Cross-conjugated Research Articles

Unusual Cross-Conjugation in Cyclic Dipeptide-Based Building Blocks for Donor-Acceptor Semiconducting Conjugated Polymers.

Cross conjugation, though prevalent in many organic compounds, is typically considered less effective for electron delocalization compared to linear conjugation. Consequently, it is rarely used as the backbone structure for semiconducting conjugated polymers. In this study, we designed and synthesized a novel building block, TIDP, which features a central cyclic dipeptide with cross conjugation characteristics. Strong intramolecular hydrogen bonding interactions confer TIDP with a highly rigid and coplanar conformation. Importantly, theoretical calculations reveal that π electrons are well delocalized across the entire structure, despite its low aromaticity. Conjugated polymers incorporating TIDP exhibit high charge carrier mobilities, demonstrating the effective π electrons delocalization of this innovative building block. Our findings show that with rational design, cross conjugation can achieve effective π electrons delocalization, providing a valuable approach for developing high-performance conjugated polymers for organic electronic materials.

Unusual Cross‐Conjugation in Cyclic Dipeptide‐Based Building Blocks for Donor–Acceptor Semiconducting Conjugated Polymers

AbstractCross conjugation, though prevalent in many organic compounds, is typically considered less effective for electron delocalization compared to linear conjugation. Consequently, it is rarely used as the backbone structure for semiconducting conjugated polymers. In this study, we designed and synthesized a novel building block, TIDP, which features a central cyclic dipeptide with cross conjugation characteristics. Strong intramolecular hydrogen bonding interactions confer TIDP with a highly rigid and coplanar conformation. Importantly, theoretical calculations reveal that π electrons are well delocalized across the entire structure, despite its low aromaticity. Conjugated polymers incorporating TIDP exhibit high charge carrier mobilities, demonstrating the effective π electrons delocalization of this innovative building block. Our findings show that with rational design, cross conjugation can achieve effective π electrons delocalization, providing a valuable approach for developing high‐performance conjugated polymers for organic electronic materials.

Tetra S-confused porphyrinoids.

Maximum confusion in porphyrinoids can be achieved by inter-linking heterocycles only through 2,4-connectivity. 20π confused porphycene and 30π expanded porphycene represent examples with the highest number of confused heterocyclic units in a given macrocycle. They significantly differ from the parent 20π porphycene and 30π hexaphyrin in their structural, electronic and redox properties due to the cross conjugation arising from the 2,4-connectivity of the heterocycle. They have been characterized by single crystal X-ray diffraction studies and their aromatic features have been substantiated by quantum chemical calculations.

Tricyclic Fused Lactams by Mukaiyama Cyclisation of Phthalimides and Evaluation of their Biological Activity.

We report that phthalimides may be cyclized using a Mukaiyama-type aldol coupling to give variously substituted fused lactam (1,2,3,9b-tetrahydro-5H-pyrrolo[2,1-a]isoindol-5-one) systems. This novel process shows a high level of regioselectivity for o-substituted phthalimides, dictated by steric and electronic factors, but not for m-substituted phthalimides. The initial aldol adduct is prone to elimination, giving 2,3-dihydro-5H-pyrrolo[2,1-a]isoindol-5-ones, and the initial cyclisation can be conducted in such a way that aldol cyclisation-elimination is achievable in a one-pot approach. The 2,3-dihydro-5H-pyrrolo[2,1-a]isoindol-5-ones possess cross conjugation and steric effects which significantly influence the reactivity of several functional groups, but conditions suitable for epoxidation, ester hydrolysis and amide formation, and reduction, which provide for ring manipulation, were identified. Many of the derived lactam systems, and especially the eliminated systems, show low solubility, which compromises biological activity, although in some cases, antibacterial and cytotoxic activity was found, and this new class of small molecule provides a useful skeleton for further elaboration and study.

Tectonic evolution of the Indio Hills segment of the San Andreas fault in southern California, southwestern USA

Abstract. Transpressional uplift domains of inverted Pliocene–Pleistocene basin fill along the San Andreas fault zone in Coachella Valley, southern California (USA), are characterized by fault linkage and segmentation and deformation partitioning. The Indio Hills wedge-shaped uplift block is located in between two boundary fault strands, the Indio Hills fault to the northeast and the main San Andreas fault to the southwest, which merge to the southeast. Uplift commenced about or later than 0.76 million years ago and involved progressive fold and faulting stages caused by a change from distributed strain to partly partitioned right-slip and reverse/thrust displacement on the bounding faults when approaching the fault junction. Major fold structures in the study area include oblique, right-stepping, partly overturned en echelon macro-folds that tighten and bend into parallelism with the Indio Hills fault to the east and become more open towards the main San Andreas fault to the west, indicating an early and close relationship of the macro-folds with the Indio Hills fault and a late initiation of the main San Andreas fault. Sets of strike-slip to reverse step-over and right- and left-lateral cross faults and conjugate kink bands affect the entire uplifted area, and locally offset the en echelon macro-folds. Comparison with the Mecca Hills and Durmid Hills uplifts farther southeast along strike in Coachella Valley reveals notable similarities, but also differences in fault architectures, spatial and temporal evolution, and deformation mechanisms. The present work contributes to better understand the structure and tectonic history of a major fault system along a transform plate boundary.

Removing the Destructive Quantum Interference in Cross Conjugation System by Structural Restraint

Removing the Destructive Quantum Interference in Cross Conjugation System by Structural Restraint

Morphotectonic evolution of the Quaternary landforms in the Yangui River basin in the Indo-Myanmar Range

The present study is an attempt to gain insight of the geodynamic implications on the evolution of Quaternary landforms in the Yangui River basin in the Indo-Myanmar Range (IMR), taking a multi-disciplinary approach. Originating at an elevation of ~2568 m asl, the Yangui River flows almost parallel to the regional strike of the IMR and drains into the Imphal valley at Yaripok and exhibits varied valley floor morphology. The valley floors are narrowest in the transverse valley sections. The fluvial landforms are represented by fill terraces, strath terraces and paleochannels. The chronologically constrained ages from fluvial stratigraphy suggests that the oldest phase of aggradation in the area began much before 8 ka. A total of 1164 lineaments were mapped, most trending NE-SW, which is slightly oblique to the regional strike of the IMR. East of the study area, the most prominent lineaments are those trending NE-SW. Lineament analysis suggests that the NNE-SSW trending lineaments are the first generation; followed by the ENE-SWS, while the youngest are the NW-SE trending lineaments. Quaternary landforms related to tectonic activity are observed in the Ringui area, where the morphology suggests transpressional tectonics. Cross-cutting relationships amongst faults suggest multiple phases of tectonic activity; linear valleys are observed along the fault planes. The cross conjugate faults and NW-SW lineaments of the area confirm tectonic activity in the area, which corroborates well with the seismogenic potential and oblique geometry of the Churachandpur-Mao Fault (CMF). Morphometric data also suggest ongoing tectonic activity in the area.

Electropolymerization, spectroelectrochemistry and electrochromic properties of cross-conjugated and conjugated selenophenothiophenes with thiophene bridge

Two novel selenophenothiophene homopolymers, P(SeT1) and P(SeT2), were electrochemically prepared for the first time from their corresponding monomers (i) conjugated 2,5-di(thiophen-2-yl)selenopheno[3,2-b]thiophene (1) and (ii) cross-conjugated 2,5-di(thiophen-2-yl)selenopheno[2,3-b]thiophene (2) to explore their electrochromic behaviors. The effects of conjugation and cross conjugation on the electrochromic performances and electrochemistry and spectroelectrochemistry of the polymers were systematically studied. While the cross conjugated polymer film of P(SeT2) displayed a color change from yellow to a light green upon oxidation, the conjugated polymer film of P(SeT1) showed an orange color in the neutral and a claret red in the oxidized state. The polymer P(SeT1), owing to its extended π-conjugation, had a lower optical band gap of 1.82 eV, compared to the polymer P(SeT2) (2.27 eV). Their electrochromic performances displayed that P(SeT2) had a higher optical contrast (46.2%) and a lower response time (oxidation time of 1.34 s at 680 nm). The first electrochemically-synthesized poly(selenophenothiophene) films showed good electrochemical activity and electrochromic properties. Moreover, this pioneering study suggests a new strategy for designing and preparing organic electrochromic materials possessing selenophenothiophene units.

Verification of corrosion inhibition of Mild steel by some 4-Aminoantipyrine-based Schiff bases – Impact of adsorbate substituent and cross-conjugation

Corrosion inhibition of mild steel (MS) by a series of 4-aminoantipyrine-based Schiff base has been studied in 1 N HCl aqueous medium adopting electrochemical method at different concentration (10-2–10-5 M) and temperature (303–333 K). All of the inhibitors were found to be dominated by cathodic/anodic in nature (mixed type). Electrochemical impedence and polarization studies were in agreement with each other. The surface morphology (smoothness and roughness) was characterized by SEM, which indicates the formation of protective layer on the MS surface. The substituents on the Schiff bases influence their corrosion inhibition properties.Schiff bases having OCH3, OH and NMe2 substituents exhibit more inhibition tendency as compared to other substituents. The role of cross conjugation in electron donating as well as accepting properties by heteroatom (N, O) and π-electrons in corrosion inhibition was clearly observed from DFT calculations. Monolayer formation on the MS surface has been confirmed from the Langmuir isotherm fitting. Thermodynamic modeling has been done to understand the nature of adsorption. The values of ΔG (>−30 kJ/mol/K) indicate the existence of both physical and chemical interactions between the Schiff base molecules and metal surface.

Novel halogenated cyclopentasilylene‐2,4‐dienes via DFT

AbstractIn view of immense importance of silylenes and the fact that their properties undergo significant changes on substitution with halogens, here, we have used B3LYP/6‐311++G** level of theory to access the effects of 1–4 halogens (X = F, Cl, Br, and I) on four unprecedented sets of cyclopentasilylene‐2,4‐dienes; with the following formulas: SiC4H3X (1 X), SiC4H2X2 (2 X), SiC4HX3 (3 X), and SiC4X4 (4 X). In going down from F to I, the singlet (s)‐triplet (t) energy gap (ΔEs‐t, a possible indication of stability), and band gap (ΔEH‐L) decrease while nucleophilicity (N), chemical potential (μ), and proton affinity (PA) increase. The overall order of N, μ, and PA for each X is 2 X > 1 X > 3 X > 4 X. Precedence of 2 X over 1 X is attributed to the symmetric cross conjugation in the former. The highest and lowest N are shown by 2 I and 4 F. The trend of divalent angle () for each X is 4 X > 1 X > 3 X > 2 X. The results show that in going from electron withdrawing groups (EWGs) to electron donating groups (EDGs), the ΔEs‐t and ΔEH‐L decrease while N, μ, and PA increase. Also, rather high N of our scrutinized silylenes may suggest new promising ligands in organometallic chemistry.

A spectrophotometric study of impact of solvent, substituent and cross-conjugation in some 4-aminoantipyrine based Schiff bases.

The influences of substituent and solvent polarity on the electronic transition of seven different 4-aminoantipyrine based Schiff bases have been investigated in 14 solvents of different polarity. Reichardt'sET(30) scale has been used to propose a quantitative approach towards the relative stability of the electronic ground and excited state species. The Schiff bases can sense the polarity changes of the solvents and accordingly there appear three categories of solvents: non-polar, dipolar aprotic and polar protic. The first two categories of solvents induce negative solvatochromism and the third one induces positive solvatochromism in the molecules. Cross conjugation and geometrical configuration have been proposed to play an important role in the extent of electronic transition of the Schiff bases in various solvent media. Out of various substituent effects, field effect and resonance significantly influence the electronic environment of the compounds, as evidenced from the regression models involving change in UV-Vis absorption wavelengths 1HNMR chemical shifts and IR frequencies.

The synthesis of a hexameric expanded hemiporphyrazine

Although the chemistry of expanded porphyrins is well developed, there has been significantly less work on expanded isoindoline based macrocycles such as hemiporphyrazines. In this report we present the synthesis and characterization of a new hexameric expanded hemiporphyrazine which we refer to as hexahemiporphyrazine. The synthesis incorporated bis(6-amino-2-pyridyl)amine as a starting material, which could be produced from 2,6-diaminopyridine using melt reaction conditions. Bis(6-amino-2-pyridyl)amine can adopt a three different conformations, two of which are observed in the free base and protonated form, and the third in the backbone of hexahemiporphyrazine. Reaction of bis(6-amino-2-pyridyl)amine and diiminoisoindoline in the presence of a catalytic amount of BF3 produces the hexihemiporphyrazine macrocycle, which was characterized spectroscopically and by X-ray crystallography. Structure elucidation reveals two inverted pyridine rings in a configuration reminiscent of that seen in hexaphyrin, however hexahemiporphyrazine lacks cross conjugation across the macrocycle.

Cross Conjugation in Polyenes and Related Hydrocarbons: What Can Be Learned from Valence Bond Theory about Single-Molecule Conductance?

This study examined the nature of the electronic structure of representative cross-conjugated polyenes from a valence bond (VB) perspective. Our VBSCF calculations on a prototypical dendralene model reveal a remarkable inhibition of the delocalization compared to linear polyenes. Especially along the C-C backbone, the delocalization is virtually quenched so that these compounds can essentially be considered as sets of isolated butadiene units. In direct contrast to the dendralene chains, quinodimethane compounds exhibit an enhancement in their delocalization compared to linear polyenes. We demonstrate that this quenching/enhancement of the delocalization is inherently connected to the relative weights of specific types of long-bond VB structures. From our ab initio treatment, many localization/delocalization-related concepts and phenomena, central to both organic chemistry and single-molecule electronics, emerge. Not only do we find direct insight into the relation between topology and the occurrence of quantum interference (QI), but we also find a phenomenological justification of the recently proposed diradical character-based rule for the estimation of the magnitude of molecular conductance. Generally, our results can be conceptualized using the "arrow-pushing" concept, originating from resonance theory.

The impact of heteroatom substitution on cross-conjugation and its effect on the photovoltaic performance of DSSCs - a computational investigation of linear vs. cross-conjugated anchoring units.

The unusual bonding pattern and proximal heteroatom substitution in π-cross conjugation produced distinct changes in the energy levels and photophysical behaviour of the dyes. To seek an understanding of the origin of these fluctuations, we have carried out a detailed computational investigation on a series of D-π1-π2 (A1)-A2 structured dyes comprised of common donor-spacer (auxiliary acceptor) units but varied the anchoring parts. In this study, we introduced a novel dimethylamino substituted fluorene-based triarylamine donor unit and evaluated its donating strength. Based on the comparison of DFT computed energy levels with experimental results, we have proposed an orbital splitting pattern to explain the energy level and photophysical properties of the linear vs. cross-conjugated dyes with respect to the linking position of the anchoring unit and benzo[1,2,5]thiadiazole (BTD) substitution. The smallest HOMO-LUMO gap of B3 mainly originated from the weak overlap of the directionality mismatch of the orbital interaction imposed by cross-conjugation. The inefficient overlap in B3 can possibly influence the energy levels but failed to enhance the charge transfer transitions upon photoexcitation. On the other hand, β-heteroatom substitution in bridged dyes partially enhanced π-delocalization over the cross conjugation and produced a significant ICT absorption with an optoelectronic response in the NIR region. BTD acceptor substitution increased the HOMO-LUMO gap of the bridged dyes. NBO analysis was performed to corroborate our predictions. DOS-PDOS analysis of the dyes@TiO2 was employed to investigate the electron injection rate of linear vs. bridged dyes. The anchoring pattern and large torsional deviation of the carboxylate anchoring group upon TiO2 adsorption drastically decreased the photovoltaic performance of the bridged dyes. The results obtained from this study provided a detailed understanding of how to surmount the cross-conjugation with the aid of β-heteroatom substitution. These design guidelines would be helpful in developing novel NIR dyes with better hole mobility for various optoelectronic applications. Furthermore, π-delocalization over the cross-conjugation concept opens a new pathway in the field of functional molecular devices to increase the charge conductance over several orders of magnitude with a significant reduction of destructive quantum interference at the molecular junction.

2-[4-(Dimethylamino)phenyl]-3,3-difluoro-3H-naphtho[1,2-e][1,3,2]oxazaborinin-2-ium-3-uide

In the title compound, C19H17BF2N2O, a twist about the N—C single bond is observed, making the cross conjugation not as efficient as in the case of a planar structure. The borone complex has tetrahedral geometry. In the crystal, molecules are conected by weak C—H...F hydrogen bonds.

Cross-Conjugated [36]Octaphyrins

Cross-Conjugated [36]Octaphyrins

Cross Conjugation. Modern Dendralene, Radialene and Fulvene Chemistry. Edited by Henning Hopf and Michael S. Sherburn.

Cross Conjugation. Modern Dendralene, Radialene and Fulvene Chemistry. Edited by Henning Hopf and Michael S. Sherburn.

A naphthalene-fused dimer of an anti-aromatic expanded isophlorin.

We report the first synthesis of a covalent expanded isophlorin dimer from two 24-π doubly S-confused sapphyrin-like pentathiaisophlorins. It exhibits marginal peripheral aromaticity rather than strong global diatropicity or paratropicity and weak intermacrocycle electronic communication. Quantum chemical methods discern that cross-conjugation is responsible for these unusual electronic features.

交差共役系での置換基効果

交差共役系での置換基効果

Electrochemical control of single-molecule conductance by Fermi-level tuning and conjugation switching.

Controlling charge transport through a single molecule connected to metallic electrodes remains one of the most fundamental challenges of nanoelectronics. Here we use electrochemical gating to reversibly tune the conductance of two different organic molecules, both containing anthraquinone (AQ) centers, over >1 order of magnitude. For electrode potentials outside the redox-active region, the effect of the gate is simply to shift the molecular energy levels relative to the metal Fermi level. At the redox potential, the conductance changes abruptly as the AQ unit is oxidized/reduced with an accompanying change in the conjugation pattern between linear and cross conjugation. The most significant change in conductance is observed when the electron pathway connecting the two electrodes is via the AQ unit. This is consistent with the expected occurrence of destructive quantum interference in that case. The experimental results are supported by an excellent agreement with ab initio transport calculations.