Vinylene Bridge Research Articles

Push-pull chromophores with π-deficient benzoazine and π-excessive thiophene cores in conjugated bridge as sources of quadratic nonlinear optical activity of composite polymer materials and molecular glasses

Impact of π-deficient heterocyclic core (A′) in conjugated bridge of D-π-A′-π-A chromophores (D = N,N-dihexylaniline, A = tricyanofuran derivative) on optical and thermal properties has been investigated. Three new chromophores with vinyl-hetaryl-vinyl bridges containing π-deficient benzoazine moiety (quinoxaline, quinoxalinone and quinoline) have been synthesized along with new chromophores with vinyl-thiophene-vinyl bridge containing π-excessive heterocycle and short vinylene bridge, and their properties are compared to reveal the role of π-deficient hetaryl moiety. Their linear optical properties were systematically investigated by UV–Vis spectroscopy and molecular nonlinear optical (NLO) characteristics were predicted by DFT calculations. As the aromaticity of the heterocycle in the bridge increases, a hypochromicity and hypsochromic shift of the absorption maximum manifest themselves in the UV–Vis spectra, the origin of electron transitions was studied by TD-DFT with CAM-B3LYP and PBE0 density functionals. The calculated first hyperpolarizability, βtot, for A′ = quinoxaline, quinoline and thiophene, was shown to be almost independent on the type of the π-bridge core, being in a narrow interval 800–831⋅10−30 esu, while for A′ = quinoxalinone βtot is essentially higher (996⋅10−30 esu). All chromophores exhibit good thermal stability (Td > 192 °C). Thin films of composite polymer materials with PMMA matrix and studied chromophores as guests as well as of some molecular glasses were spin-cast and corona-poled, and their quadratic NLO activity was measured by two different techniques. For materials with guest chromophores containing quinoxalinone, quinoxaline and thiophene moieties in the bridges NLO coefficients d33 were found to be rather close and reached 76 pm/V, what is almost 3 times higher than that for polymer film with quinoline-based chromophore. Rather high values of NLO coefficients for molecular glasses based on chromophores with quinoline, thiophene and quinoxalinone cores were obtained: 52, 124 and 132 pm/V, respectively, which notably exceed the values for composite materials with these chromophores as guests.

Synthesis, characterization, antibacterial activity, and molecular docking of novel dicyanodihydrofuran-based push-pull fluorophores.

Novel push-pull fluorescent molecules based on dicyanodihydrofuran that had marked molar extinction coefficients were created and described. The fluorophores were synthesized using the Knoevenagel condensation in arid pyridine at room temperature and acetic acid as a catalytic agent. In addition, a condensation reaction was performed for the activated methyl-containing dicyanodihydrofuran with a 3° amine-containing aromatic aldehyde. The molecular structures for the synthesized fluorophores were determined using various spectral techniques such as 1 H or 13 C nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, and C, H, N analysis. Ultraviolet-visible (UV-vis) absorption and emission spectra of the prepared fluorophores revealed a high extinction coefficient, which was monitored to be affected by the type of the aryl (phenyl and thiophene)-vinyl bridge in conjugation with the 3° amine donor moiety. The substituents bonded to the tertiary amine, aryl, and alkyl groups, were found to affect the maximum absorbance wavelength. In addition, the synthesized dicyanodihydrofuran analogues were investigated to determine their antimicrobial effectiveness. Derivatives 2b, 4a, and 4b showed reasonable activity towards Gram-positive(+ve) bacteria rather than Gram-negative(-ve) bacteria relative to an amoxicillin drug reference. In addition, a molecular docking stimulation was performed to explore the binding interactions (PDB code: 1LNZ).

The role of acceptor and π-bridge for donor-driven halochromism of D-π-A N,N-dialkylaminostyrylhetarenes

The photophysical properties of a series of D-π-A chromophores, where D is represented by di- or trialkylaniline moiety, π – vinylene, A - quinoxaline, quinoxalinone, quinoline, benzothiazole and thiophenecarboxaldehyde, have been analyzed upon acidification. In all cases, appearance of the second emission band is associated with protonation of the nitrogen atom in the donor fragment. Nevertheless, the simultaneous appearance of two emission bands at equal amounts of acid is observed only for dyes with a quinoxalinone acceptor fragment, which suggests the crucial role of the latter in providing dual emission upon acidification. The highest pH sensitivity has been achieved for the dye with an ethyl group at the ortho-position of benzene ring relative to the vinylene bridge. In contrast, the variation of substituents at the aniline nitrogen atom, the protonation of which causes the appearance of the emission under acidic conditions, does not lead to significant changes in pH sensitivity.

Phenalene—A New Ring-Locked Vinyl Bridge for Nonfullerene Acceptors With Enhanced Chemical and Photochemical Stabilities

Currently, the two exocyclic vinyl bridges in the acceptor–donor–acceptor (A–D–A)-type nonfullerene acceptors (NFAs) have been widely recognized as one of the most vulnerable sites under external stresses. Embedding the exocyclic vinyl bridges into an aromatic ring could be a feasible solution to stabilize them. Herein, we successfully develop a phenalene-locked vinyl bridge via a titanium tetrachloride—pyridine catalytic Knoevenagel condensation, to synthesize two new A–D–A-type unfused NFAs, EH-FPCN and O-CPCN, wherein malononitrile is used as the electron-deficient terminal group while fluorene and carbazole rings are used as the electron-rich cores, respectively. These two NFAs possess wide bandgaps associated with deep energy levels, and significantly enhanced chemical and photochemical stabilities compared to the analogue molecule O-CzCN with normal exocyclic vinyl bridges. When pairing with a narrow bandgap polymer donor PTB7-Th, the fabricated EH-FPCN- and O-CPCN-based organic solar cells achieved power conversion efficiencies of 0.91 and 1.62%, respectively. The higher efficiencies for O-CPCN is attributed to its better film morphology and higher electron mobility in the blend film. Overall, this work provides a new design strategy to stabilize the vulnerable vinyl bridges of A–D–A-type NFAs.

Acetylene/Vinylene-Bridged π-Conjugated Covalent Triazine Polymers for Photocatalytic Aerobic Oxidation Reactions under Visible Light Irradiation.

Solar-driven photocatalytic chemical transformation provides a sustainable strategy to produce valuable feedstock, but designing photocatalysts with high efficiency remains challenging. Herein, two acetylene- or vinylene-bridged π-conjugated covalent triazine polymers, A-CTP-DPA and V-CTP-DPE, were successfully fabricated toward metal-free photocatalytic oxidation under visible light irradiation. Compared to the one without acetylene or vinylene bridge, both resulting polymers exhibited superior activity in photocatalytic selective oxidation of sulfides and oxidative coupling of amines; in particular, A-CTP-DPA delivered an optimal photocatalytic performance. The superior activity was attributed to the broadened spectral response range, effective separation, rapid transportation of photogenerated charge carriers, and abundant active sites for photogenerated electrons due to the existence of the acetylene bridge in the framework. This work highlights the potential of acetylene and vinylene bridges in tuning catalytic efficiency of organic semiconductors, providing a guideline for the design of efficient photocatalysts.

Emerging Chemistry in Enhancing the Chemical and Photochemical Stabilities of Fused‐Ring Electron Acceptors in Organic Solar Cells

AbstractThe power conversion efficiency of organic solar cells (OSCs) has made exceptionally rapid progress in the past five years owing to the emergence of fused‐ring electron acceptors (FREAs). To achieve the commercialization, it is urgent to resolve the stability issues of OCSs from materials to devices. In particular, the state‐of‐the‐art FREAs, often synthesized by Knoevenagel condensation, generally contain two exocyclic vinyl groups (CC bond) as the conjugated bridges, which inevitably exhibit an obvious electron‐deficient characteristic due to the strong push‐pull electronic effect. As a result, these vinyl bridges are vulnerable to nucleophile attacking and/or photooxidation, leading to poor chemical and photochemical stabilities of FREAs that easily cause the degradation of device performance. In this perspective, an in‐depth understanding of the degradation mechanism of FREAs is provided, and then effective strategies reported recently are reviewed for improving the chemical and photochemical stabilities of FREAs from interfacial engineering to molecular engineering to additive engineering. Finally, a conclusion and outlook for the future design of highly efficient and stable FREAs are also presented.

Substituent Effect on Structures of Hexaphyrins(2.1.2.1.2.1) and Their Metal Complexes

Porphyrins are key materials in nature, as well as having applications as dyes, catalysts, or electron donors and acceptors, among others. Compared with common porphyrins, porphyrins containing vinylene bridges have been less studied, but they have unique properties, such as lower symmetry, flexibility of their frameworks, and cis/trans-isomerization reaction. The symmetry of the porphyrin framework is strongly related to the optical/electronic properties of porphyrins and the flexibility of the framework is related to the switching of aromaticities and coordination to metal ions [1].Hexaphyrins and larger expanded porphyrins consisting of six or more pyrrole rings are significant research targets owing to their large and flexible structures, their optical and electrochemical properties, and their diverse coordination abilities. Although hexaphyrins(1.1.1.1.1.1) have been reported by several groups, hexaphyrins with ethylene bridges have been less frequently reported, because of the limitation of synthetic methods. However, the incorporation of double bonds within porphyrin frameworks markedly affects their molecular structures because cis- and trans-isomers produce different geometries.To synthesize expanded porphyrins incorporating vinylene bridges, we focused on 1,2-di(pyrrol-2-yl)ethene (DPE) derivatives. We found that treatments of trans-DPE with pentafluorobenzaldehyde under acidic conditions selectively gave the [30]hexaphyrin(2.1.2.1.2.1) 1 [2]. In particular, protonated 13+ forms a highly planar structure with strong 30p-electron aromaticity. The free base 1 can be converted into the trinuclear rhodium(I) complex Rh-1. Planar 1 and Rh-1 display a sharp intense Soret-like band and a weak Q-like band in the visible and near infrared (NIR) region, respectively, as a result of their aromatic characteristics.Treatment of phenyl-substituted DPEs (trans- and cis-Ph-DPE) with pentafluorobenzaldehyde in the presence of BF3·OEt2, followed by oxidation with DDQ, gave three expanded porphyrins: the cis,cis-porphyrin(2.1.2.1) 2, the cis,trans,trans-hexaphyrin(2.1.2.1.2.1) 3, and the all-trans-octaphyrin(2.1.2.1.2.1.2.1) 4 [3]. These expanded porphyrins have highly distorted structures, as revealed by X-ray crystallography. Reflecting their structures, these expanded porphyrins exhibit nonaromatic properties.By treatment of hexaphyrin 3 with Zn(OAc)2, Zn-3 was obtained in 83% yield. The Zn-3 is categorized as a nonaromatic compound because of its non-planar structure. Treatment of hexaphyrin 3 with Cu(OAc)2 in CHCl3– MeOH gave Cu-3 in 50% yield, whereas in MeOH, Cu2-3 was obtained in 30% yield. Interestingly, the second copper ion (Cu+) of Cu2-3 is coordinated to the remaining two nitrogen atoms on the dipyrrin unit and to the pyrrolic sp 2 carbons in an η2-coordination manner. Additionally, the molecular structures are drastically changed from the distorted structure of 3 to the figure-of-eight structures of Cu-3 and Cu2-3. This structural change induces a change in electronic properties from the nonaromatic property of hexaphyrin 3 to the aromatic properties of the copper complexes.In this presentation, we will discuss the single crystal structures as well as the optical properties of hexaphyrins(2.1.2.1.2.1) and their metal complexes.

Molecular designing of triphenylamine-based hole-transporting materials for perovskite solar cells

To maximize the performance of perovskite solar cells (PSCs), controlling the hole mobility is of fundamental importance. In this regard, developing efficient hole transport materials (HTMs)is highly desirable in next-generation solar cells. Herein, several dopant-free HTMs, with the donor–acceptor-donor (D-A-D) architecture, are designed based on benzophenone and di (pyridine-3-yl) methanone as the acceptors and triphenylamine (TPA) as the donor. The correlation between electronic structure and hole transport property of the TPA-based HTMs were systematically investigated by tuning the connection between donor and acceptor (single vs. double bond) and also the substitution position of the methoxy groups (ortho, meta, and para). Our results from density functional theory calculations indicate that introducing the vinyl group as the connecting π-bridge can effectively increase the hole mobilities of the designed HTMs. Among the investigated compounds, the combination of benzophenone core acceptor with para-methoxy TPA terminals via the vinyl bridge, called p-TEBET, shows the most promising features and achieves excellent hole mobility (1.58 × 10-1 cm2 V−1 s−1) which is larger than that of spiro-OMeTAD as the most commonly used HTM. The results of the present computational study can be further employed in the process of synthesizing new HTMs with promising features in terms of proper energy alignment, stability, and hole mobility.

Deciphering Benzene–Heterocycle Stacking Interaction Impact on the Electronic Structures and Photophysical Properties of Tetraphenylethene-Cored Foldamers

Deciphering Benzene–Heterocycle Stacking Interaction Impact on the Electronic Structures and Photophysical Properties of Tetraphenylethene-Cored Foldamers

Design of Thienothiophene-Based Copolymers with Various Side Chain-End Groups for Efficient Polymer Solar Cells.

Three two-dimensional donor–acceptor conjugated copolymers consisting of a benzo[1,2-b:4,5-b′]dithiophene derivative and thieno[3,2-b]thiophene with a conjugated side chain were designed and synthesized for use in bulk heterojunction (BHJ) or nonfullerene polymer solar cells (PSCs). Through attaching various acceptor end groups to the conjugated side chain on the thieno[3,2-b]thiophene moiety, the electronic, photophysical, and morphological properties of these copolymers were significantly affected. It was found that the intermolecular charge transfer interactions were enhanced with the increase in the acceptor strength on the thieno[3,2-b]thiophene moiety. Moreover, a better microphase separation was obtained in the copolymer: PC71BM or ITIC blend films when a strong acceptor end group on the thieno[3,2-b]thiophene moiety was used. As a result, BHJ PSCs based on copolymer:PC71BM blend films as active layers exhibited power conversion efficiencies from 2.82% to 4.41%, while those of nonfullerene copolymer:ITIC-based inverted PSCs ranged from 6.09% to 7.25%. These results indicate the side-chain engineering on the end groups of thieno[3,2-b]thiophene unit through a vinyl bridge linkage is an effective way to adjust the photophysical properties of polymers and morphology of blend films, and also have a significant influence on devices performance.

Porphyrinoids with Vinylene Bridges

AbstractPorphyrinoids containing vinylene bridges, such as triphyrin(2.1.1), porphycene, porphyrin(2.1.2.1), and hexaphyrin(2.1.2.1.2.1), are a relatively new family of porphyrinoids. Vinylene bridges give porphyrinoids a lower symmetry and a flexibility of the framework and they permit cis/trans-isomerization reactions; these factors confer unique properties to these substances, such as coordination to metal ions and aromaticity switching. In this account, the synthesis, crystal structures, and properties of new porphyrinoids containing vinylene bridges are summarized.1 Introduction2 Triphyrin(2.1.1)3 Porphycene4 Porphyrin(2.1.2.1)5 Hexaphyrin(2.1.2.1.2.1)6 Conclusion

Vinylene-Bridged Cyclic Dipyrrin and BODIPY Trimers.

Vinylene-bridged cyclic boron–difluoride complex of dipyrrin (BODIPY) trimers were successfully prepared from expanded dimethyl-vinylene bridged hexaphyrin(2.1.2.1.2.1) Me-Hex that has the structure of alternate dipyrrins and vinylene bridges. The hexaphyrin(2.1.2.1.2.1) Me-Hex can coordinate with boron ions to afford five kinds of cyclic BODIPYs given by step-by-step boron complexations. Crystal structures of all cyclic BODIPYs except for 3BF2-Me-Hex(b) formed non-planar structures. The theoretical calculation predicted that mono-/bis-boron cyclic BODIPYs show the intramolecular charge transfer (ICT) characteristics, whereas tri-boron cyclic BODIPYs have no ICT characteristics. Reflecting these electronic properties, tri-boron cyclic BODIPYs exhibit weak fluorescence in the red region, but mono-/bis-boron cyclic BODIPYs exhibit no emission. Vinylene bridged cyclic dipyrrin trimer Me-Hex is the novel porphyrinoid ligand allowed to control the boron coordination under different reaction conditions to form various boron complexes.

Naphthalene diimide based near-infrared luminogens with aggregation-induced emission characteristics for biological imaging and high mobility ambipolar transistors

Organic conjugated materials combining high conductivity with strong solid-state emission are highly desired for organic electronic applications, yet still rather rare. Herein, a novel luminogen (TEN) comprised by linking naphthalene diimides and tri-phenyl ethylene with vinyl bridges is reported. TEN exhibits aggregation-induced emission (AIE) behavior of a strong near-infrared fluorescence over 700 nm and the efficiency above 60.5% in the solid state, while also shows promising application in vivo bio-imaging with good permeability and extremely low background. Single crystal of TEN reveals intra- and inter-molecular C–H···O hydrogen bonds, contributing to an inclined molecular stacking along the a -axis of the cell, creating a 1D charge carrier transporting channel under a short π-π interaction distance of 3.42 A, which might benefit the solid emission and charge transport ability simultaneously. Solution processed bottom contact, top gate organic field effect transistors based on TEN reveal a high ambipolar charge transport ability with the hole mobility up to 0.13 cm2 V−1 s−1 and electron mobility up to 0.010 cm2 V−1 s−1. Further atomic force microscopy and X-ray diffraction analysis on TEN thin film confirm the existence of the 1D π-π stacking channel, suggesting the stacking geometry revealed in crystal crucial for facilitating high charge carrier mobility while preserving the strong solid emission at the same time.

A Vinylene-Bridged Conjugated Covalent Triazine Polymer as a Visible-Light-Active Photocatalyst for Degradation of Methylene Blue.

The development of new photocatalytic platforms using novel semiconductor material is an important challenge. Herein, a sp2 carbon-conjugated covalent triazine polymer (sp2 c-CTP-4), featuring a vinylene bridge and extended π-conjugation, is prepared as a highly efficient photocatalyst for degradation of methylene blue. sp2 c-CTP-4 exhibits substantial semiconducting properties such as enhanced charge transfer and prolonged lifetime of carriers compared to its counterparts with CN or CC connections, likely due to its extended π-delocalization with an unencumbered CC bridge. Moreover, benefiting from its high chemical stability, the as-made catalyst can be recycled five times with good retention of photocatalytic activity. This study provides a new pathway for constructing a robust platform for efficient photocatalysis and gives insight into the structure-property relationship of conjugated polymers.

Achieving Efficient Multichannel Conductance in Through‐Space Conjugated Single‐Molecule Parallel Circuits

AbstractConstructing single‐molecule parallel circuits with multiple conduction channels is an effective strategy to improve the conductance of a single molecular junction, but rarely reported. We present a novel through‐space conjugated single‐molecule parallel circuit (f‐4Ph‐4SMe) comprised of a pair of closely parallelly aligned p‐quaterphenyl chains tethered by a vinyl bridge and end‐capped with four SMe anchoring groups. Scanning‐tunneling‐microscopy‐based break junction (STM‐BJ) and transmission calculations demonstrate that f‐4Ph‐4SMe holds multiple conductance states owing to different contact configurations. When four SMe groups are in contact with two electrodes at the same time, the through‐bond and through‐space conduction channels work synergistically, resulting in a conductance much larger than those of analogous molecules with two SMe groups or the sum of two p‐quaterphenyl chains. The system is an ideal model for understanding electron transport through parallel π‐stacked molecular systems and may serve as a key component for integrated molecular circuits with controllable conductance.

Achieving Efficient Multichannel Conductance in Through-Space Conjugated Single-Molecule Parallel Circuits.

Constructing single-molecule parallel circuits with multiple conduction channels is an effective strategy to improve the conductance of a single molecular junction, but rarely reported. We present a novel through-space conjugated single-molecule parallel circuit (f-4Ph-4SMe) comprised of a pair of closely parallelly aligned p-quaterphenyl chains tethered by a vinyl bridge and end-capped with four SMe anchoring groups. Scanning-tunneling-microscopy-based break junction (STM-BJ) and transmission calculations demonstrate that f-4Ph-4SMe holds multiple conductance states owing to different contact configurations. When four SMe groups are in contact with two electrodes at the same time, the through-bond and through-space conduction channels work synergistically, resulting in a conductance much larger than those of analogous molecules with two SMe groups or the sum of two p-quaterphenyl chains. The system is an ideal model for understanding electron transport through parallel π-stacked molecular systems and may serve as a key component for integrated molecular circuits with controllable conductance.

Orientation Order of Nonelectrically Poled FTC-Type Chromophores in PMMA on SiO2 Surfaces

Abstract We present the orientation order of push-pull chromophores consisting of phenyl vinylene thiophene vinylene (FTC) bridges between the N,-N-bis-(2-hydroxyethyl)-amine electron donor and phenyl-trifluoromethyl-tricyanofuran (TCF-Ph-CF3) acceptor in poly (methyl methacrylate) (PMMA). The chromophores have attracted great attention as a guest material for nonlinear optical polymers for near-IR applications. Our experimental results demonstrated that the chromophores with relatively large molecular weights were oriented in a polar order with the aid of adsorption onto the surfaces of the SiO2 substrates, even without the conventional electrical poling procedure. The polar order of the chromophores extended approximately 50 nm vertically from the substrate surfaces. Polarized linear absorption and second harmonic generation spectroscopies were performed to determine the orientation distribution function of the chromophores in the PMMA. The average molecular tilt angle Θ, indicating the degree of the orientation order, was wider than the magic angle, and the chromophores were preferably oriented horizontally to the substrate surfaces. A relatively low orientation order was explained in terms of the strong dipole-dipole repulsions among the neighboring guest chromophores.

Control of Aromaticity and cis-/trans-Isomeric Structure of Non-Planar Hexaphyrin(2.1.2.1.2.1) and Metal Complexes.

Vinylene-bridged hexaphyrin(2.1.2.1.2.1) was synthesized from dipyrrolyl diphenylethenes by acid-catalyzed condensation reactions. Freebase hexaphyrin(2.1.2.1.2.1) forms a distorted structure with non-aromatic characteristics. The aromaticity and molecular configuration of non-planar hexaphyrin(2.1.2.1.2.1) can be controlled by insertion of metal ions. Freebase and zinc complexes show a distorted structure without macrocyclic aromaticity, whereas copper complexes show a figure-of-eight structure with macrocyclic aromaticity. It is the first example of aromaticity conversion of a distorted expanded porphyrin involving vinylene bridges.

New functional benzo[ghi]perylene derivatives: Synthesis and photophysical properties

New benzo[ghi]perylene derivatives bearing valuable functional groups at well defined positions were synthesized in two steps, in 59%–72% over all yields, using vinyl bridges as precursors. These π-conjugated hexacyclic frameworks have been characterized experimentally using UV-vis absorption and photoluminescence spectroscopies and an emission in the visible region was identified. After characterization by cyclic voltammetry, all derivatives showed electrochemical band gap (Eg-el) less than 2.35 eV indicating that they might be suitable candidates for electron-injection hole-blocking layers.

Novel group of negative photochromes containing a nitrile-rich acceptor: synthesis and photochromic properties

An approach to the synthesis of novel group of negative photochromes has been developed based on the interaction of the tricycanofuran TCF or hydroxytricyanopyrrole HTCP acceptors with methoxy-substituted 2-hydroxybenzaldehydes in ethanol in the presence of ammonium acetate. An essential part of the obtained photochromes is a combination of a phenol fragment and a butadienetricarbonitrile BDTC acceptor connected via a vinylene bridge. The synthesized compounds are sensitive to visible light T-type photochromes. A transformation degree of the initial form, as well as the rate of the reverse dark reaction, can be varied by changing both the position of a methoxy group at aromatic ring and the type of the heterocycle with the BDTC fragment.