Π-conjugated Organic Systems Research Articles

Frustrated π-stacking.

The properties of functional materials based on organic π-conjugated systems are governed extensively by intermolecular interactions between π-molecules. To establish clear relationships between supramolecular structures and functional properties, it is essential to attain structurally well-defined π-stacks, particularly in solution, as this enables the collection of valuable spectroscopic data. However, precise control and fine-tuning of π-stacks pose significant challenges due to the weak and bidirectional nature of π-π stacking interactions. This article introduces the concept of "frustrated π-stacking," strategically balancing attractive (π-π interaction) and repulsive (steric hindrance) forces in self-assembly to exert control over the sizes, sequences of π-stacks, and slip-stacked structures. These research efforts contribute to a deeper understanding of the correlation between π-stacks and their properties, thereby providing useful insights for the development of molecular materials with the desired performance.

Conducting 2D Nanosheets: Photo Driven Crystallinity in Self-Assembled Cu (II) Metalated Porphyrin-Bispyridylquinoxaline

Tuning the crystallinity in self-assembled nanostructures has a significant impact on the electronic properties. Although several approaches have been adopted for organic π-conjugated systems to generate the amorphous to crystalline structures, the bulky structure of extended macrocyclics is hitherto unknown. Herein, we have developed three symmetric freebase and metallo substituted porphyrin appended bispyridylquinoxalines (PFb-DPQ, PCu-DPQ and PZn-DPQ) in which copper metalated P-DPQ exhibits crystalline phase transitions under light stimuli. Notably, light irradiated P-DPQ derivatives undergo a protonation, demetalation, and anion binding mechanism, resulting in the formation of self-assembled open, closed 0D nanospheres together with 2D nanosheets via methanol vapor diffusion approach. Interestingly, light stimulation regulates the morphology from 0D nanosphere to 2D nanosheets in PCu-DPQ and H+[PCu-DPQ(Cl)]−, which promotes the amorphous to crystalline nature. Consequently, the bulk conductivity of 2D nanosheets exhibits ∼32 mS cm–1, and it is remarkably 102 times higher than 0D nanospheres. Thus, these results promote that the stimuli responsive metallo substituted macrocyclic systems is a significant initiative to manipulate the electronic properties in organic electronics.

Multifunctional broadband visible-light absorbing selenophene modified bodipy photosensitizers

Large π-conjugated organic systems with effective photosensitization are highly desirable for many photochemical applications. Herein, a series of π-conjugated selenophene-substituted boron dipyrromethene (known as bodipy) dyes (MB-Se, 2B–Se, MB-Se-2Br) were prepared by appending selenophene electron-donor to the core of bodipy acceptors via alkynyl bridge and their excited state properties were investigated. Optical spectroscopy revealed that although these three selenophene-substituted bodipy dyes have nearly identical molecular profiles, their photophysical properties and excited state dynamics are drastically different. Higher triplet quantum efficiency (ΦΔ = 82%) was observed for MB-Se, derivative in which α,β-positions of bodipy decorated with methyl substituents, compared to another dye 2B–Se, which showed inefficient triplet population (ΦΔ = 25%). Employing steady-state absorption and emission spectroscopies, we demonstrated that the designed selenophene-substituted bodipy dyes has excellent J-aggregation capabilities. Notably, the J-aggregates of selenophene-substituted bodipy dyes display NIR emission. The potential of devised selenophene-substituted bodipy dyes in triplet fusion upconversion was also demonstrated; a blue upconverted emission was realized upon irradiating the mixture of bodipy dyes and TIPS-AC acceptor with 589 nm CW-laser. The selenophene-substituted bodipy dyes were also confirmed to be a potent photodynamic therapeutic reagent; with an IC50 value of 0.76 μM, nearly 6 times lower than that of the iodide-appended bodipy photosensitizer (BDP-2I, 6.0 μM). This study hopes to provide valuable guidelines for the future development of multipurpose triplet photosensitizers.

基于6,13-双氰基并五苯一维滑移堆积微米带状晶体 的双极性电荷传输

Featuring small charge transport scattering, mesoscale size, and easy fabrication, one-dimensional self-assembled micro/nanomaterials (1D-MNMs) based on organic π-conjugated systems can be facilely incorporated into integrated microcircuits. Although tremendous progress has been made in 1D-MNMs based on p- or n-channel organic semiconductors, examples of lD-MNMs based on ambipolar organic semiconductors are scarce. Herein, we achieved a novel 1D-MNM based on 6,13-dicyanopentacene (DCP) with a 1D slipped stacking motif using the physical vapor transport method. The DCP-based 1D-MNM showed outstanding, well-balanced ambipolar charge transport with electron and hole mobilities of up to 0.34 and 0.38 cm2 V−1 s−1, respectively, which are among the best ambipolar transport characteristics of 1D-MNMs. Furthermore, a complementary inverter based on the ambipolar 1D-MNM of DCP was also constructed with a gain of up to 7, indicating potential application in organic logic circuits.

Facile in situ construction of novel hybrid 3D-BiOCl@PDA heterostructures with vacancy induced charge transfer for efficient visible light driven photocatalysis and antibacterial activity

Combining a wide band BiOCl semiconductor with organic π-conjugated systems is critical for increasing its light absorption and charge carrier mobility at heterojunction interfaces for efficient photocatalysis. In this study, we described a bioinspired dopamine-assisted one-pot route as an environmentally benign method to construct multifunctional in situ hybrid 3D-BiOCl@PDA heterostructure photocatalysts in an aqueous medium under mild conditions. The versatile role of dopamine was utilized for the controlled integration of 3D-BiOCl (001) hierarchical microspheres while simultaneously modified their surfaces with thin layers of PDA via its in situ polymerization. TGA, UVDRS, and XPS revealed that PDA thickness and its cooperative chelating effect with BiOCl nanosheet at a hybrid interface allowed effective charge transfers, and band-edge shift, induced oxygen defects for extended visible light absorptions. The resulting hybrids exhibited evidently multifunctional photocatalytic performance for complete RhB dye removal (12 times), enhanced selective benzyl alcohol oxidation (>99 benzaldehyde) and excellent antibacterial activity against Staphylococcus aureus (99.9%) than bare BiOCl under identical conditions. Furthermore, the hybrids showed excellent photostability and recyclability for up to five reaction cycles. These highly enhanced results are attributed to their 3D-structural features and close contact between PDA and BiOCl. Based on the results of active species experiments and ESR spectral analysis a possible Z-scheme photocatalytic mechanism has been proposed for the hybrid heterostructure system. Hence, the present work is an effective noble metal-free strategy for creating novel hybrid BiOCl heterostructures with multifunctional properties for visible light photocatalytic applications.

Computational modeling for the design of new fluorescent organic compounds based on both diketopyrrolopyrrole and nitrobenzofurazan moieties

• Design of new fluorescent organic compounds based on both diketopyrrolopyrrole and nitrobenzofurazan moieties. • Planar geometry stabilized by intra-molecular non-covalent interactions (NCIs). • Excellent optoelectronic properties of the studied compounds. • Push-pull effects on the geometrical, optical and charge transfer properties of the designed molecules have been examined. • Potential applications of the designed materials for their use in OSCs and NLO devices. Three examples of organic π-conjugated systems, based on both diketopyrrolopyrrole (DPP) and nitrobenzofurazan (NBD) were theoretically designed as host fluorescent materials that all of them emitted intense infrared fluorescence and the maximum emission bands ranged from 841 nm to 868 nm. Theoretical analysis by utilizing density function theory (DFT) and its extension of TD-DFT methods with B3LYP functional at the 6–311 g(d,p) calculation level, in acetonitrile, have been reported on the geometry, optoelectronic, absorption/emission characteristics of the studied materials. The furan-, thiophene-, or selenophene-flanked-DPP and coupled to NBD, named after M1 (X = O), M2 (X = S) and M3 (X = Se), have a great impact on optoelectronic properties to design lower optical band gap materials with excellent nonlinear optical (NLO) properties and efficient intra-molecular charge transfer (ICT). The studied molecular structures adopt a planar geometry stabilized by intra-molecular non-covalent interactions (NCIs). The reduced density gradient (RDG) has been further developed to analyze and understand the typical NCIs and their characteristics. The analysis of electron density and its reduced density gradient (RDG), NCIs, the topological analyses from MEP, ELF and LOL, QTAIM were carried out to evaluate the charge transfer within the investigated compounds.

Investigating structure-charge transport relationships in thiophene substituted naphthyridine crystalline materials by computational model systems.

The development of novel π-conjugated charge transfer mediators is at the forefront of current research efforts and interests. Among the plethora of building blocks, diketopyrrolopyrroles have been widely employed, associated to the ease of tailoring their optoelectronic properties by systematic peripheral substitutions. It is somehow of surprise to us that their six-member ring bis-lactam analogues, naphthyridines have been overlooked and reports are scarce and almost solely limited to their use in polymeric materials. Herein we report a comprehensive theoretical analysis of the charge transfer properties of 1,5-naphthyridine-based materials by means of a number of bespoke model systems, further able to quantitatively predict experimental mobility observations. Our results imply that thiophene substituted naphthyridine crystalline materials represent a promising class of organic π-conjugated systems with an experimentally observed ability to self-assemble in the solid state conforming to one dimensional stacking motifs. These highly sought-after charge propagation channels are characterised by large wavefunction overlap and thermal integrity and have as a result the potential to outperform currently exploited alternatives. We anticipate this work to be of interest to materials scientists and hope it will pave the way towards the realisation of novel charge transfer mediators exploiting naphthyridine chemistries.

Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca2N]+•e- in an Alcoholic Solvent: An Analogue of Solvated Electrons.

Birch reduction of aromatic systems by solvated electrons in alkali metal-ammonia solutions is widely recognized as a key reaction that functionalizes highly stable π-conjugated organic systems. In spite of recent advances in Birch reduction with regard to reducing agent and reaction conditions, there remains an ongoing challenge to develop a simple and efficient Birch reaction under mild conditions. Here, we demonstrate that the inorganic electride [Ca2N]+•e- promotes the Birch reduction of polycyclic aromatic hydrocarbons (PAHs) and naphthalene under alcoholic solvent in the vicinity of room temperature as a solid-type analogy to solvated electrons in alkali metal ammonia solutions. The anionic electrons from electride [Ca2N]+•e- are transferred to PAHs and naphthalene via alcoholysis in a polar cosolvent medium. It is noteworthy that a high conversion yield to the hydrogenated products is ascribed to the extremely high electron transfer efficiency of 98%. This simple protocol utilizing an inorganic electride offers a direct and practical strategy for the reduction of aromatic compounds and provides an outstanding reducing agent for synthetic chemistry.

Copper-Catalyzed Direct, Regioselective Arylamination of N-Oxides: Studies To Access Conjugated π-Systems.

An efficient copper(I)-catalyzed direct regioselective arylamination of various heterocyclic N-oxides was achieved successfully under redox-neutral conditions using anthranils as arylaminating reagents. The developed protocol is simple, straightforward, and economic with a broad range substrate scope. The dual functional groups in the final molecules were utilized to construct structurally and functionally diverse nitrogen-containing organic π-conjugated systems.

Metal-free Oxidative Cross-Coupling Reaction of Aromatic Compounds Containing Heteroatoms

The biaryl unit containing a heteroatom is a key structure in a large number of natural products and π-conjugated organic systems. The cross-couplings can provide powerful methods for the construction of biaryls and heterobiaryls; thus the development of a new coupling method has been intensively studied by synthetic chemists. Therefore, the oxidative biaryl coupling reaction of arenes containing a heteroatom is a significantly attractive, convenient, and straightforward route to the synthesis of biaryls due to its operational simplicity avoiding the preparation of the corresponding halogenated and metallated arenes. In this report, recent progress in the field of metal-free oxidative cross-coupling reactions of aromatic compounds using hypervalent iodine(III) reagents, is presented.1 Introduction2 Cyanation and Halogenation Reactions of Heteroaromatic Compounds3 Biaryl Coupling Reaction of Heteroaromatic Compounds3.1 Regioselective Coupling Reaction of Thiophenes3.2 Cross-Coupling Reaction of Thiophenes3.3 Coupling Reaction of EDOT and Pyrroles3.4 Cross-Coupling Reaction of Pyrroles4 Cross-Coupling Reaction of Anilines5 Cross-Coupling Reaction of Phenols6 Cross-Coupling Reaction of N-Heteroaromatics with Aryl Radicals from Diaryliodonium(III) Salts7 Conclusion

ChemInform Abstract: π‐Conjugated Cyanostilbene‐Based Optoelectric Functional Materials

AbstractReview: [55 refs.

π -Conjugated cyanostilbene-based optoelectric functional materials

π-Conjugated organic luminescent materials are essential components for modern optical and photoelectric research. This review mainly probes into the recent work in the progress of smart π-conjugated organic systems in the form of cyanostilbene and its derivatives, which can regulate its excellent features in response to a variety of physical or chemical stimuli (e.g. viscosity, light, magnetism, electric field, polarity, pH and solvent environment). As a result of its extensive applicability and adaptability, cyanostilbene and its derivatives have been planted into different structural architectures such as polymers, functional nanoparticles, solid membranes, supramolecular systems and so on. This review will first give a general description of the preparation and characterization of cyanostilbene-based optoelectric luminophores and then focus on their peculiar functional properties in the need for advanced material applications, such as AIEE (aggregation-induced enhanced emission effect), solid-state emission, photovoltaics, photolithography and photochromism to be further processed afterwards. The purpose of this review is to give a platform of practical organic materials, mostly cyanostilbene and its derivatives, based on stable aromatic derivatives, to contribute to the booming of modern π-conjugated photoelectric materials that integrate with contemporary physics, material chemistry, bioengineering, medical science and aerospace altogether.

Effect of metal complexation on the nonlinear optical response of a conjugated ligand

Organic nonlinear optical materials are widely investigated materials for fabricating optoelectronic devices. Particularly organic π-conjugated systems as well as transition metal complex compounds are studied in this direction because of the strong electronic coupling between the ligand and the metal, their excellent chemical stability, and their rich photochemical and photophysical properties. In this work, comparative studies of the third-order nonlinear optical susceptibilities of a bipyridine ligand (4-(N,N-dibutylamino)-4′-(5-ethynyl-2,2′-bipyridine)-azobenzene (A) and of the corresponding heteroleptic ruthenium complex (Ru(bpy)2(La)(PF6)2 (B) (La signifies the ligand) are presented. The NLO properties were investigated by means of the Z-scan technique using a 30 ps mode-locked Nd-YVO4 laser at 532 nm with a repetition rate of 10 Hz. Our results show that the introduction of the metal in the organic complex results in a significant modification of the third-order nonlinear optical response.

Electron–phonon coupling and charge-transfer excitations in organic systems from many-body perturbation theory

We review in this article recent developments within the framework of ab initio many-body perturbation theory aiming at providing an accurate description of the electronic and excitonic properties of π-conjugated organic systems currently used in organic photovoltaic cells. In particular, techniques such as the GW and Bethe–Salpeter formalisms are being benchmarked for acenes, fullerenes, porphyrins, phthalocyanines, and other molecules of interest for solar energy applications. It is shown that not only the electronic properties, but also the electron–phonon coupling matrix elements, and the charge-transfer excitations in donor/acceptor complexes, are accurately described. The present calculations on molecules containing up to a hundred atoms are based on a recently developed Gaussian auxiliary basis implementation of the GW and Bethe–Salpeter formalism, including full dynamics with contour-deformation techniques, as implemented in the Fiesta code.

Origin of the Enhancement of the Second Hyperpolarizabilities in Open-Shell Singlet Transition-Metal Systems with Metal–Metal Multiple Bonds

Using the spin-unrestricted coupled-cluster method, we explore the origin of the second hyperpolarizabilities (γ) of singlet dichromium(II) and dimolybdenum(II) model systems with various bond lengths as a function of the diradical characters of the dσ, dπ, and dδ orbitals. Both systems exhibit enhanced γ values in the intermediate diradical character region, but by using a partitioning scheme, the dσ electrons are shown to play the essential role in contrast with the π-electrons of conventional organic π-conjugated systems. Then, in the equilibrium bond length region, the γ values are still governed by dσ electrons in the dichromium(II) system, although by dδ/dπ electrons in the dimolybdenum(II) system.

Molecular electrostatic potential for exploring π-conjugation: a density-functional investigation

Molecular electrostatic potentials (MESP) of the most common building blocks of organic π-conjugated systems, viz. ethylene, acetylene, benzene, furan, pyrrole, thiophene and phenylvinylene, are examined at the B3LYP/6-311++G(2d,2p) level. The topography of MESP is employed for mapping the strength of electronic conjugation between these building blocks. When electron-rich molecular regions are connected to each other, the MESP value of the corresponding conjugation critical point (CCP) is able to provide a quantitative measure of the strength of the conjugation. The systems with stronger conjugation are generally seen to possess a larger negative value of CCP and a smaller difference (ΔV(CM-CCP)) between the MESP values of respective conjugated minimum (CM) and the CCP, in agreement with the experimental as well as other theoretical results. The present MESP topography-based approach thus offers a measure of the quantitative strength of π-conjugation in molecules.

Hybrid nanostructures using π-conjugated polymers and nanoscale metals: synthesis, characteristics, and optoelectronic applications

Pi-conjugated organic systems have been used as optoelectronic and sensing materials due to their characteristics of efficient light emission or absorption, and p-type charge transport. The hybrid nanostructures of pi-conjugated organic systems with nanoscale metals offer surface plasmon (SP)-enhanced luminescence, which can be applied to organic-based optoelectronics, photonics, and sensing. Various hybrid nanostructures using light-emitting polymers with nanoscale metals have been fabricated and have shown considerable enhancement of photoluminescence efficiency due to energy and charge transfer effects in SP resonance coupling. In this tutorial review, recent conceptual and technological achievements in light-emitting polymers-based hybrid nanostructures are described.

π‐Conjugated Systems: Can Phosphole Offer More than Pyrrole?

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Ab Initio MO Analysis of Interaction Paths between Radicals in Ferromagnetic Organic Systems

Interaction path analyses for pi-conjugated organic systems were performed at the ab initio molecular orbital level to examine the relationship between inter-radical interactions and the high-spin stability of the system. It was found that the high-spin stability results from through-bond interactions between radicals, not from through-space interactions, in relation to the stabilization of a low-spin state due to the effects of electron correlation. L(ij)(min) value for estimating the mixing of nonbonding molecular orbitals well predicted the relationship between the through-bond interactions and the high-spin stability. Furthermore, molecular orbital calculations revealed that the all-trans type interaction path between radicals produces long-range exchange interactions, and the additivity of high-spin stability is observed by keeping short-range through-bond interaction paths.

π-Conjugated systems: Can phosphole offer more than pyrrole?

Abstract An overview of the synthesis, physical properties, and use as material for organic light-emitting diodes (OLEDs) of linear organic π-conjugated systems incorporating phosphole and thiophene rings is presented.