Π-conjugated Materials Research Articles

Strong Non-Reciprocal Chiroptical Properties in Thin Films of Chiral Alkylthio-Decorated 1,4-Phenylene/Thiophene Dyes.

In the context of chiral π-conjugated materials, the use of enantiopure alkylthio appendages represents a valid alternative to conventional alkoxy groups: sulphur atom is bigger and more electron-rich than oxygen, thus allowing for higher polarizability, greater flexibility, larger bulkiness and lower structural anisotropy. In light of these considerations, here we report two new chiral alkylthio-decorated 1,4-phenylene/thiophene dyes, obtained by simple synthetic strategies involving Pd-catalyzed cross-coupling protocols, looking for strong non-reciprocal chiroptical features in thin films. In particular, for the chiral alkylthio-decorated 1,4-phenylene-bis(thiophenylpropynone) (Thio-PTPO) dye, which proved to be the most promising for our purpose, a detailed investigation in thin films was carried out, involving optical and chiroptical spectroscopies in absorption and emission, as well as optical microscopy techniques.

Multiple Redox Site π-Conjugated Materials for Aqueous Aluminum–Organic Battery Cathodes

Multiple Redox Site π-Conjugated Materials for Aqueous Aluminum–Organic Battery Cathodes

Modulating the Photophysical Properties of Twisted Donor-Acceptor-Donor π-Conjugated Molecules: Effect of Heteroatoms, Molecular Conformation, and Molecular Topology.

ConspectusModulating the photophysical properties of organic emitters through molecular design is a fundamental endeavor in materials science. A critical aspect of this process is the control of the excited-state energy, which is essential for the development of triplet exciton-harvesting organic emitters, such as those with thermally activated delayed fluorescence and room-temperature phosphorescence. These emitters are pivotal for developing highly efficient organic light-emitting diodes and bioimaging probes. A particularly promising class of these emitters consists of twisted donor-acceptor organic π-conjugated scaffolds. These structures facilitate a spatial separation of the frontier molecular orbitals, which is crucial for achieving a narrow singlet-triplet energy gap. This narrow gap is necessary to overcome the endothermic reverse intersystem crossing process, enhancing the efficiency of thermally activated delayed fluorescence. To precisely modulate the photophysical properties of these emitting materials, it is essential to understand the electronic structures of new donor-acceptor scaffolds, especially those influenced by heteroatoms, as well as their conformations and topologies. This understanding not only improves the efficiency of these emitters but also expands their potential applications in advance technologies.In 2014, the Takeda group made a significant breakthrough by discovering a novel method for synthesizing U-shaped diazaacenes (dibenzo[a,j]phenazine) through an oxidative skeletal rearrangement of 1,1'-binaphthalene-2,2'-diamines. This class of compounds is typically challenging to synthesize using conventional organic reactions. The resulting unique geometric and electronic structure of U-shaped diazaacenes opened new possibilities for photophysical applications. Leveraging the U-shaped structure, photoluminescent properties, and high electron affinity, we developed twisted donor-acceptor-donor compounds. These compounds exhibit efficient thermally activated delayed fluorescence, stimuli-responsive luminochromism, heavy atom-free room-temperature phosphorescence, and anion-responsive red shifts. These innovative emitters have demonstrated significant potential in various practical applications, including organic light-emitting diode devices and advanced sensing systems.In this Account, I summarize our achievements in modulating the photofunctions of dibenzo[a,j]phenazine-cored twisted donor-acceptor-donor compounds by controlling excited-state singlet-triplet energy gaps through conformational regulation. Our comprehensive studies revealed the significant impact of heteroatoms, molecular conformations, and topologies on the photophysics of these compounds. These findings highlight the importance of molecular engineering in tailoring the photophysical properties of organic donor-acceptor π-conjugated materials for specific applications. Our research has demonstrated that incorporating heteroatoms into the molecular framework effectively tunes the electronic properties and, consequently, the photophysical behavior of the compounds. Understanding the influence of heteroatoms, conformational dynamics, and molecular topology on excited-state behavior will open new avenues for next-generation optoelectronic devices and biological technologies. These advancements include ultra-low-power displays, photonic communication, and super-resolution biomedical imaging. Ultimately, our work highlights the potential of strategic molecular design in driving innovation across various fields, paving the way for the development of cutting-edge technologies that leverage the unique properties of organic emitters.

A simple synthesis of luminescent π-conjugated materials having fDTBT derivatives

A simple synthesis of luminescent π-conjugated materials having fDTBT derivatives

On-Surface Covalent Synthesis of Carbon Nanomaterials by Harnessing Carbon gem-Polyhalides.

The design of innovative carbon-based nanostructures stands at the forefront of both chemistry and materials science. In this context, π-conjugated compounds are of great interest due to their impact in a variety of fields, including optoelectronics, spintronics, energy storage, sensing and catalysis. Despite extensive research efforts, substantial knowledge gaps persist in the synthesis and characterization of new π-conjugated compounds with potential implications for science and technology. On-surface synthesis has emerged as a powerful discipline to overcome limitations associated with conventional solution chemistry methods, offering advanced tools to characterize the resulting nanomaterials. This review specifically highlights recent achievements in the utilization of molecular precursors incorporating carbon geminal (gem)-polyhalides as functional groups to guide the formation of π-conjugated 0D species, as well as 1D, quasi-1D π-conjugated polymers, and 2D nanoarchitectures. By delving into reaction pathways, novel structural designs, and the electronic, magnetic, and topological features of the resulting products, the review provides fundamental insights for a new generation of π-conjugated materials.

Giant nonlinear optical response of fullerene polymer fragments: a DFT perspective

Organic π-conjugated materials exhibit exceptional nonlinear optical (NLO) properties due to their unique electronic structures, characterized by short response times and large NLO responses. Fullerene (C60) is one of the few polymer species that possess a rich π-conjugated system, making it a promising material with significant NLO responses. In the present paper, we designed three C60 polymer fragments and employed density functional theory to estimate their molecular static first and second hyperpolarizabilities. Compared to previously reported fullerene derivatives, the designed C60 polymer fragments can exhibit notable second-order and third-order molecular NLO responses. The study shows that the hyperpolarizabilities and energy gaps of the investigated C60 polymer fragments are greatly influenced by their topological structures and bonding modes. These findings provide new insights for the design of novel NLO materials based on C60 polymers, and the realization of tunable NLO responses in C60 cluster-based molecular systems, which may have significant applications in nanophotonic devices.

Molecular Packing Topology and Interactions to Decipher Mechanical Compliances in Dicyano-Distyrylbenzene Derivatives.

Flexible optoelectronics is the need of the hour as the market moves toward wearable and conformable devices. Crystalline π-conjugated materials offer high performance as active materials compared to their amorphous counterpart, but they are typically brittle. This poses a significant challenge that needs to be overcome to unfold their potential in optoelectronic devices. Unveiling the molecular packing topology and identifying interaction descriptors that can accommodate strain offers essential guiding principles for developing conjugated materials as active components in flexible optoelectronics. The molecular packing and interaction topology of eight crystal systems of dicyano-distyrylbenzene derivatives are investigated. Face-to-face π-stacks in an inclined orientation relative to the bending surface can accommodate expansion and compression with minimal molecular motion from their equilibrium positions. This configuration exhibits good compliance towards mechanical strain, while a similar structure with a criss-cross arrangement capable of distributing applied strain equally in opposite directions enhances the flexibility. Molecular arrangements that cannot reversibly undergo expansion and compression exhibit brittleness. In the isometric CT crystals, the disproportionate strength of the interactions along the bending plane and orthogonal directions makes these materials sustain a moderate bending strain. These results provide an updated explanation for the elastic bending in semiconducting π-conjugated crystals.

Degradable π-Conjugated Polymers.

The integration of next-generation electronics into society is rapidly reshaping our daily interactions and lifestyles, revolutionizing communication and engagement with the world. Future electronics promise stimuli-responsive features and enhanced biocompatibility, such as skin-like health monitors and sensors embedded in food packaging, transforming healthcare and reducing food waste. Imparting degradability may reduce the adverse environmental impact of next-generation electronics and lead to opportunities for environmental and health monitoring. While advancements have been made in producing degradable materials for encapsulants, substrates, and dielectrics, the availability of degradable conducting and semiconducting materials remains restricted. π-Conjugated polymers are promising candidates for the development of degradable conductors or semiconductors due to the ability to tune their stimuli-responsiveness, biocompatibility, and mechanical durability. This perspective highlights three design considerations: the selection of π-conjugated monomers, synthetic coupling strategies, and degradation of π-conjugated polymers, for generating π-conjugated materials for degradable electronics. We describe the current challenges with monomeric design and present options to circumvent these issues by highlighting biobased π-conjugated compounds with known degradation pathways and stable monomers that allow for chemically recyclable polymers. Next, we present coupling strategies that are compatible for the synthesis of degradable π-conjugated polymers, including direct arylation polymerization and enzymatic polymerization. Lastly, we discuss various modes of depolymerization and characterization techniques to enhance our comprehension of potential degradation byproducts formed during polymer cleavage. Our perspective considers these three design parameters in parallel rather than independently while having a targeted application in mind to accelerate the discovery of next-generation high-performance π-conjugated polymers for degradable organic electronics.

Phosphorescence Properties of Boron/Bismuth Hybrid Conjugated Materials.

By introducing main-group elements such as boron and bismuth to π-conjugated systems, it is possible to modify the optical properties of π-conjugated materials through orbital interactions between the orbital on the elements and π/π*-orbitals, and the heavy atom effect. Moreover, bismuth, which is the heaviest stable element, induces a significant heavy atom effect, making organobismuth compounds promising for applications as phosphorescent materials. In this study, we synthesized new room-temperature phosphorescent materials by incorporating bismuth into thiophene units. The phosphorescence properties of these materials, such as emission lifetime and wavelength, could be further controlled by combining tricoordinate boron with the thienylbismuth structures. The synthesized bismuth- and boron-containing thiophene compounds exhibited phosphorescence at room temperature in both solution and solid states. Furthermore, the introduction of boron raised the energy of the triplet state in the π-conjugated system, resulting in a blue shift of the phosphorescence wavelength. The analysis of photoluminescence properties and TD-DFT calculations revealed that the introduction of bismuth enhances phosphorescence properties, whereas the introduction of boron further promotes intersystem crossing.

Pnictogen-Rich Heterocycles Derived from a Phosphadiazonium Cation.

Heterocycles that pair main group elements and nitrogen are extremely important within the π-conjugated heterocycles research community. Compared to the vast number of boron-nitrogen heterocycles, those that include phosphorus are less common. Furthermore, the use of phosphorus-nitrogen triple bonds of any type to prepare such compounds is unprecedented. Here, we pair pyridyl hydrazonide ligands with phosphadiazonium cations and demonstrate that the chelated Mes*NP group is directly implicated in the photophysical and redox properties observed for the resulting heterocycles. In doing so, we introduce a novel building block for the production of phosphorus-containing heterocycles that could find use in small molecule activation and catalysis or as the functional component of emerging organic electronics.

Mechanistic study of double boron-silicon exchange reactions between dibenzosiloles and boron tribromide.

This paper describes a mechanistic study on double boron-silicon exchange reactions between dibenzosiloles and boron tribromide. This type of reaction presents a safe and environmentally benign approach to convert electron-rich siloles into corresponding electron-deficient boroles and hence shows intriguing potential for the synthesis of boron-doped π-conjugated molecular materials. However, the detailed mechanisms for such reactions have not yet been established in the current literature. In this work, we performed density functional theory (DFT) calculations in conjunction with NMR analysis to unravel the reaction pathways and energy profiles for relevant boron-silicon exchange reactions where two dibenzolesiloles and a phenanthrosilole were employed as reactants, respectively. Our results have shown that excess boron tribromide provides beneficial microsolvation effects on key transition states and reactive intermediates to lower the activation energy barrier for the overall reaction. In the meantime, the substitution pattern at the bay region of the dibenzosilole framework exerts significant impacts on the potential energy surface of the reaction; increased steric hindrance at the bay region decelerates the second boron-silicon exchange step, while extended π-conjugation at the bay region makes the first boron-silicon exchange more challenging. Overall, our computational and experimental results provide an in-depth understanding of the reactivity and scope of this type of reaction, which in turn serves as useful guidance for ongoing research in the field of borole-based organic optoelectronic materials.

Rh(iii)-catalyzed building up of used heterocyclic cations: facile access to white-light-emitting materials.

The first example of rhodium-catalyzed nondirected C-H activation/annulation reactions for the construction of fused heterocyclic cations is reported herein with excellent regioselectivity. Deuterium-labeling experiments indicated that the C(sp3)-H bond cleavage of the N-methyl group might be the rate-limiting step during the reaction process. This protocol provides an opportunity to rapidly access highly π-conjugated fused heterocyclic cations, which opens up a new avenue for efficient screening of single-molecular white-light-emitting materials, pure red-light-emitting materials, and π-conjugated radical materials. Importantly, novel white-light-emitting materials exhibited distinct anti-Kasha dual-emission and could rapidly be fabricated into robust organic and low-cost white light-emitting diodes.

Investigating the diastereoselective synthesis of a macrocycle under Curtin-Hammett control.

This work sheds new light on the stereoselective synthesis of chiral macrocycles containing twisted aromatic units, valuable π-conjugated materials for recognition, sensing, and optoelectronics. For the first time, we use the Curtin-Hammett principle to investigate a chiral macrocyclisation reaction, revealing the potential for supramolecular π-π interactions to direct the outcome of a dynamic kinetic resolution, favouring the opposite macrocyclic product to that expected under reversible, thermodynamically controlled conditions. Specifically, a dynamic, racemic perylene diimide dye (1 : 1 P : M) is strapped with an enantiopure (S)-1,1'-bi-2-naphthol group (P-BINOL) to form two diastereomeric macrocyclic products, the homochiral macrocycle (PP) and the heterochiral species (PM). We find there is notable selectivity for the PM macrocycle (dr = 4 : 1), which is rationalised by kinetic templation from intramolecular aromatic non-covalent interactions between the P-BINOL π-donor and the M-PDI π-acceptor during the macrocyclisation reaction.

π-Conjugated oligofuran macrocycles.

This Feature Article overviews a new class of π-conjugated materials - macrocyclic furans. Starting from their synthesis, we review their unique structural, optical and electronic properties, chemical reactivity, and potential application as synthons. Finally, we discuss the study of oligofuran macrocycles as a model system for exploring the concept of global aromaticity and the size limitation of Hückel's rule in neutral macrocycles.

Design of Chlorinated Indaceno[1,2-b:5,6-b']dithiophene Acceptors toward Efficient Organic Photovoltaics.

Chlorinated modifications have been extensively employed to modulate the optoelectronic properties of π-conjugated materials. Herein, the Cl substitution in designing nonfullerene acceptors (NFAs) with various bandgaps is studied. Four narrow-bandgap electron acceptors (GS-40, GS-41, GS-42, and GS-43) were synthesized by tuning the electrostatic potential distributions of the molecular conjugated backbones. The optical absorption onset of these NFAs ranges from 900 to 1030 nm. Compared to the nonchlorinated analogue, the introduction of Cl atoms on the core of indaceno[1,2-b:5,6-b'] dithiophene (IDT) and π spacer results in an upward shift of the lowest unoccupied molecular orbital levels and induces a blue shift in the absorption spectra of the NFAs. This alteration facilitates achieving appropriate energy-level alignment and favorable bulk heterojunction morphology when blended with the widely used donor PBDB-TF. The PBDB-TF:GS-43-based solar cells show an optimal power conversion efficiency of 13.3%. This work suggests the potential of employing chlorine-modified IDT and thiophene units as fundamental building blocks for developing high-performance photoactive materials.

The Synthesis and Properties of Ladder-Type π-Conjugated Compounds with Pyrrole and Phosphole Rings.

The phosphole ring is known as a useful building block for constructing π-conjugated organic materials. Here, we report ladder-type benzophospholo[3,2-b]indole (BPI) derivatives where the phosphole and the pyrrole rings are directly fused. Compounds 8a-8d with different aryl groups on the phosphorous center were successfully synthesized, and the solid-state structure of 8a was confirmed using X-ray crystallographic analysis. The BPIs exhibit relatively high fluorescence quantum yield (Φ 0.50-0.72) and demonstrate a larger Stokes shift compared with a series of benzophospholo[3,2-b]benzoheteroles. The benzophospholo[3,2-b]carbazole derivative 9, which possesses a benzene ring between the phosphole and the pyrrole rings of the BPI, was also synthesized, and its solid-state structure was confirmed using X-ray crystallographic analysis. Compound 9 was found to show a smaller Stokes shift compared with the BPI.

Bromine Substitution Improves the Photothermal Performance of π-Conjugated Phototheranostic Molecules.

NIR-II fluorescence imaging-guided photothermal therapy (PTT) has been widely investigated due to its great application potential in tumor theranostics. PTT is an effective and non-invasive tumor treatment method that can adapt to tumor hypoxia; nevertheless, simple and effective strategies are still desired to develop new materials with excellent PTT properties to meet clinical requirements. In this work, we developed a bromine-substitution strategy to enhance the PTT of A-D-A'-D-A π-conjugated molecules. The experimental results reveal that bromine substitution can notably enhance the absorptivity (ϵ) and photothermal conversion efficiency (PCE) of the π-conjugated molecules, resulting in the brominated molecules generating two times more heat (ϵ808 nm ×PCE) than their unsubstituted counterpart. We disclose that the enhanced photothermal properties of bromine-substituted π-conjugated molecules are a combined outcome of the heavy-atom effect, enhanced ICT effect, and more intense bromine-mediate intermolecular π-π stacking. Finally, the NIR-II tumor imaging capability and efficient PTT tumor ablation of the brominated π-conjugated materials demonstrate that bromine substitution is a promising strategy for developing future high-performance NIR-II imaging-guided PTT agents.

Heterostructured organic/MoS2 nanowall with synergistic SERS enhancement enabling direct and sensitive detection of contaminants

In recent years, the π-conjugated organic molecular system has attracted considerable attention for its surface-enhanced Raman scattering (SERS) properties. However, the practical application of π-conjugated organic materials as SERS substrates is limited due to the inefficient dissociation of excitons, weak enhancement, and poor reproducibility. Herein, we proposed a novel nanowall SERS heterocomposite based on 3D D(C7CO)-BTBT nanowalls and 2D few-layer MoS2 flakes. A significant SERS activity of the D(C7CO)-BTBT/MoS2 nanowall heterocomposite can be achieved by the charge transfer (CT) resonance enabled by the π-conjugated interactions between D(C7CO)-BTBT and MoS2 and the electromagnetic field spatial distribution induced by the D(C7CO)-BTBT nanowalls. The concentration limit of detection (LOD) of the methylene blue (MB) molecules absorbed on the heterostructured D(C7CO)-BTBT/MoS2 nanowall substrate is as low as 8.2 × 10−11 M, which is excellent among the reported organic-based substrates. A practical SERS detection for the 100 nm polystyrene (PS) nanoparticles on the D(C7CO)-BTBT/MoS2 substrates can be down to 4.5 × 105 ng/L, which is exceptional for the real-time monitoring of emerging contaminants based on SERS technology. This research not only provides a new SERS enhancement strategy for organic-based materials, but also may be helpful in exploring a potential candidate for SERS detection of emerging contaminants.

Nanotechnology for brain tumor imaging and therapy based on π-conjugated materials: state-of-the-art advances and prospects.

In contemporary biomedical research, the development of nanotechnology has brought forth numerous possibilities for brain tumor imaging and therapy. Among these, π-conjugated materials have garnered significant attention as a special class of nanomaterials in brain tumor-related studies. With their excellent optical and electronic properties, π-conjugated materials can be tailored in structure and nature to facilitate applications in multimodal imaging, nano-drug delivery, photothermal therapy, and other related fields. This review focuses on presenting the cutting-edge advances and application prospects of π-conjugated materials in brain tumor imaging and therapeutic nanotechnology.

Spatially Resolved Chiroptical Spectroscopies Emphasizing Recent Applications to Thin Films of Chiral Organic Dyes.

Instrumental techniques able to identify and structurally characterize the aggregation states in thin films of chiral organic π-conjugated materials, from the first-order supramolecular arrangement up to the microscopic and mesoscopic scale, are very helpful for clarifying structure-property relationships. Chiroptical imaging is currently gaining a central role, for its ability of mapping local supramolecular structures in thin films. The present review gives an overview of electronic circular dichroism imaging (ECDi), circularly polarized luminescence imaging (CPLi), and vibrational circular dichroism imaging (VCDi), with a focus on their applications on thin films of chiral organic dyes as case studies.