Design and Synthesis of Acceptor-Donor-Acceptor Type Non-Fullerene Acceptors Using Oxindole-Based Bridge for Polymer Solar Cells Applications

Two acceptor-donor-acceptor(A-D-A)type non-fullerene acceptors(namely WH1 and WH7)containing the oxindole-based bridge are designed and synthesized for polymer solar cells(PSCs)applications.The bridge unit is introduced through a precursor(6-bromo-1-octylindoline-2,3-dione)that contains both bromine and carbonyl and provides the feasibility of the Pd-catalyzed cross-coupling reaction and the Knoevenagel condensation,respectively.This facile synthetic approach exhibits the potential to gain high performance non-fullerene acceptors through extendingπ-conjugated backbone with strong light-absorbing building blocks.The synthesis and properties of WH1 and WH7 are demonstrated with different endcap units,then PSCs are fabricated using PBDB-T:WH1 and PBDB-T:WH7 as the active layers,and attain an average power conversion efficiency(PCE)of 2.58%and 6.24%,respectively.Further device physics studies afford the deep insight of structure variation influence on the device performance.This work provides a facile non-fullerene acceptor design strategy and shows how structure variations impact the PSC performance.

Electropolymerizable Conjugated Polymers with High Contrast in Infrared Region

Two conjugated molecules have been designed and synthesized for preparing electrochromic thin film devices on the surface of electrodes through electropolymerization. These devices exhibit good contrast at around 80% in mid-infrared region and rapid response time, especially EP02 which could be switched between on and off state in around 1 s. The interesting electrochromic properties and easy processable properties open the door to electrochromic applications using large or flexible surfaces such as IR shutters and apertures.

Open-Shell Oligomers and Polymers: Theory, Characterization Methods, Molecular Design, and Applications

Open-shell oligomers and polymers have exhibited intriguing electronic and magnetic properties, making them highly desirable for a wide range of applications, including ambipolar organic field-effect transistors (OFETs), photodetectors, organic thermoelectrics, and spintronics. Although open-shell ground states have been observed in certain small molecules and doped organic semiconductors, the exploration of open-shell ground-state conjugated polymers is still limited, and the strategies for designing these polymers remain obscure. This review aims to briefly introduce the theory and characterization methods of open-shell conjugated polymers, along with an overview of recent progress and applications. The objective is to stimulate further advancements and investigations in this promising area by shedding light on the potential of open-shell conjugated polymers and the challenges that lie ahead.

Structural disruption of melanin-like polymers with boosted UV protection

Manipulating the energy structure of materials represents an efficient way to regulate their light absorption behaviors. For example, constructing donor-acceptor(D-A) structures to increase the polarizability and reduce the energy bandgap of local molecules has been widely used in the field of organic photovoltaics with ordered structures. Remarkably, even in disordered and chaotic systems such as melanin-like polydopamine(PDA), visible and near-infrared light absorption can be significantly improved using this strategy. However, there has been a noticeable dearth of research on the ultraviolet(UV) light absorption regulation of bioinspired polymers with disordered and chaotic architectures by tailoring the D-A microstructures. In this study, a series of benzoheterocyclic molecules with strong electron-donating features screened by molecular simulation calculations were involved in disrupting the D-A structures within PDA. The destruction of D-A structures promoted the increase of the energy band gap and finally boosted the UV absorption of PDA. The resulting PDA nanoparticles with enhanced UV absorption were further employed to fabricate UV shielding composite films to protect the growth of plants from harmful UV radiation. This research may open up new avenues for structural disruption of bioinspired polymers for enhanced photoprotection applications.

Carbazole-Based Donor-Acceptor Conjugated Microporous Polymers for Efficient Visible-Light-Driven Photocatalytic H_(2) Evolution

Conjugated microporous polymers (CMPs) featuring extended π-structures, large specific surface area and tailor-made functionalities are a class of promising organic photocatalysts for hydrogen evolution reaction (HER) from water. However, the photocatalytic activities of most CMPs are severely hindered by slow charge transfer rate and fast charge recombination process. Herein, we develop a strategy for the synthesis of donor-acceptor CMPs through nickel(0)-catalyzed Yamamoto cross-coupling of 3,6-dibromo-9-(4-bromophenyl)carbazole (CZ) with 5,5'-dibromo-2,2'-bipyridine (DBPy) for efficient HER from water. The PCZN-4 prepared with a 2 : 3 stoichiometric ratio of CZ to DBPy exhibited the highest photocatalytic hydrogen evolution rate of 7160 μmol·g^(–1)·h^(–1), which was nearly equal to 179 times and 143 times that of PCZN-1 (40 μmol·g^(–1)·h^(–1)) and PCZN-6 (50 μmol·g^(–1)·h^(–1)) obtained by Yamamoto homocoupling of CZ and DBPy, respectively. Compared to the homocoupling counterparts, the enhanced photocatalytic activity of PCZN-4 results from improved separation efficiency of charge carriers. Interestingly, the photocatalytic H2 evolution performance of PCZN-4 could be further improved up to 17080 μmol·g^(–1)·h^(–1) by adjusting pH of the aqueous solution. This work offers a novel approach for improving photocatalytic efficiency by tuning the chemical structures and surrounding microenvironment of the polymer backbone.

Electron donor–acceptor (D-A) tuning to achieve soluble covalent organic polymers for optoelectronic devices

Covalent organic polymers(COPs)have emerged as a unique class of luminescent polymers with pre-designed quasi-ordered architectures.However,their layered stacks and limited solubility preclude further processing for large-scale applications in devices,especially optoelectronic equipment.Herein,a universal strategy to adjust the electron donor–acceptor(D-A)moieties of the building blocks in COPs is proposed,achieved by in situ charge exfoliation of COP blocks into few-layer true solutions in(Lewis)acid and base media.The electron D-A moieties of the building blocks endow the COPs with the ability to accept or donate electrons,by altering the electron cloud distribution as well as the relative energy levels of the frontier molecular orbitals.The resultant soluble COPs can easily be processed into a uniform film by solution processing via the spin-coat method.The obtained COP-N achieves efficient and stable perovskite electroluminescence as a novel hole injection material on indium tin oxide,and the operating lifetime for a perovskite quantum dot light-emitting diodes device exceeds that of a poly(ethylene dioxythiophene):polystyrene sulphonate counterpart.This straightforward electronic regulation strategy provides a new avenue for the rational synthesis of processable reticular molecular polymers for practical electronic devices.

Recent Progress in Donor-Acceptor Type Conjugated Polymers for Organic Field-effect Transistors

The recent progress in the design and synthesis of high-performance donor-acceptor conjugated polymeric semiconducting materials is reviewed from the perspective of multiscale structures.The multiscale of conjugated polymers is from the primary one-dimensional polymer molecular scale to the secondary polymer-chains interaction scale,and then to the tertiary polymer aggregate scale.This review focuses on the design and synthesis of polymer molecules,proposes new classification rules,and rationally summarizes the design strategies and modulation methods of polymers.We describe the recent progress from these three aspects:(1)the modification ofπ-conjugated backbone,(2)the evolution of the polymerization methods,and(3)the regulation of aggregate-state structure.

A Cyano-Substituted Organoboron Electron-deficient Building Block for D-A Type Conjugated Polymers

The development of donor-acceptor(D-A)type conjugated polymers depends largely on the design of novel A building blocks.Herein,we report a novel A building block based on the cyano-substituted organoboron unit(SBN-3).Compared with the most common fluorine-substituted B←N unit,SBN-3 displays a significantly downshifted LUMO energy level because of the strong electron-withdrawing ability of cyano groups.In addition,due to the greater impact of cyano substitution on LUMO than on HOMO,SBN-3 exhibits a reduced band gap,nearinfrared absorption and fluorescence properties.The D-A type conjugated polymers based on the cyano-substituted B←N unit with thiophene-based units show narrow optical band gaps of ca.1.3 e V as well as distinctive electronic structures,i.e.,delocalized LUMOs and localized HOMOs.This work thus provides not only an effective approach to design strong A units but also a new electron-deficient building block for D-A type conjugated polymers.

A"donor–acceptor"structured semiconductor polymer for near infrared fluorescence imaging guided photodynamic therapy

Near infrared(NIR)fluorescence imaging guided photodynamic therapy(PDT)is a technique which has been developed in many clinical trials due to its advantage of real-time optical monitoring,specific spatiotemporal selectivity,and minimal invasiveness.For this,photosensitizers with NIR fluorescence emission and high^(1)O_(2)generation quantum yield are highly desirable.Herein,we designed and synthesized a"donor-acceptor"(D-A)structured semiconductor polymer(SP),which was then wrapped with an amphiphilic compound(Pluronic■F127)to prepare water-soluble nanoparticles(F-SP NPs).The obtained F-SP NPs exhibit good water solubility,excellent particle size stability,strong absorbance at deep red region,and strong NIR fluorescent emission characteristics.The maximal mass extinction coe±cient and fluorescence quantum yield of these F-SPs were calculated to be 21.7 L/(g·cm)and 6.5%,respectively.Moreover,the^(1)O_(2)quantum yield of 89%for F-SP NPs has been achieved under 635 nm laser irradiation,which is higher than Methylene Blue,Ce6,and PpIX.The outstanding properties of these F-SP NPs originate from their unique D-A molecular characteristic.This work should help guide the design of novel semiconductor polymer for NIR fluorescent imaging guided PDT applications.

High-Performance D-A Copolymer Donor Based on Difluoroquinoxaline A-Unit with Alkyl-Chlorothiophene Substituents for Polymer Solar Cells

Side chain engineering with fluorine substitution is widely used to enhance photovoltaic performance of polymer donors in the research field of polymer solar cells(PSCs).However,fluorine substitution has disadvantages of complicated synthesis and high cost.Herein,we synthesized a novel D-A copolymer donor PBQ9 based on difluoroquinoxaline A-unit with chlorine substitution on its alkyl-thiophene side chains instead of fluorine substitution in the polymer donor PBQ6,which greatly shortens the synthetic route and reduces the cost.Interestingly,the optimized binary PSC with PBQ9 as polymer donor and m-TEH as acceptor demonstrated a high power conversion efficiency(PCE)of 18.81%(certified PCE of 18.33%by National Institute of Metrology,China)with a high fill factor of 80.59%,and the photovoltaic performance of the PSCs is insensitive to the different batches of the polymer donor.The results indicate that PBQ9 is a high-performance polymer donor and that chlorine substitution is an effective strategy to improve photovoltaic performance and reduce the cost of polymer donors.

n-Type Semiconductive Polymers Based on Pyrene-1,5,6,10-Tetracarboxyl Diimide

Donor-acceptor(D-A)conjugated polymers comprising electron-deficient aromatic dicarboximide units represent an important type of organic semiconductors,especially for electron transporting properties.Pyrene-1,5,6,10-tetracarboxyl diimide(PyDI),a new PAH dicarboximide molecule recently reported by us,provides a fine balance between the electron-stabilizing ability andπ-stacking tendency,as compared to the naphthalenediimide(NDI)and perylenediimide(PDI)analogues.In this study,using thienylene-vinylene-thienylene(TVT)and biselenophene(BS)as the electron donating comonomer,along with PyDI as the acceptor moiety,we develop two new D-A type conjugated polymers,which exhibit impressive electron-transporting performance.Specifically,in the solution-processed OFET devices,electron mobility of 0.18 and 0.20 cm^(2)·V^(−1)·s^(−1) are achieved with these polymers,respectively.Such findings further prove the optimal potential of PyDI for application as an electron-acceptor building block in the development of polymeric n-type semiconductors among all various high-performance functional D-A polymers.

Tuning Acceptor Length in Photocatalytic Donor-Acceptor Conjugated Polymers for Efficient Solar-to-Hydrogen Energy Conversion

The development of conjugated polymer photocatalysts for efficient solar-to-hydrogen energy conversion is highly desirable for the sustainability of our society.Although the construction of donor-acceptor(D-A)structure in conjugated polymer photocatalysts for solar-to-hydrogen energy conversion has been well documented,less attention has been paid on how large D and how large A units combined together could achieve the best performance.Herein,a series of D-A copolymers P(BDT-DBTSOx)(x=7,19,39,and 79)composed of a benzodithiophene(BDT)donor unit and an oligomeric dibenzo[b,d]thiophene sulfone(DBTSO)acceptor segment were synthesized and studied.It was found that the polymer photocatalytic stabilities under full-arc irradiation improved upon shortening the length of the acceptor segment.Under visible light irradiation and in the presence of 3 wt%Pt cocatalyst,P(BDT-DBTSO79)displayed the best performance with an optimal hydrogen evolution rate of 119.3±5.8 mmol·g^(-1)·h^(-1).This is 1.4-fold as that of DBTSO homopolymer and 22.5-fold as that of BDT/DBTSO alternative copolymer,highlighting the importance of acceptor length in D-A structure for achieving high photocatalytic performance.

Embedding pyridine units in acceptors to construct donor-acceptor conjugated polymers

The development of donor-acceptor(D-A) conjugated polymers greatly promotes the device performance in organic electronics. Recently, the strategy of embedding pyridine units into D-A conjugated polymer backbones has attracted much attention due to the resulted lowered LUMO levels. In addition, the possible non-bonding interactions resulted from the nitrogen atoms also improve the coplanarity of the polymer backbones. All these factors have great contribution to enhance the device performance. In this review, we summarized the recent development of pyridine-embedded D-A conjugated polymers and their applications in organic field-effect transistors(OFETs).

Donor-Acceptor Oligomers and Polymers Composed of Benzothiadiazole and 3-Hexylthiophene： Effect of Chain Length and Regioregularity

A series of donor-acceptor oligomer OBTThn （n = 1- 7） and polymer PBTThl and PBTTh2 composed of al- ternative 2,1,3-benzothiadiazole and 3-hexylthiophene have been designed and synthesized for the purpose of in- vestigation on the effect of chain length and side-chain regioregularity on their basic properties and photovoltaic performance. In the OBTThn oligomers and PBTThl polymer, all the hexyl side chains on thienyl units orient to- ward the same direction. Upon elongation of the chain length, the intramolecular charge transfer （ICT） absorption band in solution gradually redshifts from 398 nm for OBTThl to 505 nm for OBTThT, then to 512 nm for PBTThl polymer. Meanwhile, the HOMO energy level increases from -5.45 eV （OBTTh0 to -5.08 eV （OBTThT） and -5.09 eV （PBTThl）, and the LUMO energy level decreases from -3.11 eV （OBTTh0 to -3.30 eV （OBTThT） and -3.33 eV （PBTThl）, thus giving a smaller and smaller energy bandgap for higher oligomers and polymers. Theo- retical calculation suggests straight line-like backbone geometry for this series of oligomers and polymer. On the other hand, polymer PBTTh2 possesses a different side-chain regioregularity, in which every two neighbor hexyl side chains are arranged in different orienting direction. It is theoretically suggested to have curved line-like back- bone geometry. In solution, it shows similar photophysical and electrochemical properties as PBTThl. However in film state, it displays a less redshift in the ICT band as refer to that in solution than PBTThl. In combination with [6,6]-phenyl-C61-butyric acid methyl ester （PC61BM）, these oligomers and polymers were used as donor material to fabricate organic bulk heterojunction solar cells. Again, chain length-dependent device photovoltaic performance was observed. The device based on OBTTh4 showed a power conversion efficiency of 0.16%, while it increased to 0.36% and 0.49% for the devices based on OBTTh6 and PBTThb respectively. However, the side-chain regio- regularity has less influence on the device photovoltaic output since the device based on PBTTh~ displayed an effi- ciency of 0.52%, comparable to that of PBTThl.

Largeπ-extended donor-acceptor polymers for highly efficient in vivo near-infrared photoacoustic imaging and photothermal tumor therapy

Semiconducting polymers(SPs)with intensive near-infrared(NIR)absorption and high photothermal conversion efficiencies have been employed as a new generation of photothermal agents(PTAs)for“all-in-one”theranostic nanoplatforms with integrated photoacoustic imaging(PAI)and photothermal therapy(PTT)functions.However,the lack of facile molecular design principles impedes the development of highly efficient NIR PTAs.Herein,a facile molecular design strategy based on largeπ-extended donor-acceptor(L-π-D-A)structure is reported for achieving SPs(SP1-SP3)with highly efficient in vitro and in vivo PAI and PTT capabilities.Through adjusting the conjugation length and planarity of the donor units,both SP3 and corresponding nanoparticle(SPN)SPN3 exhibit stronger D-A strength,intensive NIR absorption,enhanced absorption coefficient,and higher photothermal conversion efficiency(up to 61.8%).The excellent photothermal conversion efficiencies make SPN1-SPN3 produce efficient inhibition of tumor growth with excellent biocompatibility and prominent PAI performance with a high contrast manner in living mice at a low systemic injection mass.Our research highlights that the new L-π-D-A molecular design is an effective strategy to obtain highly efficient polymeric NIR PTAs for high desirable cancer phototheranostic nanoplatforms.

D-A Copolymers Based on a Pentacyclic Acceptor Unit and a 3,3′-Difluoro-2,2′-bithiophene for Solar Cells

A D-A copolymer, P2FBTTPTI, was developed by copolymerizing a pentacyclic acceptor unit, thieno[2′,3′：5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11（4 H,10 H）-dione（TPTI）, with 3,3′-difluoro-2,2′-bithiophene（2 FBT）. P2 FBTTPTI possessed a low highest occupied molecular orbital（HOMO） energy level（-5.50 e V） and a good hole mobility（4.14 × 10^-4 cm^2·V^-1·s^-1）. P2FBTTPTI：PC_（71）BM solar cells gave a decent power conversion efficiency（PCE） of 7.64% and a high open-circuit voltage（Voc） of 0.95 V.

Effect of furan π-bridge on the photovoltaic performance of D-A copolymers based on bi(alkylthio-thienyl)benzodithiophene and fluorobenzotriazole

The medium band gap donor-acceptor （D-A） copolymer J61 based on bi（alkylthio-thienyl）benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit and thiophene as n-bridge has demonstrated excellent photovoltaic performance as donor material in nonfullerene polymer solar cells （PSCs） with narrow bandgap n-type organic semiconductor ITIC as acceptor. For studying the effect of n-bridges on the photovoltaic performance of the D-A copolymers, here we synthesized a new D-A copolymer J61-F based on the same donor and acceptor units as J61 but with furan n-bridges instead of thiophene. J61-F possesses a deeper the highest occupied molecular orbital （HOMO） level at -5.45 eV in comparison with that （-5.32 eV） of J61. The non-fullerene PSCs based on J61-F：ITIC exhibited a maximum power conversion efficiency （PCE） of 8.24% with a higher open-circuit voltage （Voc） of 0.95 V, which is benefitted from the lower-lying HOMO energy level of J61-F donor material. The results indicate that main chain engineering by changing n-bridges is another effective way to tune the electronic energy levels of the conjugated D-A copolymers for the application as donor materials in non-fullerene PSCs.

Zinc-coordination Polymers Based on a Donor-acceptor Mix-ligand System:Syntheses,Crystal Structures and Photophysical Properties

By employing an electron-rich tricarboxytriphenyl amine as donor ligand and electron-deficient 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine as acceptor ligand to assemble with Zn2+ions,three new coordination polymers were successfully synthesized and characterized systematically.Three compounds with different structures were obtained by regulating the reaction solvent,and the effect of the reaction solvent on the synthesis of crystals was explored.Furthermore,the photophysical properties of the compounds were investigated.

Donor-acceptor covalent organic frameworks-confined ultrafine bimetallic Pt-based nanoclusters for enhanced photocatalytic H_(2)generation

Photocatalytic hydrogen generation from hydrogen storage media is an effective and promising approach for the green hydrogen industry as well as for achieving carbon neutrality goals.However,the lower photocatalytic efficiency due to the limited light trapping capacity,low electron transfer rate,and severe aggregation of nanoparticles caused by high surface energy seriously restricts their practical application.Herein,we constructed a series of donor–acceptor(D–A)type covalent organic frameworks to confine ultrafine bimetallic Pt-based nanoclusters for photocatalytic hydrogen generation from ammonia borane(AB)hydrolysis.Under visible light irradiation at 20℃,PtCo_(2)@covalent organic framework(COF)showed the highest photocatalytic activity with a turnover frequency(TOF)of 486 min−1.Experiments and density functional theory(DFT)calculations reveal that the high catalytic activity is mainly attributed to the strong electronic interactions between D–A type COF and ultrafine PtCo_(2)nanoclusters.Specifically,the D–A type COF can significantly enhance the light-trapping ability by fine-tuning the electron-acceptor type in the framework,and accelerate the photogenerated electron transfer from D–A type COF to PtCo_(2)nanocluster,which promotes the adsorption and activation of H_(2)O and AB molecules and accelerates hydrogen release.Furthermore,PtCo_(2)@COF also exhibited ultra-high durability due to the significantly enhanced resistance to nanocluster aggregation caused by the nanopore confinement effect of D–A type COF.We believe that this work will provide a theoretical guide for the rational design of efficient D–A COFbased catalysts for photocatalysis.

A new building block with intramolecular D-A character for conjugated polymers: ladder structure based on B←N unit

The general strategy to construct D-A type conjugated polymers is alternating copolymerization of electron-donating(D)monomer and electron-accepting(A)monomer.In this article,we report a new strategy to develop D-A type conjugated polymers,i.e.first fuse the D and A units into a polycyclic structure to produce a building block and then polymerize the building block with another unit.We develop a new building block with ladder structure based on B←N unit,B←N bridged dipyridylbenzene(BNDPB).In the skeleton of BNDPB,one diamine-substituted phenylene ring(D unit)and two B←N-linked pyridyl rings(A unit)are fused together to produce the polycyclic structure.Owning to the presence of intramolecular D-A character,the building block itself exhibits narrow bandgap of 1.74 eV.The conjugated polymers based on BNDPB show unique electronic structures,i.e.localized HOMOs and delocalized LUMOs,which are rarely observed for conventional D-A conjugated polymers.The polymers exhibit smaller bandgap than that of the building block BNDPB and display near-infrared(NIR)light absorption(λabs=ca.700 nm).This study thus provides not only a new strategy to design D-A conjugated polymers but also a new kind of building block with narrow bandgap.