Cisoid Structure Research Articles

High-performance pure red perovskite light-emitting diodes utilizing conformational transformation of ionic liquid additive

The performance of perovskite light-emitting diodes (PeLEDs) depends highly on the defect density and carrier transport properties of the perovskite layer. Some long-chain ligands are good at passivating the defects, but they hinder the charge injection into the perovskite because of their insulating nature. Notably, red PeLEDs suffer from spectral shift under bias caused by ion migration inside the mixed cation perovskite layer. This study proposes the use of silver bis(trifluoromethanesulfonyl)imide (AgTFSI) a conducting ionic liquid as a multifunctional additive to the perovskite to overcome the aforementioned problems. The TFSI anion comprises strong electronegative -CF3 and Lewis base -SO2 groups. These functional groups interact with undercoordinated Pb2+, efficiently suppressing defects and reducing nonradiative recombination in the perovskite film. AgTFSI displays two distinct conformations: cisoid and transoid. The opposing orientations of the two functional groups enable the cisoid structure to exclusively engage with the perovskite through the -SO2 groups. In contrast, the semi-linear arrangement of the transoid structure provides accessibility to both -SO2 and -CF3 groups for interaction. Owing to their conformational flexibility, the TFSI anions in AgTFSI undergo a transition from the zigzag cisoid to a more linear transoid structure when added to the perovskite, enabling efficient packing and tight binding with the Pb defects. As a result, the perovskite film shows a twofold increase in photoluminescence quantum yield and decay lifetime. Consequently, the red PeLEDs achieve a maximum external quantum efficiency of 13.52%, nearly double that of the control device. This study confirms AgTFSI's potential as an effective additive for high-performance pure red PeLEDs.

Ultrafast time resolved spectroscopic studies on the generation of the ketyl-sugar biradical by intramolecular hydrogen abstraction among ketoprofen and purine nucleoside dyads.

Intramolecular hydrogen abstraction reactions among ketoprofen (KP) and purine nucleoside dyads have been proposed to form ketyl-sugar biradical intermediates in acetonitrile. Femtosecond transient absorption studies on KP and purine nucleoside dyads reveal that the triplet state of the KP moiety of the dyads with cisoid structure decay faster (due to an intramolecular hydrogen abstraction reaction to produce a ketyl-sugar biradical intermediate) than the triplet state of the KP moiety of the dyads with transoid structure detected in acetonitrile solvent. For the cisoid 5-KP-dG dyad, the triplet state of the KP moiety decays too fast to be observed by ns-TR(3); only the ketyl-sugar biradical intermediates are detected by ns-TR(3) in acetonitrile. For the cisoid 5-KP-dA dyad, the triplet states of the KP moiety could be observed at early nanosecond delay times, and then it quickly undergoes intramolecular hydrogen abstraction to produce a ketyl-sugar biradical intermediate. For the cisoid 5-KPGly-dA and transoid 3-KP-dA dyads, the triplet state of the KP moiety had a longer lifetime due to the long distance chain between the KP moiety and the purine nucleoside (5-KPGly-dA) and the transoid structure (3-KP-dA). The experimental and computational results suggest that the ketyl-sugar biradical intermediate is generated with a higher efficiency for the cisoid dyad. However, the transoid dyad exhibits similar photochemistry behavior as the KP molecule, and no ketyl-sugar biradical intermediate was observed in the ns-TR(3) experiments for the transoid 3-KP-dA dyad.

Helix oscillation of polyacetylene esters detected by dynamic 1H NMR, IR, and UV-vis methods in solution

An aliphatic substituted acetylene, n-heptyl propiolate, was stereoregularly polymerised using a catalyst, [Rh(nbd)Cl]2, at 40 °C in methanol to obtain the corresponding helical polymer, PnHepP. The changes in the line shapes and splitting patterns of the 1H NMR spectra were interpreted consistently as representing restricted rotation around the ester O–Ce bond in –O–CeHe2(R)– (R = n-hexyl alkyl chains), rather than helix inversion, with the aid of a 3-site jump model. A two-line peak corresponding to the ester methylene protons of –O–CH2– observed at 30 °C suggested the formation of three rotamers designated as A, B, and C based on the presence of contracted helix and stretched helix forms, each of which has an intrinsic helical pitch with a helical cis–cisoid structure. Furthermore, an accordion-like helix oscillation (HELIOS) along the main chain axis was proposed to explain the temperature dependence of spectral changes observed in the 1H NMR, UV-vis, and IR spectra. The temperature dependence of the UV-vis and 1H NMR spectra of PnHepP corroborated the presence of contracted and stretched one-handed helix sense polymers in solution.

Synthesis and Properties of Thiophene‐Fused Benzocarborane

The o-carborane-based π-conjugated compound, benzocarborano- [2,1-b:3,4-b']dithiophene was synthesized. Its crystal structure revealed high coplanarity for the two thiophene rings of the 2,2'-bithiophene skeleton, which is fixed in the cisoid structure by the o-carborane unit. Theoretical calculations indicated non-aromaticity for its center C(6) ring moiety as well as decreased HOMO and LUMO levels. The o-carborane moiety provides an electron-withdrawing character to the 2,2'-bithiophene unit through an inductive effect.

Syntheses, Dynamic Behaviour and Theoretical Studies of [(Piperidinomethyl)silyl]methyl‐Cyclopalladated Dimetallic Complexes

AbstractThe cationic complex [Pd{CH2SiPh2(CH2NC5H10)‐κ2C,N}(NCMe)2]BF4 (CH2NC5H10 = piperidinomethyl) is obtained from the reaction of [Pd{CH2SiPh2(CH2NC5H10)‐κ2C,N}(μ‐Cl)]2 with TlBF4 in the presence of NCMe. It reacts with KO2CCH3 leading to the dimetallic complex [Pd{CH2SiPh2(CH2NC5H10)‐κ2C,N}(μ‐O2CCH3‐κO:κ′O)]2, which exists only as the transoid isomer in solution. A dynamic process due to inversion of the acetato bridges is detected by variable‐temperature 1H NMR spectroscopy. The reaction of the same parent complex with Kdmpz (dmpz = dimethylpyrazolate) leads to the dinuclear complex [Pd{CH2SiPh2(CH2NC5H10)‐κ2C,N}(μ‐dmpz‐κN:κ′N)]2, which in solution exists as a mixture of cisoid and transoid isomers, but no inversion of the bridging pyrazolato groups has been observed. The reaction between equimolar amounts of these two complexes in CH2Cl2 affords low yields of the expected mixed acetato/pyrazolato‐bridged complex [Pd2{CH2SiPh2(CH2NC5H10)‐κ2C,N}2(μ‐O2CCH3‐κO:κ′O)(μ‐dmpz‐κN:κ′N)]. The mixed chlorido‐pyrazolato‐bridged complex [Pd2{CH2SiPh2(CH2NC5H10)‐κ2C,N}2(μ‐Cl)(μ‐dmpz‐κN:κ′N)] is obtained by mixing equimolar amounts of the parent dichlorido‐ and bis(dimethylpyrazolato)‐bridged dinuclear complexes, and exhibits a dynamic process in solution corresponding to the inversion of the bridges. Only the cisoid isomers are detected for both dimetallic complexes with mixed bridging ligands. The experimental findings of the preferred transoid or cisoid structure in these dinuclear Pd complexes were supported by quantum chemical calculations.

Multidentate Pyridyl‐Based Ligands in the Coordination‐Driven Self‐Assembly of Palladium Metallo‐Macrocycles

AbstractIn the current study, a convenient way is presented to synthesize one ditopic and two tetratopic pyridine‐based ligands, which are then used to construct metallo‐supramolecular polygons. The tetratopic ligands offer two different metal‐binding sites, one central 2,2′‐bipyridine, which can act as a chelate ligand, and two separate pyridine rings, which mediate assembly formation. The three ligands differ with respect to their conformational flexibility. While a biphenyl core allows the ligand to adjust its conformation as needed, a bipyridine core strongly prefers a divergent arrangement of the additional pyridine binding sites, but can be fixed in a cisoid conformation by metal complexation to the bipyridine.Instead, a phenanthroline core already fixes the pyridinylethynyl substituents in a cisoid structure without any metal coordinated to it. Upon mixing each one of the ligands separately with the appropriate amount of dpppPdII triflate, discrete self‐assembled metallo‐macrocycles are formed which are characterized by 1H and 31P NMR spectroscopy and mass spectrometry. Mixing all three ligands simultaneously with the metal complex leads to the formation of a statistical dynamic combinatorial library (DCL) of all possible homo‐ and heterodimeric metallo‐supramolecular assemblies. This underlines the conformational differences between the three ligands not to impact significantly on the self‐assembly process.

X-ray and spectroscopy studies of antisymbiotic effect O-coordination of the 4-methoxy benzoyl methylene triphenyl phosphorane ligand in palladium(II) complex

Complex [Pd(C 6H 4CH 2NH 2–k 2-C,N)(Py)(OC (MeO-4-C 6H 4) CH-PPh 3)]OTf (1) (OTf = CF3SO3) represents the example of an ylide O-bound to a Pd(II) center that is unusual for the classical soft metals. O-coordination of ylides and cisoid structure of complex was demonstrated by single-crystal X-ray analyses and spectroscopy. The IR and NMR data of the product (1), formed by the reaction of Pd(II) with the same ylide, are similar to those of O-bounded ylide. Analytical data indicate a 1:1 stoichiometry between the ylide and Pd (II) in the product ( 1). The molar conductivity of (1) Λ = 175 Ω −1 mol −1 cm 2 is within the range for 1:1electrolytes.

Toward poly(aminophthalimide), structures of dimers and trimers

Poly(aminophthalimide) (PAP) dimers and trimers have been synthesized by palladium-catalyzed cross-coupling reactions of 3-aminophthalimides with 3-chloro- and 3,6-dichlorophthalimide, respectively. When Pd(OAc) 2, XPhos (2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl), and K 3PO 4 are used, the C–N bond-forming reactions proceed quantitatively. The structures of those oligomers are examined by experimental and theoretical techniques including NMR, IR, single-crystal X-ray diffraction, and DFT calculations. The strong preference for cisoid structure of the diphthalimidylamine unit bearing a bifurcate hydrogen bonding is disclosed. Therefore, the aminophthalimide backbone is a highly promising candidate for the construction of a dynamically ordered helical structure.

Restricted Rotation in Unbridged Sandwich Complexes: Rotational Behavior of closo‐[Co(η5‐NC4H4)(C2B9H11)] Derivatives

Rotation about the centroid/metal/centroid axis in ferrocene is facile; the activation energy is 1-5 kcal mol(-1). The structurally similar sandwich complexes derived from closo-[3-Co(eta5-NC4H4)-1,2-C2B9H11] (1) have a different rotational habit. In 1, the cis rotamer in which the pyrrolyl nitrogen atom bisects the carboranyl cluster atoms is 3.5 kcal mol(-1) more stable in energy than the rotamer that is second lowest in energy. This cis rotamer is wide, spanning 216 degrees , and may be split into three rotamers of almost equal energy by substituting the N and the carboranyl carbon atoms adequately. To support this statement, closo-[3-Co(eta5-NC4H4)-1,2-(CH3)2-1,2-C2B9H9] (2), closo-[3-Co(eta5-NC4H4)-1,2-(mu-CH2)3-1,2-C2B9H9] 3, 2-->BF3, and 3-->BF3 have been prepared. Two rotamers are found at low temperature for 2-->BF(3) and 3-->BF3. Compounds 2, 3, and 1-->BF3 behave similarly to 1. Rotational energy barriers and the relative populations of the different energy states are calculated from 1H DNMR spectroscopy (DNMR, dynamic NMR). These results agree with those of semiempirical calculations. Without exception, the cis rotamer is energetically the more stable. The fixed conformation of 1 assists in elucidating the rotational preferences of the [3,3'-Co(1,2-C2B9H11)2]- ion in the absence of steric hindrance; the [3,3'-Co(1,2-C2B9H11)2]- ion is commonly accepted to present a cisoid orientation. Complex 1 is electronically similar to the [3,3'-Co(1,2-C2B9H11)2]- ion. Both have heteroatoms in the pi ligands, and they have the same electronegativity difference between the constituent atoms. This leads to a view of the [NC4H4]- as [7,8-C2B9H11]2- ion, with no steric implications. Therefore the [3,3'-Co(1,2-C2B9H11)2]- ion should be considered to have a cisoid structure, and the different rotamers observed to be the result of steric factors and of the interaction of the counterion with either B-H groups and/or ancillary ligands. The rotamer adopted is the one with the atoms holding the negative charges furthest apart.

2,2'-Bithiophene-5-carbaldehyde

The structure of 2,2'-bithiophene-5-carbaldehyde, C 9 H 6 OS 2 , has been determined and shows a predominantly cisoid structure for the bithiophene rings

Calculations of the electronic structure of various aperiodic polymers by an elongation method

AbstractAn elongation method, which had already been proposed to calculate the electronic structure of aperiodic polymer efficiently, was applied to atactic polypropylene, with the approximation level of the extended Hückel method. The atomic populations thus calculated were found to be dependent sensitively on the tacticity of the polymer. Next, this elongation method was applied to the π‐electron stacking system composed of ethylene and butadiene, etc. Excellent agreement was found between the elongation method and the usual extended Hückel calculations. Thus, the elongation method can confidently be applied to π‐electron molecular crystal systems. Finally, the local density of states of polyacetylene with both cis–transoid and trans–cisoid structures was calculated. We found that the site with large local density of state in the valence band of a polymer chain gives large electron transfer to the site with large local density of state in the conduction band of another polymer chain. © 1994 John Wiley & Sons, Inc.

Experimental and theoretical studies of alkaline-earth metal coordination: x-ray crystal structures of calcium, strontium, and barium carbazoles and ab initio model calculations

The solid-state structures of the aromatic alkaline-earth metal amides (N-~arbazolyl),Ca(pyridine)~ (l), (N-car- bazolyl),Sr(NH,)(DME), (2) (DME = 1,2-dimethoxyethane), and (N-carbazolyl),Ba(DME), (3) are compared. Compounds 1-3 crystallize as monomers with the M2+ cation (M = Ca, Sr, Ba) a-bound to the carbazole nitrogen atoms. This is in contrast to the dimeric alkali metal carbazoles, which exhibit varying degrees of polyhapto bonding to the carbazole mystem. While the metal coordination smoothly increases from six to seven to eight with M = Ca, Sr, Ba, respectively, the orientation of the anionic carbazole ligands changes from cisoid with M = Ca, Sr to transoid with M = Ba. Ab initio calculations on a series of solvated and unsolvated model complexes indicate this to be due to covalent Ba-N a-bonding contributions involving metal d-orbitals and to cation polarization. These factors favor bent X-Ba-X arrangements, both in naked BaX, compounds and in solvated complexes BaX,(L),. Anion-anion repulsion prevents cisoid structures for the complexes of the smaller Ca and Sr cations. Crystal data for 1: monoclinic space group P2,/c, Z = 4, u = 12.723 (6) A, b = 18.169 (13) A, c = 22.348

Detection of diastereoisomers of metallacyclobutane intermediates in the metathesis polymerization of norbornene and its derivatives

Addition of norbornene derivatives to racemic mixtures of chiral tungsten–carbene complexes is shown to lead to the formation of transoid diastereoisomeric tungstacyclobutanes that can be distinguished by 1H n.m.r. spectroscopy; cisoid structures, though formed, are too unstable to be observed.

Some aspects of the chemistry of polyfluoroalkadienes and polyfluoroalkatrienes

A convenient route for syntheses of perfluoro derivatives of 1,3-butadiene, 1,3,5-hexatriene, 1,4,7-octatriene and 1,4, 6,9-decatetraene as well as 2-chloropentafluoro-1,3-butadiene, 2,3-dichlorotetrafluoro-1,3-butadiene and 3-chlorononafluoro- 1,5-hexadiene based on the photochemical addition of fluorohalogenoethanes to fluorohalogenoethylenes is demonstrated. The reactions of dienes and trienes with alkoxides or diethylamine were studied and the stereochemistry of the products discussed. It was confirmed that the prepared compounds of 1,4-disubstituted tetrafluoro-1,3-butadiene type have a non planar cisoid structure. The reactions of 3-chlorononafluoro-1,5-hexadiene with a series of nucleophiles (Cl −, Br −, I −, F −, CN −, RO −, Et 2NH, Et 3N) show a different reactivity of both reactive centers. The perfluoroallyl chloride system in diene is of higher reactivity then the trifluorovinyl group and its reaction with a nucleophile proceeds via S N2 mechanism with an allylic rearrangement giving trans -isomer only. On the contrary, the trifluorovinyl group reacts obviously through a carbanion intermediate giving a mixture of cis - and trans -isomer as shown in reaction with an excess of alkoxide or diethylamine.

Structural and dynamic behaviour of complexes of lead(II) with two tetra-aza macrocyclic ligands as studied by X-ray crystallography and natural-abundance carbon-13 and nitrogen-15 nuclear magnetic resonance spectroscopy

Two complexes of the type [PbL][NO3]2, where L = La= 1,4,8,11-tetra-azacyclotetradecane or Lb= 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane, have been investigated by n.m.r. techniques in dimethyl sulphoxide (dmso) solution. The complex where L = La is interpreted as adopting a cis-octahedral geometry with a folded macrocyclic ligand. This geometry is confirmed by an X-ray analysis which also identifies unsymmetrical bidentate nitrate ions in cis positions. The asymmetry of these groups is probably caused by the lone pair on PbII. The complex crystallises in the monoclinic space group P21/c, Z= 4, with a= 10.326(2), b= 11.145(3), c= 14.832(4)A, and β= 96.19(2)°. 1 909 Reflections with I/σ(I) > 3.0 have been recorded on a four-circle diffractometer and least-squares refinement produced a final R of 0.049. The n.m.r. data reveal high-temperature, dynamic, conformational changes, and two strikingly different 1J(207Pb–15N) coupling constants (207.5 and 19.8 Hz) at low temperatures. The dynamic process, with ΔH‡= 110 ± 10 kJ mol–1 and ΔS‡= 105 ± 20 J K–1 mol–1, is interpreted as an intramolecular rearrangement between two identical cisoid structures, while the differing coupling constants for axial and equatorial nitrogen atoms are believed to be a consequence of the axial distortion observed in the crystal structure. When L = Lb the complex is not very stable in dmso (K= 1.31 dm3 mol–1 at 298 K) and macrocycle exchange is found to occur at ambient temperatures (ΔH‡= 38.5 ± 0.7 kJ mol–1, ΔS‡=–70 ± 3 J K–1 mol–1). The structure and behaviour of both complexes are discussed in relation to the ionic radius of the lead(II) ion.

Structure of the tetra-azacyclotetradecadienes obtained from α,β-enones and ethylenediamine

The tetra-azacyclotetradecadiene obtained from ethylenediamine and benzylideneacetone has the cisoid structure (I) while that obtained from ethylenediamine monoperchlorate and mesityl oxide has the transoid structure (IV).

Die NO‐katalysierte Isomerisierung von 2,6‐Dimethyl‐1, trans‐3,6‐heptatrien in der Gasphase

AbstractThe nitric oxide catalyzed isomerization of 2,6‐dimethyl‐1, trans‐3,6‐heptatriene has been measured for temperatures ranging between 209.1 and 311.4°C. The reaction follows second order kinetics and appears to be truly homogeneous. The main products are 1.5.5‐trimethyl‐1.3‐cyclohexadiene (1,5,5‐TCHD), 2.6.6‐trimethyl‐1.3‐cyclohexadiene (2,6,6‐TCHD) and 2.6‐dimethyl‐1, trans‐3.5‐heptatriene. Only traces of the cisoid structures of the linear trienes are detected, in equilibrium with the trans‐isomers, which is attributed primarily to a loss of conjugation energy in the cis‐isomer. The least squares regression analysis yields for the overall rate constants the ARRHENIUS equation log k (1/mole‐s) = (7.78 ± 0.14) − (25340 ± 350) /2.303 RT (°K). The analysis of the rate data shows that the reaction proceeds via a NO catalyzed geometrical isomerization followed by a thermal intramolecular 1,5‐hydrogen transfer and subsequent cyclization of the 1, cis‐3. 5‐triene structure. No competition with abstraction of the «triallylic» hydrogen by NO is observed.