the SOCT‐ISC mechanism. For the combined dataset of BODIPY structures, a total of more than 5000 quantum‐chemical descriptors was calculated including quantum‐chemical descriptors using density functional theory (DFT), namely M06‐2X functional. QSPR models predicting ΦΔ values were developed using multiple linear regression (MLR), which perform significantly better than other machine learning methods and show sufficient statistical parameters (R=0.88–0.91 and q2=0.62–0.69) for all three solvents. A small root mean squared error of 8.2 % was obtained for ΦΔ values predicted using MLR model in toluene. As a result, we proved that QSPR and machine learning techniques can be useful for predicting ΦΔ values in different media and virtual screening of new heavy‐atom‐free BODIPYs with improved photosensitizing ability.

Redox-active tetraaryldibenzoquinodimethanes.

Quinodimethanes (QDs) are a class of non-aromatic π-conjugated compounds that are well-known to be interconvertible scaffolds in many response systems. While parent ortho- and para-QDs (o-QD and p-QD) can be easily converted to benzocyclobutenes or oligomers/polymers by the formation of C-C bonds at α-positions, the attachment of four phenyl groups to these reactive sites makes o-Ph4QD and p-Ph4QD long-lived. We have demonstrated that further dibenzo-annulation of such tetraaryl QD units also drastically increases their stability, and many tetraarylated dibenzoquinodimethane derivatives have been developed. This Feature Article shows our milestones in creating functional redox systems, where drastic changes in structure occur upon electron transfer (dynamic redox "dyrex" behaviour).

Modulating the Properties of Azulene-containing Polymers Through Functionalization at the 2-Position of Azulene.

Poly(2-arylazulene-alt-fluorene) and poly(2-arylazulene-alt-thiophene) are synthesized via Suzuki and Stille cross-coupling polymerization, respectively, using 1,3-dibromo-2-arylazulenes as monomers, which are prepared by a novel directed C-H activation method of 2-carboxylic azulene and subsequent bromination reaction. Our study shows that functionalization at the 2-position of azulene monomers influences polymer properties. For instance, different from electron-withdrawing groups that discourage the protonation of azulene, electron-donating aryl groups, however, enhances the sensitivity of response to acid. Protonation of the polymers leads to significant shifts in absorption spectra accompanying with obvious color changes from green to brown in majority cases because of the formation of poly(azulenium cation). The electrochromic properties of polymers are examined, exhibiting that nature of aryl group at the 2-position of azulene influences the stability of their electrochromic devices.

Electronic and Steric Effects on the Reductive Elimination of Anionic Arylferrate(III) Complexes

Arylferrate(III) complexes Ph3 FeR- (R=para- and ortho-substituted aryl) are proposed as model systems for the in-depth investigation of reductive eliminations from organoiron(III) species. Electrospray ionization transfers the arylferrate complexes prepared in situ from solution into the gas phase, where mass selection ensures a well-defined population of reactant ions. Upon gas-phase fragmentation, the arylferrate complexes undergo reductive elimination of the cross-coupling product PhR as well as the homo-coupling product Ph2 . The measured branching ratios between the two competing reaction channels are used to construct a Hammett plot, which shows that electron-donating aryl groups R favor the formation of the cross-coupling product. In this way, the complexes avoid the build-up of too much electron density at the iron center during the reductive elimination. ortho Substitution in R increases the fraction of the homo-coupling product, presumably by hindering the approach between the two aryl groups participating in the reductive elimination. The obtained mechanistic insight substantially advances our understanding of one of the central elementary steps of transition-metal-catalyzed cross-coupling reactions.

Accessing the Triplet State in Heavy‐Atom‐Free Perylene Diimides

Previous studies of perylenediimides (PDIs) mostly utilized the lowest singlet excited state S1 . Generation of a triplet excited state (T1 ) in PDIs is important for applications ranging from photodynamic therapy to photovoltaics; however, it remains a formidable task. Herein, we developed a heavy-atom-free strategy to prompt the T1 ←S1 intersystem crossing (ISC) by introducing electron-donating aryl (Ar) groups at the head positions of an electron-deficient perylenediimide (PDI) core. We found that the ISC efficiency increases from 8 to 54 % and then to 86 % by increasing the electron-donating ability of head-substituted aryl groups from phenyl (p-PDI) to methoxyphenyl (MeO-PDI) and then to methylthioxyphenyl (MeS-PDI). By enhancing the intramolecular charge-transfer (ICT) interaction from p-PDI to MeO-PDI, and then to MeS-PDI, singlet oxygen generation via energy-transfer reactions from T1 of PDIs to (3)O2 was demonstrated with the highest yield of up to 80 %. These results provide guidelines for developing new triplet-generating PDIs and related rylene diimides for optoelectronic applications.

Phthalimide Compounds Containing a Trifluoromethylphenyl Group and Electron-Donating Aryl Groups: Color-Tuning and Enhancement of Triboluminescence.

Trifluoromethylphenyl-substituted phthalimide derivatives favorably form triboluminescence (TL) active noncentrosymmetric crystals. Oligothienyl-, oligophenyl-, and naphthyl-substituted phthalimide derivatives were successfully developed as a series of metal free TL compounds. X-ray crystal structure analyses of bithienyl and naphthyl derivatives revealed noncentrosymmetric layer structures in the same direction. Introduction of suitable electron rich π-units such as thienyl groups enhances their photoluminescence and TL characteristics, and the colors can be also controlled in the visible region. A rigid naphthyl-substituted imide derivative exhibits extremely high TL performance.

Alkylation of 5-substituted NH-tetrazoles by alcohols in the superacid CF3SO3H

Reactions of 5-substituted NH-tetrazoles with alcohols in the superacid CF3SO3H have been studied. Both the structure of the tetrazole and the nature of alcohol were found to dramatically influence the selectivity of the reaction and yields of products. Tetrazoles bearing phenyl, electron-donating aryl, or benzyl groups at the 5-position, have been alkylated using various alcohols (including MeOH and EtOH) in CF3SO3H upon heating at 60°C for 0.3–12h to afford 2-alkyl-2H-tetrazoles in 30–98% yields.

Comparison of electronic effects of β-aryl substituents on optical and electrochemical properties of 5,15-diazaporphyrin π-systems

The syntheses and optical/electrochemical properties of 3-aryl-10,20-dimesityl-5,15-diazaporphyrin-metal complexes (MDAPs; mesityl = 2,4,6-trimethylphenyl; M = Ni , Zn ) are reported. Treatment of 3-bromo-MDAPs with arylboronic acids in the presence of a Pd catalyst and a bulky phosphine ligand in a dioxane-water mixed solvent afforded the corresponding 3-aryl-MDAPs in moderate to good yields. X-ray crystallographic analysis of p- EtO 2 CC 6 H 4- NiDAP showed that the β-aryl group was tilted toward the NiDAP ring, with a dihedral angle of 21.7°. In the UV-visible absorption spectra, all the Ar-MDAPs showed intense Q-bands attributable to HOMO-to-LUMO transitions. The para substituents were found to influence the HOMO energies, which eventually resulted in fine tuning of the HOMO–LUMO gaps of the diazaporphyrin chromophores. It is worth noting that the p- Ph 2 NC 6 H 4- ZnDAP showed broad absorption and emission bands in the visible-near-infrared regions. The large Stokes shifts and their linear solvation energy relationships vs. orientation polarizability show that this Ph 2 N -substituted derivative has intrinsically high charge transfer from the triphenylamine (donor) to the ZnDAP (acceptor) unit. These experimental observations were supported by theoretical calculations for model Ar-ZnDAP compounds. These results confirm that the introduction of a highly electron-donating aryl group at the peripheral β-carbon is a promising strategy for enhancing the light-harvesting and light-emitting abilities of diazaporphyrin-based π-systems in the visible-near-infrared regions.

Environment-sensitive fluorescent probe: a benzophosphole oxide with an electron-donating substituent.

Electron-donating aryl groups were attached to electron-accepting benzophosphole skeletons. Among several derivatives thus prepared, one benzophosphole oxide was particularly interesting, as it retained high fluorescence quantum yields even in polar and protic solvents. This phosphole-based compound exhibited a drastic color change of its fluorescence spectrum as a function of the solvent polarity, while the absorption spectra remained virtually unchanged. Capitalizing on these features, this phosphole-based compound was used to stain adipocytes, in which the polarity of subcellular compartments could then be discriminated on the basis of the color change of the fluorescence emission.

Asymmetrical squaraines for high-performance small-molecule organic solar cells with a short circuit current of over 12 mA cm(-2).

An asymmetrical squaraine dye (Py-3) with its two electron-donating aryl groups directly linked to the electron-withdrawing squaric acid core possesses an ideal bandgap of 1.33 eV, together with an intense and broad absorption band in the range 550-950 nm. Hence, the resulting solution-processed solar cells display an impressive Jsc of 12.03 mA cm(-2) and a PCE of 4.35%.

Synthesis, characterization and electronic effects investigations of new 5,7-disubstituted tris(8-quinolinolate)Al(III) complexes

Eight 5,7-diaryl-8-hydroxyquinoline ligands were synthesized and characterized by 1H, 13C NMR spectroscopy and mass spectrometry. The electron-donating and electron-withdrawing aryl groups were attached to the 5- and 7-positions of the quinolinolate ring via Suzuki coupling reaction. The aluminum complexes of these ligands exhibited successful tuning in the emission color, covering a large segment of the visible spectrum.

Aroylspirophosphoranes bearing two naphth-1,8-diyl-8-oxy groups: synthesis, crystal structure, and np(Oapical)→π∗(C[dbnd]O) charge transfer interaction

The reactions of aroyl chlorides with the lithium phosphoranide generated from bis(naphth-1,8-diyl-8-oxy)phosphorane 1 afforded aroylspirophosphoranes 3a–f. The p-anisoyl- and p-tert-butylbenzoylphosphoranes 3a and 3b bearing an electron-donating aryl group were stable to moisture on silica gel. The crystal structures of p-anisoyl-, p-tert-butylbenzoyl-, benzoyl-, and p-fluorobenzoylphosphorane (3a, 3b, 3d, and 3e) elucidated by X-ray structural analysis suggested effective intramolecular np(Oapical)→π∗(CO) charge transfer stabilization to be operative.

ChemInform Abstract: Suzuki—Miyaura Reactions of 2,7‐Dichloro‐1,8‐naphthyridine.

AbstractNovel 2,7‐diaryl‐ and 2,7‐dialkenyl derivatives are prepared under optimized conditions.

Synthesis, Electrochemistry, and Photophysics of a Family of Phlorin Macrocycles That Display Cooperative Fluoride Binding

A homologous set of 5,5-dimethylphlorin macrocycles in which the identity of one aryl ring is systematically varied has been prepared. These derivatives contain ancillary pentafluorophenyl (3H(Phl(F))), mesityl (3H(Phl(Mes))), 2,6-bismethoxyphenyl (3H(Phl(OMe))), 4-nitrophenyl (3H(Phl(NO2))), or 4-tert-butylcarboxyphenyl (3H(Phl(CO2tBu))) groups at the 15-meso-position. These porphyrinoids were prepared in good yields (35-50%) and display unusual multielectron redox and photochemical properties. Each phlorin can be oxidized up to three times at modest potentials and can be reduced twice. The electron-donating and electron-releasing properties of the ancillary aryl substituent attenuate the potentials of these redox events; phlorins containing electron-donating aryl groups are easier to oxidize and harder to reduce, while the opposite trend is observed for phlorins containing electron-withdrawing functionalities. Phlorin substitution also has a pronounced effect on the observed photophysics, as introduction of electron-releasing aryl groups on the periphery of the macrocycle is manifest in larger emission quantum yields and longer fluorescence lifetimes. Each phlorin displays an intriguing supramolecular chemistry and can bind 2 equiv of fluoride. This binding is allosteric in nature, and the strength of halide binding correlates with the ability of the phlorin to stabilize the buildup of charge. Moreover, fluoride binding to generate complexes of the form 3H(Phl(R))·2F(-) modulates the redox potentials of the parent phlorin. As such, titration of phlorin with a source of fluoride represents a facile method to tune the ability of this class of porphyrinoid to absorb light and engage in redox chemistry.

Suzuki-Miyaura Reactions of 2,7-Dichloro-1,8-naphthyridine

2,7-Diaryl- and 2,7-dialkenyl-1,8-naphthyridines were prepared in high yields by Suzuki–Miyaura reactions of 2,7-dichloro-1,8-naphthyridines. While most of the products proved to be not or only weakly fluorescent, we observed a strong fluorescence in case of 2,7-bis(4-methoxyphenyl)-1,8-naphthyridine containing two electron-donating aryl groups.

Multicomponent domino reactions of acetylenedicarboxylates: divergent synthesis of multi-functionalized pyrazolones and C-tethered bispyrazol-5-ols

An efficient and practical methodology of selectively divergent synthesis of arylidene pyrazolones and C-tethered bispyrazol-5-ols via multicomponent domino reactions of acetylenedicarboxylates, phenylhydrazine and aromatic aldehydes has been developed. The electron-donating aryl groups (EDAG)-attached aldehydes resulted in the pyrazolone skeleton, whereas the electron-withdrawing aryl groups (EWAG) led to the C-tethered bispyrazol-5-ols with simultaneous formation of two new pyrazole rings.