Fully conjugated ladder polymers

Copper-mediated construction of benzothieno[3,2-b]benzofurans by intramolecular dehydrogenative C-O coupling reaction

An efficient method to synthesize benzothieno[3,2-b]benzofurans via intramolecular dehydrogenative C-H/O-H coupling has been developed. Good to excellent yields (64-91%) could be obtained no matter if the substituted group is electron-donating or electron-withdrawing. Notably, three-to-six fused ring thienofuran compounds could be constructed using this method. A reaction mechanism study showed that 1,1-diphenylethylene can completely inhibit the reaction. Therefore, it is a radical pathway initiated by single electron transfer between the hydroxyl of the substrate and the copper catalyst.

Experimental and Computational Studies of Azo Dye-Modified Luminol Oligomers: Potential Application in Lithium Ion Sensing

With a view to design novel conjugated oligomers via a facile technique for its possible application in sensors, the present work reports oligomerization of Bismarck Brown (BB) dye with luminol. The structure was confirmed via IR studies, while the electronic transitions were confirmed by UV-visible studies. Morphological studies were carried out via SEM. Computational studies were carried out using the DFT method with a B3LYP 6-311G(d) basis set to investigate the optimized geometry, band gap, and vibrational and electronic transitions data. The HOMO-LUMO energies showed significant reduction in the band gap upon increasing the content of BB dye. The computational IR and UV spectra were noticed to be in close agreement with the experimental results. Spectrophotometric determination of Li ion was attempted using lithium chloride and a lithium carbonate drug commonly used in the treatment of bipolar disorder. The detection limit was noticed to be as low as 5.1 × 10-6 M, which could be used to design a Li ion sensor.

Synthesis of bent-shaped π-extended thienoacenes from 2,5-distannylated 3,4-dialkynethiophene

Bent-shaped thienoacenes show promise as next-generation organic semiconductors. Here we present the synthesis of an air-stable, pure and easily scalable thiophene precursor, 2,5-distannylated-3,4-dialkyne thiophene, starting from 3,4-dialkyne thiophene in quantitative yields. This precursor has been used for the synthesis of a versatile class of syn-thienoacenes comprising up to 13 fused rings, helical acenes and donor-acceptor acenes.

Pushing the Limits of Flexibility and Stretchability of Solar Cells: A Review

Emerging forms of soft, flexible, and stretchable electronics promise to revolutionize the electronics industries of the future offering radically new products that combine multiple functionalities, including power generation, with arbitrary form factor. For example, skin-like electronics promise to transform the human-machine-interface, but the softness of the skin is incompatible with traditional electronic components. To address this issue, new strategies toward soft and wearable electronic systems are currently being pursued, which also include stretchable photovoltaics as self-powering systems for use in autonomous and stretchable electronics of the future. Here recent developments in the field of stretchable photovoltaics are reviewed and their potential for various emerging applications are examined. Emphasis is placed on the different strategies to induce stretchability including extrinsic and intrinsic approaches. In the former case, engineering and patterning of the materials and devices are key elements while intrinsically stretchable systems rely on mechanically compliant materials such as elastomers and organic conjugated polymers. The result is a review article that provides a comprehensive summary of the progress to date in the field of stretchable solar cells from the nanoscale to macroscopic functional devices. The article is concluded by discussing the emerging trends and future developments.

Ladder Phenylenes Synthesized on Au(111) Surface via Selective [2+2] Cycloaddition

Ladder phenylenes (LPs) composed of alternating fused benzene and cyclobutadiene rings have been synthesized in solution with a maximum length no longer than five units. Longer polymeric LPs have not been obtained so far because of their poor stability and insolubility. Here, we report the synthesis of linear LP chains on the Au(111) surface via dehalogenative [2+2] cycloaddition, in which the steric hindrance of the methyl groups in the 1,2,4,5-tetrabromo-3,6-dimethylbenzene precursor improves the chemoselectivity as well as the orientation orderliness. By combining scanning tunneling microscopy and noncontact atomic force microscopy, we determined the atomic structure and the electronic properties of the LP chains on the metallic substrate and NaCl/Au(111). The tunneling spectroscopy measurements revealed the charged state of chains on the NaCl layer, and this finding is supported by density functional theory calculations, which predict an indirect bandgap and antiferromagnetism in the polymeric LP chains.

Evidence of C-F···H-C Attractive Interaction: Enforced Coplanarity of a Tetrafluorophenylene-Ethynylene-Linked Porphyrin Dimer

The formation of C-F···H-C "hydrogen bonds" has been a controversial subject because, in principle, fluorine is hardly an acceptor for less acidic protons contrasting to the C-F···H-O and C-F···H-N hydrogen bonds. Nevertheless, the interaction is emerging as a powerful implement for confining the torsional rotation in the design of fully coplanar π-conjugated polymers. Heretofore, no evidence of the C-F···H-C interaction has been observed in solutions. We herein disclose comprehensive evidence that the C-F···H-C interaction produces an attractive force. A ¹⁹F-¹H heteronuclear Overhauser effect experiment elucidated the close proximity of the F and H atoms in the doubly edge-facing C-F···H-C interactions of a meso-tetrafluorophenylene-ethynylene-conjugated porphyrin dimer (1). Extensive electronic and photophysical property investigations confirmed that all the aromatic units were torsionally restricted by the C-F···H-C interactions. Moreover, the enforced coplanarity invoked a markedly high π-staking propensity. Thus, we have firmly established the formation of a C-F···H-C interaction that produces a hydrogen-bond-like attractive force in solution.

Pyrrole-Embedded Linear and Helical Graphene Nanoribbons

Linear and helical graphene nanoribbons (L-PyGNR and H-PyGNR) bearing electron-rich pyrrole units have been synthesized by using the photochemical cyclodehydrochlorination (CDHC) reaction. The pyrrole units in the polymer backbone make the polymer electron-rich with moderate bandgap values and relatively high HOMO energy levels. The planarization of the pyrrole unit through cyclization yields a bandgap value almost 0.5 eV lower than that measured for polypyrrole. Conductivity values in the thin film up to 0.12 S/cm were measured for the chemically oxidized L-PyGNR (four-point method). Both GNRs showed excellent fluorescence sensing properties for TNT in solution with K_SV values up to 6.4 × 10⁶ M^-1.

On-surface synthesis of π-conjugated ladder-type polymers comprising nonbenzenoid moieties

On-surface synthesis provides a powerful approach toward the atomically precise fabrication of π-conjugated ladder polymers (CLPs). We report herein the surface-assisted synthesis of nonbenzenoid CLPs from cyclopenta-annulated anthracene monomers on Au(111) under ultrahigh vacuum conditions. Successive thermal annealing steps reveal the dehalogenative homocoupling to yield an intermediate 1D polymer and the subsequent cyclodehydrogenation to form the fully conjugated ladder polymer. Notably, neighbouring monomers may fuse in two different ways, resulting in six- and five-membered rings, respectively. The structure and electronic properties of the reaction products have been investigated via low-temperature scanning tunneling microscopy and spectroscopy, complemented by density-functional theory calculations. Our results provide perspectives for the on-surface synthesis of nonbenzenoid CLPs with the potential to be used for organic electronic devices.

Effective Synthesis of Ladder-type Oligo(p-aniline)s and Poly(p-aniline)s via Intramolecular SNAr Reaction

Symmetric ladder-type oligo(p-aniline)s and poly(p-aniline)s were successfully synthesized by an intramolecular ring closure in a highly efficient S_NAr reaction from oligo(p-phenylene)s and poly(p-phenylene)s with fluorine (F) and secondary amine (NH) groups. Unlike Cadogan ring closure, the newly designed cyclization reaction will not produce a mixture of symmetric and nonsymmetric structures. Moreover, the introduction of the F atom does not hinder Suzuki polymerization. The result indicates that preparing regular oligomers and polymers with a nitrogen bridge is possible.

Polymers with advanced structural and supramolecular features synthesized through topochemical polymerization

Polymers are an integral part of our daily life. Hence, there are constant efforts towards synthesizing novel polymers with unique properties. As the composition and packing of polymer chains influence polymer's properties, sophisticated control over the molecular and supramolecular structure of the polymer helps tailor its properties as desired. However, such precise control via conventional solution-state synthesis is challenging. Topochemical polymerization (TP), a solvent- and catalyst-free reaction that occurs under the confinement of a crystal lattice, offers profound control over the molecular structure and supramolecular architecture of a polymer and usually results in ordered polymers. In particular, single-crystal-to-single-crystal (SCSC) TP is advantageous as we can correlate the structure and packing of polymer chains with their properties. By designing molecules appended with suitable reactive moieties and utilizing the principles of supramolecular chemistry to align them in a reactive orientation, the synthesis of higher-dimensional polymers and divergent topologies has been achieved via TP. Though there are a few reviews on TP in the literature, an exclusive review showcasing the topochemical synthesis of polymers with advanced structural features is not available. In this perspective, we present selected examples of the topochemical synthesis of organic polymers with sophisticated structures like ladders, tubular polymers, alternating copolymers, polymer blends, and other interesting topologies. We also detail some strategies adopted for obtaining distinct polymers from the same monomer. Finally, we highlight the main challenges and prospects for developing advanced polymers via TP and inspire future directions in this area.

Acene Ring Size Optimization in Fused Lactam Polymers Enabling High n-Type Organic Thermoelectric Performance

Three n-type fused lactam semiconducting polymers were synthesized for thermoelectric and transistor applications via a cheap, highly atom-efficient, and nontoxic transition-metal free aldol polycondensation. Energy level analysis of the three polymers demonstrated that reducing the central acene core size from two anthracenes (A-A), to mixed naphthalene-anthracene (A-N), and two naphthalene cores (N-N) resulted in progressively larger electron affinities, thereby suggesting an increasingly more favorable and efficient solution doping process when employing 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (N-DMBI) as the dopant. Meanwhile, organic field effect transistor (OFET) mobility data showed the N-N and A-N polymers to feature the highest charge carrier mobilities, further highlighting the benefits of aryl core contraction to the electronic performance of the materials. Ultimately, the combination of these two factors resulted in N-N, A-N, and A-A to display power factors (PFs) of 3.2 μW m^-1 K^-2, 1.6 μW m^-1 K^-2, and 0.3 μW m^-1 K^-2, respectively, when doped with N-DMBI, whereby the PFs recorded for N-N and A-N are among the highest reported in the literature for n-type polymers. Importantly, the results reported in this study highlight that modulating the size of the central acene ring is a highly effective molecular design strategy to optimize the thermoelectric performance of conjugated polymers, thus also providing new insights into the molecular design guidelines for the next generation of high-performance n-type materials for thermoelectric applications.

Silicon and oxygen synergistic effects for the discovery of new high-performance nonfullerene acceptors

In organic electronics, an aromatic fused ring is a basic unit that provides π-electrons to construct semiconductors and governs the device performance. The main challenge in developing new π-skeletons for tuning the material properties is the limitation of the available chemical approach. Herein, we successfully synthesize two pentacyclic siloxy-bridged π-conjugated isomers to investigate the synergistic effects of Si and O atoms on the geometric and electronic influence of π-units in organic electronics. Notably, the synthesis routes for both isomers possess several advantages over the previous approaches for delivering conventional aromatic fused-rings, such as environmentally benign tin-free synthesis and few synthetic steps. To explore their potential application as photovoltaic materials, two isomeric acceptor-donor-acceptor type acceptors based on these two isomers were developed, showing a decent device efficiency of 10%, which indicates the great potential of this SiO-bridged ladder-type unit for the development of new high-performance semiconductor materials.

Tailoring π-conjugation and vibrational modes to steer on-surface synthesis of pentalene-bridged ladder polymers

The development of synthetic strategies to engineer π-conjugated polymers is of paramount importance in modern chemistry and materials science. Here we introduce a synthetic protocol based on the search for specific vibrational modes through an appropriate tailoring of the π-conjugation of the precursors, in order to increase the attempt frequency of a chemical reaction. First, we design a 1D π-conjugated polymer on Au(111), which is based on bisanthene monomers linked by cumulene bridges that tune specific vibrational modes. In a second step, upon further annealing, such vibrational modes steer the twofold cyclization reaction between adjacent bisanthene moieties, which gives rise to a long pentalene-bridged conjugated ladder polymer featuring a low bandgap. In addition, high resolution atomic force microscopy allows us to identify by atomistic insights the resonance form of the polymer, thus confirming the validity of the Glidewell and Lloyd´s rules for aromaticity. This on-surface synthetic strategy may stimulate exploiting previously precluded reactions towards π-conjugated polymers with specific structures and properties.

Extraordinary electrochemical stability and extended polaron delocalization of ladder-type polyaniline-analogous polymers

Electrochemical stability and delocalization of states critically impact the functions and practical applications of electronically active polymers. Incorporation of a ladder-type constitution into these polymers represents a promising strategy to enhance the aforementioned properties from a fundamental structural perspective. A series of ladder-type polyaniline-analogous polymers are designed as models to test this hypothesis and are synthesized through a facile and scalable route. Chemical and electrochemical interconversions between the fully oxidized pernigraniline state and the fully reduced leucoemeraldine state are both achieved in a highly reversible and robust manner. The protonated pernigraniline form of the ladder polymer exhibits unprecedented electrochemical stability under highly acidic and oxidative conditions, enabling the access of a near-infrared light-absorbing material with extended polaron delocalization in the solid-state. An electrochromic device composed of this ladder polymer shows distinct switching between UV- and near-infrared-absorbing states with a remarkable cyclability, meanwhile tolerating a wide operating window of 4 volts. Taken together, these results demonstrate the principle of employing a ladder-type backbone constitution to impart superior electrochemical properties into electronically active polymers.

100th Anniversary of Macromolecular Science Viewpoint: Polymerization of Cumulated Bonds: Isocyanates, Allenes, and Ketenes as Monomers

Polymer chemistry offers exciting opportunities to tailor the properties of soft materials through control of the composition of the polymers and their interaction with each other, additives, and surfaces. Ongoing advances in the synthesis of polymeric materials demonstrate the drive for materials with tailored properties for enhanced performance in the next generation of materials and devices. One class of small molecules that can serve as monomers in chain growth polymerization are cumulated double bonds of the general form X═Y═Z. The three most common classes of these molecules are isocyanates (N═C═O), allenes (C═C═C), and ketenes (C═C═O), each of which has been explored as monomers under a variety of conditions. The orthogonality of the two pi bonds of the cumulated double bonds (i.e., lack of conjugation) enables the formation of different polymer backbones from a single monomer, provided the regioreactivity is controlled. This Viewpoint outlines the use of these three cumulated double bonds as monomers, illustrating success and current limitations to established polymerization methods. We then provide an outlook to the future of cumulated double bonds as monomers for the generation of tailored polymer compositions.

Fluoride-Ion-Catalyzed Synthesis of Ladder-type Conjugated Benzobisbenzofurans via Intramolecular Nucleophilic Aromatic Substitution Reaction under Metal-free and Mild Conditions

The fluoride-ion-catalyzed synthesis of benzobisbenzofuran derivatives is described. Fluorine-containing aryl silyl ethers were reacted with 5 mol % of Bu₄NF to give desired compounds in high yield under mild conditions. Syn-selective cyclization reaction was discovered for a particular compound as a kinetic product. Computational analysis revealed that the fluorine substituents in the anti-type benzobisbenzofurans affect the order of the molecular orbitals.

Molecular Semiconductors for Logic Operations: Dead-End or Bright Future?

The field of organic electronics has been prolific in the last couple of years, leading to the design and synthesis of several molecular semiconductors presenting a mobility in excess of 10 cm² V^-1 s^-1 . However, it is also started to recently falter, as a result of doubtful mobility extractions and reduced industrial interest. This critical review addresses the community of chemists and materials scientists to share with it a critical analysis of the best performing molecular semiconductors and of the inherent charge transport physics that takes place in them. The goal is to inspire chemists and materials scientists and to give them hope that the field of molecular semiconductors for logic operations is not engaged into a dead end. To the contrary, it offers plenty of research opportunities in materials chemistry.

Switching of the conformational flexibility of a diazacyclooctane-containing ladder polymer by coordination and elimination of a Lewis acid

We report the first system of ladder polymers capable of interconversion between rigid and flexible conformations by coordination and elimination of a Lewis acid (BPh₂Cl) on diazacyclooctane units in the main chain.

On-surface synthesis of doubly-linked one-dimensional pentacene ladder polymers

On-surface investigations of pentacene molecules functionalized with four dibromomethylene groups reveal, after an annealing step, the formation of π-conjugated ladder polymers doubly-linked by ethynylene bridges on a Au(111) surface.

Metal-free polymerization: synthesis and properties of fused benzo[1,2-b:4,5-b′]bis[b]benzothiophene (BBBT) polymers

A family of fused semiconducting polymers containing the thienoacenes BBBT has been synthesized efficiently by non-metal and environmentally benign polymerization.

Selective synthesis of diazacyclooctane -containing flexible ladder polymers with symmetrically or unsymmetrically substituted side chains

We report a versatile synthetic method for selectively obtaining symmetrical or unsymmetrical N,N′-dialkylated DACO-containing flexible ladder polymers with various functionalities.

Designing dithienonaphthalene based acceptor materials with promising photovoltaic parameters for organic solar cells

Scientists are focusing on non-fullerene based acceptors due to their efficient photovoltaic properties. Here, we have designed four novel dithienonaphthalene based acceptors with better photovoltaic properties through structural modification of a well-known experimentally synthesized reference compound R. The newly designed molecules have a dithienonaphthalene core attached with different acceptors (end-capped). The acceptor moieties are 2-(5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (H1), 2-(5,6-dicyano-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile (H2), 2-(5-methylene-6-oxo-5,6-dihydrocylopenta[c]thiophe-4-ylidene)-malononitrile (H3) and 2-(3-(dicyanomethylene)-2,3-dihydroinden-1-yliden)malononitrile (H4). The photovoltaic parameters of the designed molecules are discussed in comparison with those of the reference R. All newly designed molecules show a reduced HOMO-LUMO energy gap (2.17 eV to 2.28 eV), compared to the reference R (2.31 eV). Charger transfer from donor to acceptor is confirmed by a frontier molecular orbital (FMO) diagram. All studied molecules show extensive absorption in the visible region and absorption maxima are red-shifted compared to R. All investigated molecules have lower excitation energies which reveal high charge transfer rates, as compared to R. To evaluate the open circuit voltage, the designed acceptor molecules are blended with a well-known donor PBDB-T. The molecule H3 has the highest V oc value (1.88 V). TDM has been performed to show the behaviour of electronic excitation processes and electron hole location between the donor and acceptor unit. The binding energies of all molecules are lower than that of R. The lowest is calculated for H3 (0.24 eV) which reflects the highest charge transfer. The reorganization energy value for both the electrons and holes of H2 is lower than R which is indicative of the highest charge transfer rate.

Synthesis and Properties of Conjugated Polymers Based on a Ladderized Anthanthrene Unit

Polycyclic aromatic hydrocarbons (PAHs) are interesting building blocks for the preparation of conjugated polymers due to their extended π surface and planar conformation. However, their use as comonomer in conjugated polymers often leads to nonplanar main chains as a consequence of high steric hindrance at the linking point. Herein, we report the synthesis of a ladderized anthanthrene unit using an sp3 carbon bridge. Three conjugated copolymers with fluorene, isoindigo, and bithiophene derivatives have been synthesized and characterized to study the effect of such ladderization on the electronic properties. The dihedral angle between the ladderized anthanthrene and adjacent units has been significantly reduced by the formation of the sp3 carbon bridge, thus eliminating the steric hindrance with the proton at the peri position of the anthanthrene unit and red-shifting the absorption spectrum by 25 nm.

Photocatalytically active ladder polymers

Conjugated ladder polymers (cLaPs) are introduced as organic semiconductors for photocatalytic hydrogen evolution from water under sacrificial conditions. Starting from a linear conjugated polymer (cLiP1), two ladder polymers are synthesized via post-polymerization annulation and oxidation techniques to generate rigidified, planarized materials bearing dibenzo[b,d]thiophene (cLaP1) and dibenzo[b,d]thiophene sulfone subunits (cLaP2). The high photocatalytic activity of cLaP1 (1307 μmol h-1 g-1) in comparison to that of cLaP2 (18 μmol h-1 g-1) under broadband illumination (λ > 295 nm) in the presence of a hole-scavenger is attributed to a higher yield of long-lived charges (μs to ms timescale), as evidenced by transient absorption spectroscopy. Additionally, cLaP1 has a larger overpotential for proton reduction and thus an increased driving force for the evolution of hydrogen under sacrificial conditions.

Rigid Coplanar Polymers for Stable n-Type Polymer Thermoelectrics

Low n-doping efficiency and inferior stability restrict the thermoelectric performance of n-type conjugated polymers, making their performance lag far behind of their p-type counterparts. Reported here are two rigid coplanar poly(p-phenylene vinylene) (PPV) derivatives, LPPV-1 and LPPV-2, which show nearly torsion-free backbones. The fused electron-deficient rigid structures endow the derivatives with less conformational disorder and low-lying lowest unoccupied molecular orbital (LUMO) levels, down to -4.49 eV. After doping, two polymers exhibited high n-doping efficiency and significantly improved air stability. LPPV-1 exhibited a high conductivity of up to 1.1 S cm^-1 and a power factor as high as 1.96 μW m^-1  K^-2 . Importantly, the power factor of the doped LPPV-1 thick film degraded only 2 % after 7 day exposure to air. This work demonstrates a new strategy for designing conjugated polymers, with planar backbones and low LUMO levels, towards high-performance and potentially air-stable n-type polymer thermoelectrics.

Beyond 1000 nm Emission Wavelength: Recent Advances in Organic and Inorganic Emitters for Deep-Tissue Molecular Imaging

In vivo second near-infrared (NIR-II, 1.0-1.7 µm) bioimaging , a rapidly expanding imaging tool for preclinical diagnosis and prognosis, is of great importance to afford precise dynamic actions in vivo with high spatiotemporal resolution, deeper penetration, and decreasing light absorption and scattering. In the course of preclinical practices, organic and inorganic emitters with NIR-II signals are indispensable keys to open the invisible biological window. In this review, NIR-II emitters, including but not limited to organic emitters like organic small molecules and copolymers, and inorganic emitters such as lanthanide-based nanocrystals, quantum dots like Ag₂ S dots, and carbon nanotubes, are described, especially regarding their unique optical features and noteworthy functions for animal bioimaging. Along with these existing advances, the challenges and potential spaces for further progress are discussed to offer an approximate direction for future researches.

β-Strand inspired bifacial π-conjugated polymers

Access to diverse, relatively high molecular weight soluble linear polymers without pendant solubilizing chains is the key to solution state synthesis of structurally diverse nanoribbons of conjugated materials. However, realizing soluble 1D-π-conjugated polymers without pendant solubilizing chains is a daunting task. Herein, inspired from the polypeptide β-strand architecture, we have designed and developed novel bifacial π-conjugated polymers (M n: ca. 24 kDa) that are soluble (ca. 70 to >250 mM) despite the absence of pendant solubilizing chains. The impact of varying the bifacial monomer height on polymer solubility, optical properties, and interactions with small molecules is reported.

Covalent and Noncovalent Approaches to Rigid Coplanar π-Conjugated Molecules and Macromolecules

Molecular conformation and rigidity are essential factors in determining the properties of individual molecules, the associated supramolecular assemblies, and bulk materials. This correlation is particularly important for π-conjugated molecular and macromolecular systems. Within such an individual molecule, a coplanar conformation facilitates the delocalization of not only molecular orbitals but also charges, excitons, and spins, leading to synergistically ensembled properties of the entire conjugated system. A rigid backbone, meanwhile, imposes a high energy cost to disrupt such a favorable conformation, ensuring the robustness and persistence of coplanarity. From a supramolecular and material point of view, coplanarity and rigidity often promote strong intermolecular electronic coupling and reduce the energy barrier for the intermolecular transport of charges, excitons, and phonons, affording advanced materials properties in bulk. In this context, pursuing a rigid and coplanar molecular conformation often represents one of the primary objectives when designing and synthesizing conjugated molecules for electronic and optical applications. Two general bottom-up strategies-covalent annulation and noncovalent conformational control-are often employed to construct rigid coplanar π systems. These strategies have afforded various classes of such molecules and macromolecules, including so-called conjugated ladder polymers, graphene nanoribbons, polyacenes, and conformationally locked organic semiconductors. While pursuing these targets, however, one often confronts challenges associated with precise synthesis and limited solubility of the rigid coplanar systems, which could further impede their large-scale preparation, characterization, processing, and application. To address these issues, we developed and utilized a number of synthetic methods and molecular engineering approaches to construct and to process rigid coplanar conjugated molecules and macromolecules. Structure-property correlations of this unique class of organic materials were established, providing important chemical principles for molecular design and materials applications. In this Account, we first describe our efforts to synthesize rigid coplanar π systems fused by various types of bonds, including kinetically formed covalent bonds, thermodynamically formed covalent bonds, N→B coordinate bonds, and hydrogen bonds, in order of increasing dynamic character. The subsequent section discusses the characteristic properties of selected examples of these rigid coplanar π systems in comparison with control compounds that are not rigid and coplanar, particularly focusing on the optical, electronic, and electrochemical properties. For systems bridged with noncovalent interactions, active manipulation of the dynamic bonds can tune variable properties at the molecular or collective level. Intermolecular interactions, solid-state packing, and processing of several cases are then discussed to lay the foundation for future materials applications of rigid coplanar π conjugated compounds.