Outer Phenyl Rings Research Articles

Engineering Blue Fluorescent Bulk Emitters for OLEDs: Triplet Harvesting by Green Phosphors

Triplet harvesting in organic light-emitting diodes (OLEDs) from a blue fluorescent to a green phosphorescent emitter is important for the development of highly efficient white OLEDs for lighting applications. Here, we report new blue fluorescent bulk emitters with high triplet energies for triplet harvesting in OLEDs. Based on the chemical structure of the highly efficient blue emitter N,N′-di-1-naphthalenyl-N,N′-diphenyl-[1,1′:4′,1″:4″,1‴-quaterphenyl]-4,4‴ diamine (4P-NPD), two new quarterphenylene compounds are designed and synthesized. Their experimentally obtained ionization potentials, singlet, and triplet levels are compared to quantum chemical calculations. We show that the incorporation of repulsive methyl groups leads to a twist of the outer phenyl rings of the molecule and increases the triplet level. Finally, triplet harvesting OLEDs comprising these two new compounds as bulk emitters are electrically and optically characterized. We demonstrate that both materials allow triplet harvesting by ...

Experimental and Theoretical Study of the n‐Doped Successive Polyanions of Oligocruciform Molecular Wires: Up to Five Units of Charge

The electronic structure of polyanions of sterically encumbered triisopropylsilyl-substituted linear and cyclic oligo(phenyleneethynylene)s (Monomer, Trimer, Pentamer, and Triangle) is investigated by electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and UV/Vis-near-infrared (NIR) spectroscopies, cyclic voltammetry, and theoretical calculations (DFT). Increasing anion orders are generated sequentially in vacuo at room temperature by chemical reaction with potassium metal up to the pentaanion. The relevance of these compounds acting as electron reservoirs is thus demonstrated. Even-order anions are EPR silent, whereas the odd species exhibit different signatures, which are identified after comparison of the measured hyperfine couplings by ENDOR spectroscopy with those predicted by DFT calculations. With increasing size of the oligomers the electron spin density is first distributed over the backbone carbon atoms for the monoanions, and then further localized at the outer phenyl rings for the trianion species. Examination of the UV/Vis-NIR spectra indicates that the monoanions (T(.-) , P(.-) ) exhibit two transitions in the Vis-NIR region, whereas a strong absorption in the IR region is solely observed for higher reduced states. Electronic transitions of the neutral monoanions and trianions are redshifted with increasing oligomer size, whereas for a given oligomer a blueshift is observed upon increasing the charge, which suggests a localization of the spin density.

Steric hindrance in cationic and neutral rhodamine 6 G molecules adsorbed on Au nanoparticles

The adsorption of cationic and neutral R6G molecules on Au nanoparticles was elucidated by surface enhanced Raman scattering (SERS). The steric hindrance at hydroethyl amino (‐N(H)Et) groups in R6G was evidenced by the observation that R6G+ adsorb on as‐prepared gold nanoparticles (AuNPs) only with electrostatic forces, in contrast to the electrostatic and chemical adsorption of R123+ with dihydro amino (‐NH2) groups on as‐prepared AuNPs. Large steric hindrance at the amino groups in R6G yielded saturated coverage of 700 molecules/AuNP for R6G+ significantly fewer than 1000 molecules/AuNP for R123+. In addition, neutral R6G0 on AuNPs showed markedly enhanced peaks at 1200–1600 cm−1, which were not observed in Raman spectra of R6G0 in bulk solution, and also in SERS of R6G+ on AuNPs. These bands are attributed to vibrational modes of an outer phenyl ring and ethyl amino groups, which are vertical to a xanthene plane, on the basis of theoretical analysis of molecular vibrations. Thus, Raman scattering of these bands is enhanced under an inclined orientation of R6G0 molecules chemisorbed on AuNPs via lone pair electrons at amino groups. Copyright © 2013 John Wiley & Sons, Ltd.

Antitubercular nitrofuran isoxazolines with improved pharmacokinetic properties

A series of tetracyclic nitrofuran isoxazoline anti-tuberculosis agents was designed and synthesized to improve the pharmacokinetic properties of an initial lead compound, which had potent anti-tuberculosis activity but suffered from poor solubility, high protein binding and rapid metabolism. In this study, structural modifications were carried on the outer phenyl and piperidine rings to introduce solubilizing and metabolically blocking functional groups. The compounds generated were evaluated for their in vitro antitubercular activity, bacterial spectrum of activity, solubility, permeability, microsomal stability and protein binding. Pharmacokinetic profiles for the most promising candidates were then determined. Compounds with phenyl morpholine and pyridyl morpholine outer rings were found to be the most potent anti-tuberculosis agents in the series. These compounds retained a narrow antibacterial spectrum of activity, with weak anti-Gram positive and no Gram negative activity, as well as good activity against non-replicating Mycobacterium tuberculosis in a low oxygen model. Overall, the addition of solubilizing and metabolically blocked outer rings did improve solubility and decrease protein binding as designed. However, the metabolic stability for compounds in this series was generally lower than desired. The best three compounds selected for in vivo pharmacokinetic testing all showed high oral bioavailability, with one notable compound showing a significantly longer half-life and good tolerability supporting its further advancement.

Phenylnaphthalenes: Sublimation Equilibrium, Conjugation, and Aromatic Interactions

In this work, the interplay between structure and energetics in some representative phenylnaphthalenes is discussed from an experimental and theoretical perspective. For the compounds studied, the standard molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, were determined by the measurement of the vapor pressures as a function of T, using a Knudsen/quartz crystal effusion apparatus. The standard molar enthalpies of formation in the crystalline state were determined by static bomb combustion calorimetry. From these results, the standard molar enthalpies of formation in the gaseous phase were derived and, altogether with computational chemistry at the B3LYP/6-311++G(d,p) and MP2/cc-pVDZ levels of theory, used to deduce the relative molecular stabilities in various phenylnaphthalenes. X-ray crystallographic structures were obtained for some selected compounds in order to provide structural insights, and relate them to energetics. The thermodynamic quantities for sublimation suggest that molecular symmetry and torsional freedom are major factors affecting entropic differentiation in these molecules, and that cohesive forces are significantly influenced by molecular surface area. The global results obtained support the lack of significant conjugation between aromatic moieties in the α position of naphthalene but indicate the existence of significant electron delocalization when the aromatic groups are in the β position. Evidence for the existence of a quasi T-shaped intramolecular aromatic interaction between the two outer phenyl rings in 1,8-di([1,1'-biphenyl]-4-yl)naphthalene was found, and the enthalpy of this interaction quantified on pure experimental grounds as -(11.9 ± 4.8) kJ·mol(-1), in excellent agreement with the literature CCSD(T) theoretical results for the benzene dimer.

Laterally substituted symmetric and nonsymmetric salicylideneimine-based bent-core mesogens

Bent-core mesogens have gained considerable importance due to their ability to form new mesophases with unusual properties. Relationships between the chemical structure of bent-core molecules and the type and physical properties of the formed mesophases are relatively unknown in detail and differ strongly from those known for calamitic liquid crystals. In this paper symmetric and nonsymmetric five-ring salicylideneaniline-based bent-core mesogens are presented, and the effect of lateral substituents attached at the outer phenyl rings (F, Cl, Br) or the central phenyl ring (CH3) on the liquid-crystalline behaviour and on the physical properties is studied. Corresponding benzylideneaniline-based compounds were additionally prepared in order to study the influence of the intramolecular hydrogen bond. The occurring mesophases were investigated by differential scanning calorimetry, polarising microscopy, X-ray diffraction and dielectric and electro-optical measurements. The paper reports on new findings with respect to the structure–property relationships of bent-core mesogens. On one hand, the disruptive effect of laterally substituted halogen atoms, F, Cl and Br, on the mesophase behaviour of three isomeric series was much lower than expected. On the other hand, an increase of the clearing temperature by 34 K was observed, caused by small lateral substituents. The electro-optical behaviour, especially the type of polar switching and corresponding molecular movements, is sensitive to variations in the molecular structure.

2-Bromo-p-terphenyl

In the title compound, C18H13Br, the dihedral angles between the mean planes of the central benzene ring and the mean planes of the outer phenyl and bromo­phenyl rings are 33.47 (8) and 66.35 (8)°, respectively. In the crystal, weak C—H⋯π and inter­molecular Br⋯Br [3.5503 (15) Å] inter­actions contribute to the stabilization of the packing.

The effect of substitution on reorganization energy and charge mobility in metal free phthalocyanine

To gain insight into how the electronic properties of discotic organic materials may be modified through substitution, the reorganization energy and the charge mobility of metal free phthalocyanine, and of several mono-substituted derivatives, are studied by electronic structure methods. It is found that the reorganization energy of phthalocyanine is not significantly changed by substitution on an outer phenyl ring, but is more strongly influenced when the inner crown amine ring is substituted. The relationship between reorganization energy and substituent is studied through the use of; substituent constant, HOMO energy, and geometry relaxation. The computed charge mobility shows stronger relationship to coupling matrix element than reorganization energy. A hybrid computational screening method in which the reorganization energy is calculated at the DFT level and the coupling matrix element is calculated at the AM1 level shows good predicting power for trends in charge mobility at reduced computational expense.

Thermodynamic study of 1,2,3-triphenylbenzene and 1,3,5-triphenylbenzene

The energetic study of 1,2,3-triphenylbenzene (1,2,3-TPhB) and 1,3,5-triphenylbenzene (1,3,5-TPhB) isomers was carried out by making use of the mini-bomb combustion calorimetry and Knudsen mass-loss effusion techniques. The mini-bomb combustion calorimetry technique was used to derive the standard ( p° = 0.1 MPa) molar enthalpies of formation in the crystalline state from the measured standard molar energies of combustion for both isomers. The Knudsen mass-loss effusion technique was used to measure the dependence with the temperature of the vapour pressure of crystalline 1,2,3-TPhB, which allowed the derivation of the standard molar enthalpy of sublimation, by application of the Clausius–Clapeyron equation. The sublimation study of 1,3,5-TPhB had been performed previously. From the combination of data obtained by both techniques, the standard molar enthalpies of formation in the gaseous state, for both isomers, at T = 298.15 K, were calculated. The results indicate a higher stability of the 1,3,5-TPhB isomer relative to 1,2,3-TPhB, similarly to the terphenyls. Nevertheless, the 1,2,3-TPhB isomer is not as energetically destabilized as one might expect, supporting the existence of a π–π displacive stacking interaction between both pairs of outer phenyl rings. The volatility difference between the two isomers is ruled by the enthalpy of sublimation. The volatility of the 1,2,3-TPhB is two orders of magnitude higher than the 1,3,5-TPhB isomer, at T = 298.15 K. Δ c U m ∘ / ( kJ · mol - 1 ) Δ f H m ∘ ( g ) / ( kJ · mol - 1 ) 1,2,3-Triphenylbenzene (1,2,3-TPhB) −12248.2 ± 4.1 376.7 ± 5.3 1,3,5-Triphenylbenzene (1,3,5-TPhB) −12224.6 ± 3.6 366.8 ± 4.9

Supramolecular Ring Banded Prototype Liquid Crystalline Oligo(phenylenevinylene)

We report a new ring banded supramolecular structure in thermotropic liquid crystalline oligo(phenylenevinylene) (OPV) via a melt crystallization process. A series of structurally different OPV molecules were synthesized using tricyclodecanemethanol (TCD) as a bulky pendant unit to trace ring banded morphology. Among all, an OPV molecule with rigid bis-TCD units in the central core and flexible dodecyl chains at the outer phenyl rings (BTCD-BDD-OPV) was found to show ring banded morphologies, which is a first of its kind in pi-conjugated materials. BTCD-BDD-OPV experiences strong aromatic pi-pi interactions in both film and liquid crystalline (LC) frozen stage. The pi-induced aggregation leads to lamellar self-assembly of OPV-mesogens that subsequently undergo helical crystal growth, thereby producing dark and bright ring banded patterns. Variable temperature X-ray diffraction analysis revealed the existence of three peaks at 27.07, 13.97, and 8.90 A corresponding to 001, 002, and 003 fundamental layers, respectively, thus confirming the lamellar self-assembly of OPV-mesogens. Electron microscopic (SEM and TEM) analysis of the LC frozen sample showed images confirming helical microcrystalline assembly and providing direct evidence for the self-organization mechanism. Detailed photophysical experiments such as excitation, emission, and time-resolved fluorescence decay studies indicated that BTCD-BDD-OPV has very strong pi-pi interaction in both film and LC frozen stage, which was found to be main driving force for the formation of supra-ring structure. Upon illumination with light, the OPV chromophores in the LC phase were excited and the color of the samples turned into luminescent green ring bands.

Reversible photoisomerization of an azobenzene-functionalized self-assembled monolayer probed by sum-frequency generation vibrational spectroscopy

Sum-frequency generation (SFG) vibrational spectroscopy is employed to investigate the reversible, photoinduced trans/cis isomerization of an azobenzene-functionalized self-assembled monolayer (SAM) on a gold substrate. A C[triple bond]N marker group at the outer phenyl ring is used as a direct measure of the switching state. The azobenzene unit is connected to the surface by a tripodal linker system with an adamantane core, which results in both a sufficient decoupling of the functional azobenzene unit from the metallic substrate and a free volume to prevent steric hindrance, thus allowing the isomerization process. Optical excitation at 405 nm induces the trans-->cis isomerization, whereas light exposure at 470 nm leads to the back reaction. The effective cross sections for the reactions are sigma(eff)(cis) = 4 +/- 1 x 10(-18) cm(2) at 405 nm (trans-->cis) and sigma(eff)(trans) = 2.5 +/- 0.9 x 10(-19) cm(2) at 470 nm (cis-->trans). We propose that the photoisomerization is driven by a direct (intramolecular) electronic excitation of the azobenzene conjugate, analogous to the free molecules in solution.

5-Amino-1-(5-methyl-1-phenylpyrazol-4-ylcarbonyl)pyrazole-4-carbonitrile

In the mol­ecule of the title compound, C15H12N6O, the central pyrazole ring forms dihedral angles of 25.10 (7) and 40.22 (7)° with the outer pyrazole and phenyl rings, respectively. In the crystal structure, centrosymmetrically related mol­ecules are linked into dimers by inter­molecular N—H⋯N hydrogen bonds. The dimers inter­act along the b axis through inter­molecular C—H⋯O hydrogen bonds to form chains. There is an intramolecular N—H⋯O hydrogen bond.

N,N′-(4,5-Dichloro-o-phenylene)dibenzamide

In the title mol­ecule, C20H14Cl2N2O2, the dihedral angles between the central benzene ring and the two outer phenyl rings are 58.92 (7) and 21.91 (9)°. While an intra­molecluar N—H⋯O hydrogen bond may influence the mol­ecular conformation, an inter­molecular N—H⋯O hydrogen bond connects mol­ecules into centrosymetric dimers.

N,N′-Bis[(2-phenyl-2H-1,2,3-triazol-4-yl)methylidene]benzene-1,4-diamine

The centrosymmetric title compound, C24H18N8, was prepared by reaction of 2-phenyl-1,2,3-triazole-4-carbaldehyde with 1,4-phenyl­ene­di­amine. The dihedral angle between the outer phenyl ring and the triazole ring is 6.9 (3)°. The crystal structure is stabilized by inter­molecular aromatic π–π inter­actions between the parallel triazole and benzene rings [the centroid–centroid separation is 3.485 (2) A].

Octopolar Chromophores Based on Donor- and Acceptor-Substituted 1,3,5-Tris(phenylethynyl)benzenes: Impact of meta-Conjugation on the Molecular and Electronic Structure by Means of Spectroscopy and Theory

The molecular and electronic structures of a series of all-meta-substituted phenylacetylene mesitylenes peripherally substituted with donor or acceptor (D-A) groups are studied. The impact of meta- and para-substitution patterns is also analyzed by employing Raman and optical spectroscopies in conjunction with theoretical calculations. Outer phenyl rings display a partial quinoid character induced by two different motifs: (i) outer phenyls --> triple bond charge transfer for the cases where these phenyls are substituted with electron-donors; (ii) double electron withdrawing effect in the molecules with the peripheral phenyls substituted with electron acceptors. A moderate tuning of the optical gap is observed in agreement with the partial blockade of pi-electron conjugation exerted by the meta disposition. The orbital structure of the compounds partially preserves that of the mesitylene group showing extra-conjugation due to the addition of the arms, so that conjugation is not entirely obstructed but partially impeded in the ground electronic state (i.e., electron occupied orbitals). As for the excited states, the low-lying energy empty orbitals offer better conditions for full conjugation over the whole molecular scaffold. Interesting optical properties such as overlapping centers along the lowest energy optical excitations and enhanced optical transparency with importance for the application of these materials in optoelectronics have been justified on the basis of the electronic structure. A greater degree of quinoidization, and more allowed pi-electron delocalization, over the entire molecule is recognized in the case of linear phenylacetylenes substituting in para positions the central core.

1-D arrays of Cu(I)-Schiff base maintained by fourfold phenyl embraces isolating diiodocuprate(I) anions

The reaction of CuI with the bidentate Schiff base ligand (Phca 2-dab) in acetonitrile yields a new mononuclear Cu(I) complex [Cu(Phca 2-dab) 2][CuI 2]. The structure contains cationic moieties of Cu I ion coordinated to four N atoms of two Phca 2-dab ligands in a distorted tetrahedral fashion and isolated linear diiodocuprate(I) anions. The Phca 2-dab ligand adopts a Z, Z configuration. A supramolecular motif that is a one-dimensional array of Phca 2-dab embraces formed by the complex has been identified from the crystal packing analysis. The Phca 2-dab embrace involves two complexes attracted by two edge-to-face (ef) interactions by the outer phenyl rings of the ligands.

2-(Biphenyl-2-yl)-5-(1-methylhydrazino)-1,3,4-thiadiazole: a thiadiazole–hydrazine derivative with anticonvulsant properties

In the title compound, C15H14N4S, the outer phenyl ring makes an angle of 101.4 (2)° with the plane through the inner benzene ring, and the planes of the thia­diazole ring and the attached benzene ring inter­sect at an angle of 146.7 (2)°. In addition to weak N—H⋯N hydrogen bonds, creating a two-dimensional network parallel to the bc plane of the crystal structure, there is also one non-standard hydrogen-bond inter­action of the type C—H⋯N. Stereochemical comparison with the closely related compound 1-[5-(biphenyl-2-yl)-1,3,4-thia­diazol-2-yl]methanaminium chloride shows that the two compounds utilize the same mechanism for anticonvulsant activity.

Stereochemical basis for activity in thiadiazole anticonvulsants: 1-[5-(biphenyl-2-yl)-1,3,4-thiadiazol-2-yl]methanaminium chloride and two inactive analogues, 2-(biphenyl-4-yl)-5-[2-(1-methylethylidene)hydrazino]-1,3,4-thiadiazole and the methanol solvate of its hydrochloride salt

In 1-[5-(biphenyl-2-yl)-1,3,4-thiadiazol-2-yl]methanaminium chloride, C15H14N3S+.Cl-, the protonation occurs at the amine N atom. The outer phenyl ring makes an angle of 88.0 (2) degrees with the plane through the inner benzene ring, and the planes of the thiadiazole ring and the attached benzene ring intersect at an angle of 165.5 (4) degrees . In addition to classical N-H...N and N-H...Cl(-) hydrogen bonds producing chains parallel to the c axis, there are weak C-H...N and C-H...Cl- hydrogen bonds. The hydrogen bonds and packing interactions result in hydrophilic and hydrophobic planar areas in the crystal, perpendicular to the a axis. Stereochemical comparison with phenytoin shows that the two compounds may utilize similar mechanisms of action. 2-(Biphenyl-4-yl)-5-[2-(1-methylethylidene)hydrazino]-1,3,4-thiadiazole, C17H16N4S, where Z' = 2, and the methanol solvate of its hydrochloride salt, 5-(biphenyl-4-yl)-2-[2-(1-methylethylidene)hydrazino]-1,3,4-thiadiazol-3-ium chloride methanol solvate, C17H17N4S+.Cl-.CH3OH, adopt linear almost planar molecular conformations. The para position of the outer phenyl ring in these compounds precludes adoption of the phenytoin anticonvulsant stereochemistry.

The Class II/III Transition Electron Transfer on an Infrared Vibrational Time Scale forN,N‘-Diphenyl-1,4-phenylenediamine Structures

Intramolecular electron transfer (ET) within the class II/III transition for the mixed-valence state of N,N‘-diphenyl-1,4-phenylenediamine (PDA) derivatives which were substituted in the center or the outer phenyl ring and N,N‘-diphenylbenzidine (BZ) was examined. Each compound showed two reversible redox couples. The splitting of the redox waves, ΔE, is related to the interaction intensity between redox sites. The introduction of a substitutent into the central phenylene ring of the PDAs resulted in a decrease in ΔE. A similar result was noted for the expansion of the distance between the redox centers such as in BZ. In opposition, the ΔE of N,N‘-bis(2,6-dimethylphenyl)-1,4-phenylenediamine (2,6-DMPDA) as a compound with substituents introduced into the outer phenyl rings was spread. The mixed-valence state of these compounds also exhibited an intervalence charge transfer (IV-CT) band in the near-IR region which provided the determination of the Marcus reorganization energy (λ), the electron coupling (V)...

Synthesis and characterization of a wholly aromatic rod-like macrocyclic tetraester mesogen from 4,4'-biphenyldicarboxylic acid and catechol

The first example of a wholly aromatic rod-like macrocyclic mesogen has been synthesized by a two step polycondensation of catechol (C) with of 4,4′-biphenyldicarboxylic acid (B). Pure crystalline [2+2] cyclo-dimer was isolated from the polymerization mixture in 25% yield by a single silica gel column chromatogram and it was fully characterized by TLC, GPC, FAB+ MS, FTIR, UV-Vis, 1H NMR, differential scanning calorimetry and polarizing optical microscopy. Structural features and stereochemical aspects of this 28-membered cyclic tetraester were studied by semi-empirical AM1 calculations and Molecular Dynamics simulations. This calamitic macrocyclic mesogen has the two outer coplanar phenyl rings of the C entities linked by two stacked B units forming an extraordinarily rigid and strongly anisometric molecular structure with a long axis of c.20 Å. Whereas its low molecular mass acyclic homologue is far from being mesomorphic, this macrocyclic compound exhibits an enantiotropic nematic mesophase with a clearing temperature higher than that of the high molar mass linear homologue [5.5 × 104 (1.9), M n (M w/M n), GPC].