Influence Of Substituents Research Articles

Various Structural Design Modifications: para-Substituted Diphenylphosphinopyridine Bridged Cu(I) Complexes in Organic Light-Emitting Diodes.

The well-known system of dinuclear Cu(I) complexes bridged by 2-(diphenylphosphino)pyridine (PyrPhos) derivatives Cu2X2L3 and Cu2X2LP2 (L = bridging ligand, P = ancillary ligand) goes along with endless variation options for tunability. In this work, the influence of substituents and modifications on the phosphine moiety of the NP-bridging ligand was investigated. In previous studies, the location of the lowest unoccupied molecular orbital (LUMO) of the copper complexes of the PyrPhos family was found to be located on the NP-bridging ligand and enabled color tuning in the whole visible spectrum. A multitude of dinuclear Cu(I) complexes based on the triple methylated 2-(bis(4-methylphenyl)phosphino)-4-methylpyridine (Cu-1b-H, Cu-1b-MeO, and Cu-1b-F) up to complexes bearing 2-(bis(4-fluorophenyl)phosphino)pyridine (Cu-6a-H) with electron-withdrawing fluorine atoms over many other variations on the NP-bridging ligands were synthesized. Almost all copper complexes were confirmed via single crystal X-ray diffraction analysis. Besides theoretical TDDFT-studies of the electronic properties and photophysical measurements, the majority of the phosphino-modified Cu(I) complexes was tested in solution-processed organic light-emitting diodes (OLEDs) with different heterostructure variations. The best results of the OLED devices were obtained with copper emitter Cu-1b-H in a stack architecture of ITO/PEDOT-PSS (50 nm)/poly-TPD (15 nm)/20 wt % Cu(I) emitter:CBP:TcTA(7:3) (45 nm)/TPBi (30 nm)/LiF(1 nm)/Al (>100 nm) with a high brightness of 5900 Cd/m2 and a good current efficiency of 3.79 Cd/A.

Synthesis, crystal structure, spectroscopic and photophysical studies of novel fluorinated quinazoline derivatives

A novel small library of seven fluorinated quinazoline derivatives was synthesized and for four of them, the crystal structures were solved by single X-ray diffractometer and compared the confirmation of molecules in solution-phase using 2D NOESY experiments. Taking advantage of the series prepared, we were able to describe the influence of various substituents on the core scaffold (fluorinated quinazoline) on its molecular conformations’ intermolecular interactions and on the photoluminescent properties. The Hirshfeld surfaces were used to investigate the structure-directing effects of functional groups in controlling their solid-state behavior. Theoretical DFT calculations were carried out for getting additional knowledge on crystal-state interactions as compared to a gas phase. The photo-physical (UV and fluorescence) properties of all compounds have been studied. among the series, five compounds exhibited excellent photoluminescent properties.

Flavin mimetics: Synthesis and photophysical properties

We report the synthesis of new isoalloxazines using a microwave-assisted approach to make N -substituted-2-nitroanilines followed by one-pot reduction and condensation via Hemmerich’s method. The influence of substituents on positions 7, 8, and 10 of flavin core on the optical properties is investigated. The aliphatic functionalities on N10 give rise to quantum yields of 0.7, while aromatic side-chains quench fluorescence. Relaxed geometries (DFT) of chiral and achiral derivatives have been used for TD-DFT calculations, which yielded good agreement with the experimental UV and CD data.

15N, 13C and 1H NMR study of tautomerism in 2-(phenyldiazenyl-4-substituted naphthalen-1-ols. Influence of substitution in passive components on azo-hydrazo tautomerism

The one- and two-dimensional 15N, 13C and 1H NMR spectra of benzenediazonium chloride coupling product with 4-R-naphthalene-1-ols (R = NO2(1), Br (2), Cl (3), H (4), OCH3(5)) were measured and analysed. It was found that the reaction products exist predominantly in hydrazone forms. Contrary to previously published influence of substituents in diazonium salts, where more electron acceptor types of substituents cause increase contents of hydrazo forms, the situation in compounds 1–5 is completely opposite. Moreover, hydrazone content in 4-nitro-2-[(E)-(4-nitro-phenyl)diazenyl]naphtalen-1-ol (6) combining substitution both in position 4 of passive component and position 4 of active component (i. e. diazonium salt) is higher compared with that in 4-nitro-2-[(E)-(phenyl)diazenyl]naphtalen-1-ol (1).

Influence of N-donor substituents on physicochemical properties of phenanthro[9,10-d]imidazole derivatives

In this study, the synthesis and physicochemical properties (thermal, electrochemical and optical) of three phenanthro[9,10-d]imidazole derivatives with N-donor substituents (PI-1 - PI-3) was presented. All compounds were obtained by condensation reactions with a yield in the range of 61–70%. Their structure was confirmed by NMR spectroscopic methods (1H, 13C, H–H COSY, H–C HMQC and H–C HMBC). The synthesized derivatives were characterized by high thermal stability (above 300 °C). Two of them (PI-1 and PI-3) showed a fully reversible oxidation process, which allowed detailed spectroelectrochemical and electrochemical studies. Absorption and emission properties were tested in four solvents of different polarity. These compounds showed high quantum yields in the range from 18 to 80%. Studies on physicochemical properties have been extended to include detailed theoretical considerations.

Acid-base properties of imidazo[2,1-<i>b</i>] tiazole and tiazolo[3,2-<i> а</i>] benzimidazole derivatives

For over 30 years, azomethine groups have been attracting significant research interest due to their high electrophilicity formed under the influence of strong electrophilic substituents. The combination of a polyhalidealkyl group and functional substitutes in close proximity to the azomethine bond reveals a wide range of possible chemical transformations, one of which is the production of heterocyclic derivatives. Since heterocyclic compounds are of interest in terms of their medical and synthetic prospects, research into the NH-acidity of these compounds is highly relevant. Information on the acid-base properties of such compounds is useful for predicting their reactivity and physical-chemical properties. The potentiometric titration method was used to determine the dissociation constants of the substances under study. As a result, titration curves with a different number of dissociation stages (their number was determined by the number of NH-groups) were obtained, which showed a clear jump in the potential of the indicating electrode. The experimental determination of the acid-base behaviour of the synthesized sulphonylamine-substituted imidazo[2,1-b]tiazoles and thiazolo[3,2-a]benzimidazoles was carried out in dimethylsulphoxide medium. The semi-neutralization potentials were determined using titration curves. A relationship between acidity constants (pK A ) and semi-neutralization potentials was determined. The pK A =f (E 1/2 ) dependence allows the constants of NH-acidity for newly synthesized compounds in dimethylsulphoxide medium to be predicted. The statistical range of the conducted potentiometric titration was determined. The obtained dissociation constants showed a high level of intermediate precision. The variation coefficients ranged from 0.34 to 1.48%. The PASS software was used to calculate the potential of biological activity (Pa) of the compounds under study. The relationship between NH-acidity and biological potential is still ambiguous.

Influence of Substituents in Terephthalate Linker on the Structure of MOFs Obtained from Presynthesized Heterometallic Complex

The synthesis of new porous materials with desired properties is a challenging task. It becomes especially difficult if you need to combine several metals in one framework to obtain a heterometallic node. The use of presynthesized complexes for obtaining of new heterometallic metal–organic frameworks could be essential to solve the problem of tailored synthesis. In our study we use presynthesized heterometallic pivalate complex [Li2Zn2(piv)6(py)2] to obtain new MOFs with heterometallic core as a node of the framework. We are managed to obtain four new heterometallic MOFs: [H2N(CH3)2]2[Li2Zn2(bdc)4]·CH3CN·DMF (1), [Li2Zn2(H2Br2-bdc)(Br2-bdc)3]·2DMF (2), [H2N(CH3)2][LiZn2(ndc)3]·CH3CN (3) and [{Li2Zn2(dmf)(py)2}{LiZn(dmf)2}2 (NO2-bdc)6]·5DMF (4). Moreover three of them contain starting tetranuclear core {Li2Zn2} and saves its geometry. We also demonstrate the influence of substituent in terephthalate ring on preservation of tetranuclear core. For compound 1 it was shown that luminescence of the framework could be quenched when nitrobenzene is included in the pores.

Multisubstituted C2-symmetric ansa-metallocenes bearing nitrogen heterocycles: influence of substituents on catalytic properties in propylene polymerization at higher temperatures

In this work we systematically studied the effects of modifications of substituents on the performance of the isospecific zirconocene-based catalyst family, Me2Si(2-Alk-4-(N-carbazolyl)Ind)ZrX2 (X = Cl, Me), wherein the progenitor was shown to be particularly suitable in high-temperature propylene polymerization processes. In order to obtain the required zirconocenes, we developed a novel synthetic pathway to 4-(N-carbazolyl)indenes through Pd-catalyzed cyclizations of 2,2'-dibromobiaryls with 4-aminoindenes, which were synthesized via Buchwald-Hartwig reaction or electrophilic amination of 4-indenyl Grignard reagents with trimethylsilylmethyl azide. By a number of examples, the anion-promoted rac-to-meso isomerization method was shown to work reliably well for preparation of rac-ZrMe2-complexes. Certain zirconocenes among the 21 tested in propylene polymerization at 70 and 100 °C under MAO or borate activation outperformed the parent catalyst in molecular weight capability, regio- or stereoselectivity.

Ethylene Trimerization over Supported SNS and PNP

ABSTRACT Chromium(III) complexes with sulphur, nitrogen and phosphorus tridentate ligands were synthesized and characterized. These complexes were supported on SiO2 and characterized by BET surface area measurements, XRF, SEM-EDX and FTIR. The complexes were tested for activity and selectivity in the trimerization of ethylene. The substituent's effect and influence on the sulphur on the supported catalysts were studied using the ethyl and the decyl substituted catalysts. The influence of temperature on catalytic performance was evaluated using the PPP supported system. The most active supported catalyst, the decyl substituted SNS catalyst, showed good activity of up to 19 500 g/g Cr h-1 and selectivity of 97.3 % to C6 products (98.2 % 1-hexene). This activity and selectivity were comparable to the homogeneous counterpart's performance that achieved 22 000 g/g Cr h-1 and 98.2 % C6 products (96.7 % 1-hexene), which surpassed the ethyl substituted catalyst, which was not supported, under the same reaction conditions. The supported PPP catalyst activities showed it was sensitive to higher temperatures, but this depends on the supporting technique. Keywords: Ethylene trimerization, sulfanyl ligands, phosphine ligands, supported catalysts.

A photoelectron imaging study of the deprotonated GFP chromophore anion and RNA fluorescent tags.

Green fluorescent protein (GFP), together with its family of variants, is the most widely used fluorescent protein for in vivo imaging. Numerous spectroscopic studies of the isolated GFP chromophore have been aimed at understanding the electronic properties of GFP. Here, we build on earlier work [A. V. Bochenkova, C. Mooney, M. A. Parkes, J. Woodhouse, L. Zhang, R. Lewin, J. M. Ward, H. Hailes, L. H. Andersen and H. H. Fielding, Chem. Sci., 2017, 8, 3154] investigating the impact of fluorine and methoxy substituents that have been employed to tune the electronic structure of the GFP chromophore for use as fluorescent RNA tags. We present photoelectron spectra following photoexcitation over a broad range of wavelengths (364-230 nm) together with photoelectron angular distributions following photoexcitation at 364 nm, which are interpreted with the aid of quantum chemistry calculations. The results support the earlier high-level quantum chemistry calculations that predicted how fluorine and methoxy substituents tune the electronic structure and we find evidence to suggest that the methoxy substituents enhance internal conversion, most likely from the 2ππ* state which has predominantly Feshbach resonance character, to the 1ππ* state.

Study of Crystallization and Composition on Silicon Oxycarbide (SiOC) and Silicon Boron Oxycarbide (SiBOC) Ceramics Obtained from Alkoxysilanes Precursors

This work deals on the preparation of silicon oxycarbide (SiOC) and silicon boron oxycarbide (SiBOC) ceramics from pyrolysis involving alkoxysilanes with different organic groups. Boron content, organic substituent and annealing time were evaluated on crystallization and composition of resulting ceramics. B-free precursors composed of methyltriethoxysilane (MTES), phenyltriethoxysilane (PTES) and vinyltrimethoxysilane (VTMS) were obtained by the sol-gel method, whilst B-containing precursors were prepared by adding to each alkoxysilane a proper amount of boric acid resulting in B/Si atomic ratios of 0.1 and 0.5. Precursors were pyrolyzed at 1500 °C for 1 and 3 h to produce respective SiOC and SiBOC ceramics. X-ray diffraction (XRD) patterns revealed enhanced SiC phase crystallization for PTES-derived ceramics, followed by those containing vinyl and methyl groups, which was also confirmed by X-ray photoelectron spectroscopy (XPS) from percentages of Si-C and Si-O bonds. Csp2 and Csp3 amounts varied among ceramics, indicating direct influence of organic substituent on conductive carbon phase development. Boron addition induced the growth of SiC crystallites, having more evident effect in matrices with higher proportions of amorphous fraction and lower residual carbon amounts. Organic group nature, boron content and annealing time played an important role for production and evolution of SiC and C phases into ceramics.

Eight coordinated mononuclear dysprosium complexes of heptadentate aminophenol ligands: the influence of the phenol substituents and the ancillary donors on the magnetic relaxation.

The mononuclear complexes [Dy(3Br,5Cl-H3L1,1,4)(D)]·solvate (D = H2O, solvate = 0.25MeOH, 1W·0.25MeOH; D = Py without solvate, 1Py), and [Dy(3NO2,5Br-H3L1,1,4)(H2O)] (2W) were isolated. The crystal structures of 1W·0.25MeOH, 1Py and 2W·2CH3C6H5 show that the DyIII ion is octacoordinated, in N4O4 or N5O3 environments, with distorted geometries, between square antiprism, biaugmented trigonal prism and triangular dodecahedral. A similar environment for the metal ion is shown in the chiral crystals of the diamagnetic yttrium analogue [Y(3Br,5Cl-H3L1,1,4)(MeOH)] (3M), which were spontaneously resolved. Magnetic analyses of the three dysprosium complexes, and their diluted analogous 1W@Y, 1Py@Y and 2W@Y, reveal that none of them seem to relax through an Orbach mechanism at Hdc = 0. However, the three complexes show Orbach relaxation under Hdc = 1000 Oe, and 1Py is the in-field SIM with the highest energy barrier among these complexes, with a Ueff value of 358 K. Analysis of ac magnetic data shows that the electron-withdrawing substituents on the phenol rings of the aminophenol ligands, as well as the auxiliary oxygen donors from water ligands, reduce the energy barriers of the complexes, which is attributed to a charge reduction in the coordinating atoms of the aminophenol donor. Ab initio calculations support the experimental results.

Tuning the luminescence efficiency by perfluorination of side chains in Eu3+ complexes with β-diketones of the thiophene series.

A series of europium and gadolinium complexes comprising a β-diketone moiety modified with a fluorinated side-group and thiophene ring have been designed and synthesized and a comparative study of their luminescence properties has been carried out. In this study, when the methyl side group was modified by sequential addition of fluorine substituents and then the perfluorinated carbon chain was extended up to n-C8F17 by adding CF2 fragments, it transpired that the non-radiative energy processes are significantly suppressed in structurally more rigid polyfluorinated β-diketonate compounds of the series as C-H oscillators are replaced with low-energy C-F oscillators. The impact of other electron-withdrawing and electron-donating substituents on the spectroscopic and photophysical properties of the complexes in the present study has also been observed. Despite the presence of low-lying ligand-to-metal charge transfer states, the fluorinated Eu3+ complexes proved to be bright luminophores capable of delivering ca. 50% quantum yield under UV radiation. The role of fluorination and carbon chain length was examined by using experimental spectroscopic methods and the results obtained were largely in good agreement with theoretical calculations (Judd-Ofelt theory analysis, and semiempirical quantum chemistry calculations) supporting our key experimental findings.

Influence of C5‐Substituents on Repair of O4‐Methyl Adducts of Pyrimidines by O6‐Alkylguanine DNA Alkyltransferases

AbstractThe DNA repair protein O6‐alkylguanine‐DNA alkyltransferase (AGT), found in numerous organisms, can remove methyl groups from the O6‐ and O4‐atoms of 2′‐deoxyguanosine and thymidine in DNA. AGT variants demonstrate different repair efficiencies towards these lesions. To understand the influence of C5 nucleobase substituents on O4‐methyl removal by AGTs, DNA duplexes containing 5‐chloro‐, 5‐bromo‐ 5‐iodo‐ and 5‐trifluoromethyl‐O4‐methyl‐2′‐deoxyuridine were studied. UV thermal denaturation revealed a stability reduction of 11 °C for the O4‐methyl halogen series and 5‐trifluoromethyl analog relative to their controls. For the 5‐chloro analog efficient repair was observed by human and E.coli AGTs. For the larger halogens (5‐bromo and 5‐iodo) and 5‐trifluoromethyl analog, human AGT showed moderate repair of the O4‐methyl adduct. E.coli OGT and Ada‐C readily repaired most adducts with reduced efficiency for the larger groups, except C5‐iodo. These results suggest electronic contributions and favourable interactions of the C5‐halogens within the AGT active site contribute to efficient dealkylation.

Ferrocenyl Migrations and Molecular Rearrangements: The Significance of Electronic Charge Delocalization

The enhanced stabilization of a carbocationic site adjacent to a ferrocenyl moiety was recognized within a few years of the discovery of sandwich compounds. While a detailed understanding of the phenomenon was the subject of some early debate, researchers soon took advantage of it to control the ease and direction of a wide range of molecular rearrangements. We, here, discuss the progress in this area from the pioneering studies of the 1960s, to more recent applications in chromatography and analytical detection techniques, and currently in the realm of bioactive organometallic complexes. Several classic reactions involving ferrocenyl migrations, such as the pinacol, Wolff, Beckmann, and Curtius, are discussed, as well as the influence of the ferrocenyl substituent on the mechanisms of the Nazarov, Meyer-Schuster, benzoin, and Stevens rearrangements. The preparation and isomerizations of ferrocenyl-stabilized vinyl cations and vinylcyclopropenes, together with the specific cyclization of acetylcyclopentadienyl-metal derivatives to form 1,3,5-substituted benzenes, demonstrate the versatility and generality of this approach.

Influence of substituents in 1,10-phenanthroline on the structural and photophysical properties of W(CO)4(1,10-phenanthroline-type) complexes

In this work, methyl and phenyl substituents were introduced in the 2,9- and 4,7-positions of the phen ligand in order to study its impact on the structural and photophysical properties of [W(CO)4(phen-type)] complexes [phen-type = 4,7-dimethyl-1,10-phenanthroline (4,7-DMPhen); 4,7-diphenyl-1,10-phenanthroline (BPhen), and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)]. Crystallographic analysis of these complexes allows to investigate the correlation between the geometrical parameters with their photophysical properties measured by steady-state and time-resolved spectroscopies. The (OC)eq–W–(CO)eq angle is the most significantly influenced geometrical parameter by the substituents, showing values of 92.5°, 90.2°, and 81.2° for [W(CO)4(4,7-DMPhen)], [W(CO)4(BPhen)], and [W(CO)4(BCP)], respectively. The smallest angle observed for [W(CO)4(BCP)] is attributed to a steric repulsion exerted by the methyl groups to the equatorial carbonyls. Remarkably, a smaller OCeq–W–COeq angle favors the High-Energy (HE) emission band, as evidenced in the photoluminescence (PL) spectra of [W(CO)4(BCP)]. Conversely, a greater angle favors the Low-Energy (LE) emission band, as observed in the PL spectra of [W(CO)4(4,7-DMPhen)] and [W(CO)4(BPhen)]. The PL lifetime of the LE emission band becomes shorter when decreasing the (OC)eq–W–(CO)eq angle. Furthermore, the absorption feature was affected by the 2,9-dimethyl substituents, showing greater contribution from the high-energy shoulder on the visible absorption band. This study shows that the perturbation of the (OC)eq–W–(CO)eq angle induced by the substituents in the phen ligand influences on the photophysical properties of [W(CO)4(phen-type)] complexes.

Exploring the Substituent Еffect on the Structure and Еlectronic Рroperties of Si2(para-C6H4X)2 Мolecules

Substituent effect on the structure and electronic properties of the Si2(para-C6H4X)2 molecules (X = NH2, OH, Me, H, F, Cl, CN, NO2) were studied at wB97XD/6-311G(d,p) level of theory. The substituent effect on the structural parameters, reactivity parameters (hardness, chemical potential and electrophilicity) and 29Si NMR chemical shift was explored. Stability of the Si(para-C6H4X) fragments were investigated in the doublet and quartet states for illustration of the Si≡Si bond character. Substituent influence on the stability of these different spin multiplicities of Si(para-C6H4X) fragments was investigated. The Si–Si bonding situation in the studied molecules was examined via the Shubin Liu’s energy decomposition analysis (EDA-SBL), adaptive natural density partitioning (AdNDP), and Quantum theory of atoms in molecules (QTAIM) schemes.

1-Naphthols as components for multifunctional material systems (MFMS): the molecular modeling approach

Increasing research interests have been paid to developing efficient multifunctional material systems (MFMS) by using various composite materials, owing to their useful properties and good stability. Here, we systematically studied 1-naphthols, especially how the type and position of a substituent influence the reactivity and properties, using different electron-directing groups. During computations, important preparation guidelines for thiol derivatives of 1-naphthol were obtained. It is very interesting to note that some molecules could exhibit intramolecular O–H–O interactions. Careful theoretical investigation reveals that all the tested compounds are stable and the molecules with substituents in positions 4 and 8 are the least reactive. It is also worth noting that for the stability and polarizability tensor values, it is more favorable when both substituents are in the same benzene ring. Among tested 1-naphthols, the greatest values of alpha, beta, and gamma are more than 5, 60, and 110 times better respectively, than in the urea molecule; the change of electron-withdrawing group (EWG) to electron-donating group (EDG) increases NLO effects. This study provided a new scope of 1-naphthols applicability by using them as anti-corrosion materials and as very good materials for NLO devices due to the high stability of the aromatic structure coupled with polarity given by the substituents. Also, the understanding of IR vibrations for more complex organic compounds with thiol substituent has been improved.

Influence of Cyano Substituents on the Electron Density and Catalytic Activity Towards the Oxygen Reduction Reaction for Iron Phthalocyanine

Iron(II) 2,3,9,10,16,17,23,24-octa(cyano)phthalocyanine (OCNFePc), was tested as a catalyst for the oxygen reduction reaction (ORR) adsorbed on carbon nanotubes. The composite was analyzed spectroscopically and electrochemically characterized at pH 13 and pH 1. The composite showed close to 4 electron processes at pH 13. Computational analysis indicates that the O2 molecule binds end-on to the metal center and that the dioxygen molecule is dissociated on both the Fe metal center and the corral ring. An Analysis of the molecular electrostatic potential confirms the behavior of cyano residues as electron-withdrawing moieties in OCNFePc. As a result of its catalytic behavior and theoretical analysis of its O2 binding energy, OCNFePc was placed in a high position on a volcano correlation of similar phthalocyanine composites.

Influence of substituent and push‐pull effect on the chemical shifts of the carbon in bridging bond of 1‐furyl/thienyl‐2‐arylethylene

AbstractSixty‐six samples of 1‐furyl/thienyl‐2‐arylethylene model compounds XCHCHArY (abbreviated XEBY) were synthesized. The nuclear magnetic resonance spectra (NMR) of model compounds were determined. The chemical shift δC(X) and δC(Y) of the carbon atoms in bridging bond CHCH which connected to the X group and the ArY group, respectively, were confirmed with the two‐dimensional NMR method. The effect of substituent on the δC(X) and δC(Y) was studied, meanwhile, the push‐pull effect of substituent on ΔδC = δC(Y) − δC(X) and δC(Y/X) = δC(Y)/δC(X) were discussed. The results show the following: (a) Both the δC(X) and δC(Y) are affected by excited‐state substituent constant of group X, Hammett constant σ(Y), and excited‐state substituent constant of group Y. The effect of σ(Y) on the δC(X) is positive, whereas that on the δC(Y) is negative. That is to say, the σ(Y) of group Y has an alternative influence on the δC(X) and δC(Y). (b) Compared with furyl, there is a p‐d effect formed by the 3d orbit of S atom and the p electron of the π system in thienyl, which increase the chemical shift of the carbon atoms in bridging bond. (c) The push‐pull effect between substituent X and Y is not only affected by the σ parameter but also related to the parameter, which results from the combined effect of the two parameters σ and . The observation of this paper provides a new perspective in understanding the push‐pull effect of substituent.