Planar Conformation Research Articles

A C 54 B 2 Polycyclic π-System with Bilayer Assembly and Multi-Redox Activity

A C ₅₄ B ₂ Polycyclic π-System with Bilayer Assembly and Multi-Redox Activity

Unfused Acceptors Matching π-Bridge Blocks with Proper Frameworks Enable Over 12% As-Cast Organic Solar Cells.

Emerging unfused-ring acceptors (UFAs) have been explored in pursuit of low-cost high-efficient organic solar cells (OSCs). Assembling unfused building blocks into proper frameworks are challenging for the molecular design of UFAs. The authors report herein four UFAs adopting either dithiophene cyclopentadiene (DTC) or dithieno[3,2-b:2',3'-d]pyrrole (DTP) as π-bridge units with different molecular frameworks for high-efficient as-cast OSCs. All these acceptors exhibit strong near-infrared absorption and narrow optical band gap (Eg opt <1.50eV).DTC-bridged symmetric and DTP-bridged asymmetric UFAs exhibit higher planar conformation as well as suitable miscibility and homogeneous phase separation when blending with polymer donor PBDB-T to promote efficient charge transport in the blends. Their blends with PBDB-T contribute optimal PCE of 12.17% and 11.92% in as-cast OSCs, among the highest values for UFAs based as-cast devices in the literature. Experimental and theoretical simulations systematically reveal the impact of manipulating the molecular framework of UFAs on their conformation, optoelectronic, and photovoltaic performance. The results indicate the matching π-bridge units with molecular frameworks as an attractive approach to design UFAs for high-performance as-cast OSCs.

Unravelling the Role of Electron Acceptors for the Universal Enhancement of Charge Transport in Quinoid‐Donor‐Acceptor Polymers for High‐Performance Transistors

AbstractThe quinoid‐donor‐acceptor (Q‐D‐A) strategy has recently emerged as a promising approach for constructing high mobility semiconducting polymers. In order to fully explore the potential of this strategy in improving the charge transport and elucidating the structure‐property‐performance relationships in Q‐D‐A polymers, a series of new polymers with different electron acceptor units and backbone coplanarity have been synthesized and characterized. All of the resulting Q‐D‐A polymers exhibit much more planar backbone conformations in comparison to their donor‐acceptor (D‐A) counterparts. Moreover, organic field‐effect transistors based on Q‐D‐A polymers exhibit excellent effective hole mobilities in a range of 0.44 to 3.35 cm2 V−1 s−1, most of which are orders of magnitude higher than those of their corresponding D‐A polymers. Notably, the hole mobility of 3.35 cm2 V−1 s−1 is among the highest for the quinoidal‐aromatic polymers characterized by conventional spin‐coating methods. Furthermore, the role of electron acceptors in Q‐D‐A polymers has been comprehensively investigated. Polymers with stronger acceptor units are more inclined to deliver edge‐on lamellas, high film crystallinity, small effective hole masses, and decent operational stability. The detailed structure‐property‐device performance relationship will pave the way toward high performance semiconducting polymers using the potent Q‐D‐A strategy.

Conformation-related excited-state charge transfer/separation of donor-π-acceptor chromophores.

Understanding the excited-state charge transfer/separation (CT/CS) of donor-π-acceptor chromophores can provide guidance for designing and synthesizing advanced dyes to improve the performance of dye-sensitized solar cells (DSSCs) in practical applications. Herein, two newly synthesized electronic push-pull molecules, CS-14 and CS-15, that consist of carbazole donor and benzothiadiazole acceptor segments are chosen to explore the ultrafast dynamics of intramolecular CT/CS processes. The theoretical calculation results depict an excited-state intramolecular CT character for both dyes, while the dihedral angle between donor and acceptor of CS-14 is larger than that of CS-15, suggesting a more significant CT character of CS-14. Furthermore, compared to CS-14, the bond rotation of CS-15 between donor and π-bridge is restricted by employing the hexatomic ring, indicating the stronger molecular planarization of CS-15. Ultrafast spectroscopy clearly shows a solvent polarity-dependent excited-state species evolution from CT to CS-the CT character is observed in low-polar toluene solvent, while the feature of the CS state in polar tetrahydrofuran and acetone solvents is captured, which successfully proved a solvent polarity modulated excited-state CT/CS characters. We also found that though the generation of the CS state within CS-14 is slightly faster than that of CS-15, the charge recombination process of CS-15 with excellent planar conformation is much slower, providing enough time for a higher charge migration efficiency in DSSCs.

Approaches toward Atropisomerically Stable and Conformationally Pure Diarylamines.

Diarylamines possess two potentially atropisomeric C-N axes; however, there are few examples of atropisomerically stable diarylamines in the literature, as the contiguous axes can allow for low energy racemization pathways via concerted bond rotations. Herein, we describe highly atropisomerically stable diarylamines that possess barriers to racemization of 30-36 kcal/mol, corresponding to half-lives to racemization on the decade to century time scale at room temperature. Investigation of the factors that led to the high stereochemical stability suggests that increased conjugation of the aniline lone pair of electrons into a more electron-deficient aryl ring, coupled with intramolecular hydrogen-bonding, locked the corresponding axis into a defined planar conformation, disfavoring the lower energy racemization pathways.

Coverage-dependent study of nickel tetraphenyl-porphyrin on Au(332) and Au(788)

The coverage-dependent self-assembly of Nickel-tetraphenyl porphyins on Gold vicinal surfaces was studied by scanning tunneling microscopy. On Au(788) the molecular self-assembly is square-shaped, following the molecular symmetry. On Au(332) the molecules nucleate in a parallelogram lattice for monolayer coverage and in a squared lattice for multilayer coverage. Depending on the vicinal surface the molecules adopt either a saddle shaped or a more planar conformation. The experiments demonstrate that crystallographic direction, terrace sizes and coverage are important in establishing different assembly geometries.

Synthesis, characterizations and photovoltaic applications of a thickness-insensitive benzodifuran based copolymer

Low toleration of thickness variations in the organic solar cells (OSCs), is currently becoming bottleneck challenges to achieve power conversion efficiencies (PCE) and large-scaled roll-to-roll device fabrication. In this work, a new thienyl-free furan-based copolymer of PBDFDFBO was synthesized via Stille copolymerization of benzodifuran (BDF) and 4,7-di(furan-2-yl)benzo[c][1,2,5]oxadiazole monomers. It exhibited a high hole mobility of 2.46 × 10−3 cm2 V−1 S−1, which could be attributed to a planar molecular conformation of the polymer. When the polymer was selected as donor and small molecular ITIC-F as acceptor, the photovoltaic device results showed a champion PCE of 11.53% with a high Voc and FF. Impressively, device efficiency is insensitive to the variation of photoactive layer thickness and can maintain over 10.98% efficiency as film thickness increases to 600 nm, which is the best result for furan-based OSCs. The features of all furan-based polymer of PBDFDFBO provide great potential in developing thick film photovoltaic device and the efficient molecular design strategy also could be referenced to other photovoltaic materials.

A C 54 B 2 Polycyclic π-System with Bilayer Assembly and Multi-Redox Activity

Open AccessCCS ChemistryRESEARCH ARTICLE21 Apr 2022A C54B2 Polycyclic π-System with Bilayer Assembly and Multi-Redox Activity Liuzhong Yuan, Jiaxiang Guo, Yue Yang, Kaiqi Ye, Chuandong Dou and Yue Wang Liuzhong Yuan Google Scholar More articles by this author , Jiaxiang Guo Google Scholar More articles by this author , Yue Yang Google Scholar More articles by this author , Kaiqi Ye Google Scholar More articles by this author , Chuandong Dou Google Scholar More articles by this author and Yue Wang Google Scholar More articles by this author https://doi.org/10.31635/ccschem.022.202201738 SectionsSupplemental MaterialAboutPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Doping heteroatoms into polycyclic aromatic hydrocarbons (PAHs) is an efficient strategy to achieve fascinating electronic structures and materials. However, nanoscale B-doped PAHs remain very challenging, because of the intrinsic instability of the boron atom and the lack of suitable precursors. In this study, we reported a C54B2 polycyclic π-system where one 1,4-diboron-substituted benzene subunit is embedded, which was successfully synthesized from doubly B-doped heptazethrene. This molecule represents not only the largest B-doped PAH by far but also an unprecedented B-doped nanographene. The fully zigzag-armchair edged structure creates its planar conformation, thus leading to the unique bilayer assembly behavior. More importantly, it possesses intriguing electronic structure and optoelectronic properties, such as very broad light absorption that covers 350–750 nm but sharp near-infrared fluorescence with a band width of only 26 nm, as well as reversible five-step redox capability, all of which are rarely observed for other B-doped PAHs. In addition, this molecule displays distinctive local aromaticity that cannot be reproduced via the reduction manipulation of all-carbon congener. Download figure Download PowerPoint Previous articleNext article FiguresReferencesRelatedDetails Issue AssignmentNot Yet AssignedSupporting Information Copyright & Permissions© 2022 Chinese Chemical Society Downloaded 184 times PDF DownloadLoading ...

Layer-by-layer and non-halogenated solvent processing of benzodithiophene-free simple polymer donors for organic solar cells

High performance and easy-synthesis benzodithiophene (BDT)-free simple active layer materials, green non-halogen solvent processing and convenient device fabrication with batch-to-bath stability are all crucial to realize the industrial production of organic solar cells (OSCs) in the future. In this work, we develop two BDT-free polymer donors, PBTz-TC and PBTz-TTC, for green halogen-free solvent and layer-by-layer (LBL) processed high performance OSCs. The strong molecular aggregation of BTz units helps to improve the crystallinity and film-forming properties of the polymers, while the introduction of ester groups assists in enhancing the solubility of conjugated polymers in both halogen and non-halogen solvents and down-shifting the energy levels. The synergistic implementation of LBL method and orthogonal solvents can significantly reduce the scouring effect during the sequential deposition process, which is conducive to construct planar heterojunction. Due to the more planar conformation, PBTz-TTC possesses more robust film-forming property with superior corrosion resistance to the upper-layer than PBTz-TC. While, PBTz-TC better balances the independent film formation and moderate miscibility with IT-4F acceptor to favor stronger interaction at the donor/acceptor interfaces. Consequently, PBTz-TC shows much better performance than PBTz-TTC in both bulk heterojunction and LBL devices, ascribed to the better energy alignment, more favorable morphology and more efficient charge dynamic process. Notably, when treated with halogen-free solvent, an outstanding power conversion efficiency (PCE) of 12.81% with improved stability is achieved for PBTz-TC/IT-4F-based LBL device, which is the highest value of non-halogenated solvent processed devices based on benzodithiophene-free simple polymer donors. These findings provide a guideline for rational design of the environmental friendly simple polymer donor materials for further acceleration of the industrial production of OSCs.

Crystal Structures of Lignocellulosic Furfuryl Biobased Polydiacetylenes with Hydrogen-Bond Networks: Influencing the Direction of Solid-State Polymerization through Modification of the Spacer Length.

We present the topochemical polymerization of two lignocellulosic biobased diacetylenes (DAs) that only differ by an alkyl spacer length of 1 methylene (n = 1) or 3 methylene units (n = 3) between the diyne and carbamate functionalities. Their crystalline molecular organizations have the distinctive feature of being suitable for polymerization in two potential directions, either parallel or skewed to the hydrogen-bonded (HB) network. However, single-crystal structures of the final polydiacetylenes (PDAs) demonstrate that the resulting orientation of the conjugated backbones is different for these two derivatives, which lead to HB supramolecular polymer networks (2D nanosheets) for n = 1 and to independent linear PDA chains with intramolecular HBs for n = 3. Thus, spacer length modification can be considered a new strategy to influence the molecular orientation of conjugated polymer chains, which is crucial for developing the next generation of materials with optimal mechanical and optoelectronic properties. Calculations were performed on model oligodiacetylenes to evaluate the cooperativity effect of HBs in the different crystalline supramolecular packing motifs and the energy profile related to the torsion of the conjugated backbone of a PDA chain (i.e., its ability to adopt planar or helical conformations).

Supramolecular Polymerization of a Photo-Fluttering Chiral Monomer: A Temporarily Suspendable Chain Growth by Light.

Using a photochemically fluttering thiophene-fused cyclooctatetraene derivative (COT) as a nonplanar chiral monomer, we have succeeded in remotely suspending the supramolecular polymerization in a temporal manner by a completely new strategy. The COT monomer with an 8π electron core adopts a saddle shape in the ground state and flutters 5.8 × 103 times faster upon photoirradiation than in the dark as a result of the stabilized planar conformation by the excited-state aromaticity (Baird aromaticity). Detailed investigation revealed that without photoirradiation the rate constant of the fluttering motion is 1/560 times smaller than that of the chain elongation, indicating that the fluttering of COT does not affect the chain elongation in the dark. In contrast, under photoirradiation (365 nm), the fluttering of COT is at least 11 times more rapid than the chain elongation, thereby suppressing the elongation event. The rapid fluttering of COT to suspend the chain elongation is not accompanied by a decrease in active monomer concentration, leading to depolymerization.

Mechanical properties and highly-ordered structural analysis of elastic poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] fibers fabricated by partially melting crystals

Poly[( R )-3-hydroxybutyrate- co -( R )-3-hydroxyvalerate] (P(3HB- co -3HV)) elastic fibers were prepared at temperatures close to or below the melting temperature by partially melting thin crystals with no associated reduction in molecular weight. The obtained fibers exhibited elastic properties and good long-term stability of their mechanical properties, even after aging for 330 days. Cycle tests were conducted with simultaneous in-situ wide-angle X-ray diffraction and small-angle X-ray scattering using synchrotron radiation to investigate the mechanisms governing these fibers’ elasticity. It was determined that the main factor contributing to the elasticity is the reversibility between the random coil structure of tie molecules and the planar zigzag conformation of molecular chains in response to loading and unloading. • P(3HB- co -3HV) elastic fibers were prepared at temperatures below T m . • Elastic fibers exhibited good long-term stability of their mechanical properties. • Cycle tests were conducted with simultaneous in situ WAXD/SAXS measurements. • The generation mechanism of elasticity is proposed.

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Non-fused medium bandgap electron acceptors for efficient organic photovoltaics

The cost-effective organic semiconductors are strongly needed in organic photovoltaics (OPVs). Herein, two medium bandgap (MBG) electron acceptors, TPT4F and TPT4Cl are developed via the new design of multi-noncovalent interaction assisted unfused core, flanked with two electron withdrawing end groups. These fullly non-fused MBG acceptors adapt the planar and rigid conformation in solid, therefore exhibiting the ordered face-on stacking and strong photoluminescence in films. As results, TPT4Cl-based OPVs, upon blending with the PBDB-TF polymer donor, have achieved a power conversion efficiency of 10.16% with a low non-radiative loss of 0.27 eV, representing one of the best fullly non-fused medium bandgap acceptors with desirable cost-efficiency balance.

Isomeric Nonfullerene Acceptors: Planar Conformation Leading to a Higher Efficiency

Isomeric Nonfullerene Acceptors: Planar Conformation Leading to a Higher Efficiency

Covalent Organic Frameworks with Record Pore Apertures.

The pore apertures dictate the guest accessibilities of the pores, imparting diverse functions to porous materials. It is highly desired to construct crystalline porous polymers with predesignable and uniform mesopores that can allow large organic, inorganic, and biological molecules to enter. However, due to the ease of the formation of interpenetrated and/or fragile structures, the largest pore aperture reported in the metal-organic frameworks is 8.5 nm, and the value for covalent organic frameworks (COFs) is only 5.8 nm. Herein, we construct a series of COFs with record pore aperture values from 7.7 to 10.0 nm by designing building blocks with large conformational rigidness, planarity, and suitable local polarity. All of the obtained COFs possess eclipsed stacking structures, high crystallinity, permanent porosity, and high stability. As a proof of concept, we successfully employed these COFs to separate pepsin that is ∼7 nm in size from its crudes and to protect tyrosinase from heat-induced deactivation.

Organosulfur/Selenium-Based Highly Fluorogenic Molecular Probes for Live-Cell Nucleolus Imaging.

We present fluorogenic cationic organo chalcogens that are highly selective to RNA. We have demonstrated that the conformational dynamics and subsequently the optical properties of these dyes can be controlled to facilitate efficient bioimaging. We report the application of organoselenium and organosulfur-based cell-permeable red-emissive probes bearing a favorable cyclic sidearm for selective and high contrast imaging of cell nucleoli. The probes exhibit high quantum yield upon interacting with RNA in an aqueous solution. An in-depth multiscale simulation study reveals that the prominent rotational freezing of the electron-donating sidearm of the probes in the microenvironment of RNA helps in attaining more planar conformation when compared to DNA. It exerts a greater extent of intramolecular charge transfer and hence leads to enhanced fluorescence emission. A systematic structure-interaction relationship study highlighted the impact of heavy-chalcogens toward the improved emissive properties of the probes.

A novel colorimetric and ratiometric fluorescent probe for fluoride anions based on perylene tetra-(alkoxycarbonyl) derivatives

A novel fluoride anion (F−) colorimetric and ratiometric fluorescent probe (AOP) based on perylene tetra-(alkoxycarbonyl) derivative was designed, synthesized and characterized. Probe AOP selectively detected F− with unique absorption and fluorescence changes, which were not observable for other halides and anions (Cl−, Br−, I−, AcO−, SO42−, and ClO4−). The system was studied by 1H NMR, electrochemical, and density functional to determine the properties of the interaction between AOP and F−. Planar conformation and D-A type of AOP facilitated efficient intramolecular charge transfer, resulting in red shifts of absorption/emission spectrum and ratio fluorescent response. Finally, the use of silica coated slides of the AOP to detect F− was also reported.

The Renaissance of Oligothiophene‐Based Donor–Acceptor Polymers in Organic Solar Cells

AbstractThe power conversion efficiencies (PCEs) of organic solar cells (OSCs) have increased rapidly owing to the development of non‐fullerene acceptors (NFAs). However, the development of polymer donors lags behind significantly. Currently, the polymer donors are dominated by a handful of thiophene‐substituted benzo[1,2‐b:4,5‐b']dithiophene (BDTT) polymers, which suffer from lengthy synthesis and high production cost. Compared with BDTT‐based polymers, oligothiophene‐based donor‐acceptor polymers feature much easier synthesis, which were the prevailing polymer donors in fullerene‐based OSCs, but almost disappeared in non‐fullerene OSCs. Herein, two oligothiophene‐based donor‐acceptor polymers (PTTz‐3HD and PTTz‐4HD) are reported to re‐evaluate this kind of polymer in non‐fullerene OSCs. Benefiting from the exquisite alkyl chain design, the polymer PTTz‐3HD exhibits more planar conformation, stronger aggregation, and higher crystallinity, which in turn contributes to the formation of an optimal active layer morphology when blended with NFA. As a result, a PCE of 16.1% and 16.7% is achieved by PTTz‐3HD in binary and ternary OSCs, respectively. Of particular note, the product of short‐circuit current density and fill factor of PTTz‐3HD is fully comparable to those of BDTT‐based polymers. These results suggest the renaissance of oligothiophene‐based donor‐acceptor polymers in OSCs and demonstrate a promising avenue to access high‐efficiency OSCs from low‐cost materials.

Mechano-responsive D–A luminogen based on bisarylic methanone derivative with brightly tricolored mechanochromic luminescence

A new luminogen PTZ-BZ-DBF bearing an electron donor phenothiazine unit and an electron acceptor carbonyl group is designed and synthesized. This molecule adopts highly twisted molecular conformation and exhibits intramolecular charge transfer (ICT), effective solid-state luminescence, and high contrast mechanofluorochromic (MFC) properties. The as-prepared powders show bright yellow-green fluorescence. Under conditions of external mechanical stimulation, the color changes to bright orange-red, and a red shift of 87 nm is observed in the emission spectral profile. Meanwhile, the solid-state luminescence efficiency increases from 20.5% to 28.5%. It is different from general MFC materials, when fumed using DCM vapor or annealed at 150 °C, the fluorescence peaks blue shift to approximately 560 nm, and the yellowish-emitting Y-powders are obtained. The ground solids and Y-powders can be converted to the as-prepared solid powders following the process of solvent recrystallization. Thus, tricolor switching is realized. The results obtained using the PXRD and DSC techniques indicate that the MFC phenomenon can be attributed to the process of crystalline-to-amorphous transition. The red shift of the PL spectra is attributed to the planar intramolecular charge transfer (PICT) process induced by conformational planarization in response to external forces.