Dye‐Incorporated Polynaphthalenediimide Acceptor for Additive‐Free High‐Performance All‐Polymer Solar Cells

All‐polymer solar cells (all‐PSCs) can offer unique advantages for applications in flexible devices, and naphthalene diimide (NDI)‐based polymer acceptors are the widely used polymer acceptors. However, their power conversion efficiency (PCE) still lags behind that of state‐of‐the‐art polymer solar cells, due to low light absorption, suboptimal energy levels and the strong aggregation of the NDI‐based polymer acceptor. Herein, a rhodanine‐based dye molecule was introduced into the NDI‐based polymer acceptor by simple random copolymerization and showed an improved light absorption coefficient, an up‐shifted lowest unoccupied molecular orbital level and reduced crystallization. Consequently, additive‐free all‐PSCs demonstrated a high PCE of 8.13 %, which is one of the highest performance characteristics reported for all‐PSCs to date. These results indicate that incorporating a dye into the n‐type polymer gives insight into the precise design of high‐performance polymer acceptors for all‐PSCs.     

Stimuli‐Responsive Self‐Assembly of a Naphthalene Diimide by Orthogonal Hydrogen Bonding and Its Coassembly with a Pyrene Derivative by a Pseudo‐Intramolecular Charge‐Transfer Interaction

A naphthalene diimide (NDI) building block containing hydrazide (H1) and hydroxy (H2) groups self‐assembled into a reverse‐vesicular structure in methylcyclohexane by orthogonal H‐bonding and π‐stacking. At an elevated temperature (LCST=43 °C), destruction of the assembled structure owing to selective dissociation of H2–H2 H bonding led to macroscopic precipitation. Further heating resulted in homogeneous redispersion of the sample at 70 °C (UCST) and the formation of a reverse‐micellar structure. In the presence of a pyridine (H3)‐functionalized pyrene (PY) donor, a supramolecular dyad (NDI–PY) was formed by H2–H3 H‐bonding. Slow transformation into an alternate NDI–PY stack occurred by a folding process due to the charge‐transfer interaction between NDI and PY. The mixed NDI–PY assembly exhibited a morphology transition from a reverse micelle (with a NDI–PY mixed‐stack core) below the LCST to another reverse micelle (with a NDI core) above the UCST via a “denatured” intermediate.     

Hydrogen‐Bonding‐Regulated Supramolecular Nanostructures and Impact on Multivalent Binding

Herein we describe the H‐bonding‐regulated nanostructure, thermodynamics, and multivalent binding of two bolaamphiphiles NDI‐1 and NDI‐2 consisting of a hydrophobic naphthalene diimide connected to a hydrophilic wedge by a H‐bonding group and a glucose moiety on its two arms. NDI‐1 and NDI‐2 differ by the single H‐bonding group, namely, hydrazide or amide, which triggers the formation of vesicles and cylindrical micelles, respectively. Although the extended H‐bonding ensures stacking with head‐to‐head orientation and the formation of an array of the appended glucose moieties in both systems, the adaptive cylindrical structure exhibited superior multivalent binding with concanavalin A (ConA) to that of the vesicle. A control amphiphile lacking a H‐bonding group assembled with a random lateral orientation to produce spherical micelles without any notable multivalent binding.     

Synthesis and characterization of arylenevinylenearylene–naphthalene diimide copolymers as acceptor in all–polymer solar cells

Two n‐type conjugated D‐A copolymers, P(TVT‐NDI) and P(FVF‐NDI) with thienylene‐vinylene‐thienylene (TVT) or furanylene‐vinylene‐furanylene (FVF) as donor (D) units and naphthalene diimide (NDI) as the acceptor (A) units, were synthesized by the Stille coupling copolymerization. The two polymers possess good solubility, high thermal stability, and broad absorption bands with absorption edges at 866 nm for P(TVT‐NDI) and 886 nm for P(FVF‐NDI) . The LUMO energy levels of P(TVT‐NDI) and P(FVF‐NDI) are ?3.80 eV and ?3.76 eV respectively, so the two polymers are suitable for the application as acceptor in blending with most polymer donor in PSCs based on the energy level matching point of view. All polymer solar cells (all‐PSCs) were fabricated with P(TVT‐NDI) or P(FVF‐NDI) as acceptor and medium bandgap polymer J51 as donor for investigating the photovoltaic performance of the two n‐type conjugated polymer acceptors. And higher power conversion efficiency of 6.43% for P(TVT‐NDI) and 5.21% for P(FVF‐NDI) was obtained. The results indicate that arylenevinylenearylene–naphthalene diimide copolymer are promising polymer acceptor for all–PSCs. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1757–1764     

Naphthalene‐Diimide‐Based Ionenes as Universal Interlayers for Efficient Organic Solar Cells

Self‐doping ionene polymers were efficiently synthesized by reacting functional naphthalene diimide (NDI) with 1,3‐dibromopropane ( NDI‐NI ) or trans‐1,4‐dibromo‐2‐butene ( NDI‐CI ) via quaternization polymerization. These NDI‐based ionene polymers are universal interlayers with random molecular orientation, boosting the efficiencies of fullerene‐based, non‐fullerene‐based, and ternary organic solar cells (OSCs) over a wide range of interlayer thicknesses, with a maximum efficiency of 16.9 %. NDI‐NI showed a higher interfacial dipole (Δ), conductivity, and electron mobility than NDI‐CI , affording solar cells with higher efficiencies. These polymers proved to efficiently lower the work function (WF) of air‐stable metals and optimize the contact between metal electrode and organic semiconductor, highlighting their power to overcome energy barriers of electron injection and extraction processes for efficient organic electronics.     

Direct C−H Arylation Meets Perovskite Solar Cells: Tin‐Free Synthesis Shortcut to High‐Performance Hole‐Transporting Materials

In contrast to the traditional multistep synthesis, we demonstrate herein a two‐step synthesis shortcut to triphenylamine‐based hole‐transporting materials (HTMs) through sequential direct C?H arylations. These hole‐transporting molecules are fabricated in perovskite‐based solar cells (PSCs) that exhibit promising efficiencies up to 17.69 %, which is comparable to PSCs utilizing commercially available 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (spiro‐OMeTAD) as the HTM. This is the first report describing the use of step‐saving C?H activations/arylations in the facile synthesis of small‐molecule HTMs for perovskite solar cells.     

Gated Electron Sharing Within Dynamic Naphthalene Diimide‐Based Oligorotaxanes

The controlled self‐assembly of well‐defined and spatially ordered π‐systems has attracted considerable interest because of their potential applications in organic electronics. An important contemporary pursuit relates to the investigation of charge transport across noncovalently coupled components in a stepwise fashion. Dynamic oligorotaxanes, prepared by template‐directed methods, provide a scaffold for directing the construction of monodisperse one‐dimensional assemblies in which the functional units communicate electronically through‐space by way of π‐orbital interactions. Reported herein is a series of oligorotaxanes containing one, two, three and four naphthalene diimide (NDI) redox‐active units, which have been shown by cyclic voltammetry, and by EPR and ENDOR spectroscopies, to share electrons across the NDI stacks. Thermally driven motions between the neighboring NDI units in the oligorotaxanes influence the passage of electrons through the NDI stacks in a manner reminiscent of the conformationally gated charge transfer observed in DNA.     

From‐Core and From‐End Direct CH Arylations: A Step‐Saving New Synthetic Route to Thieno[3,4‐c]pyrrole‐4,6‐dione (TPD)‐Incorporated D‐‐π–A–π–D Functional Oligoaryls

In contrast to the traditional multistep synthesis, herein an efficient and fewer‐steps new synthetic strategy is demonstrated for the facile preparation of organic‐electronically important D–π–A–π–D‐type oligoaryls through sequential direct C?H arylations. This methodology has shown that the synthesis of thieno[3,4‐c]pyrrole‐4,6‐dione (TPD)‐ or furano[3,4‐c]pyrrole‐4,6‐dione (FPD)‐centred target molecules could be accessed step‐economically either from the core structure (acceptor) or from the end structure (donor), which supplied a more flexible and succinct new synthetic alternative to the preparation of the π‐functional small‐molecule semiconducting materials. In addition, optical and electrochemical properties of the synthesized oligoaryls were examined.     

From Bola‐amphiphiles to Supra‐amphiphiles: The Transformation from Two‐Dimensional Nanosheets into One‐Dimensional Nanofibers with Tunable‐Packing Fashion of n‐Type Chromophores

With a rational design of the supra‐amphiphiles, we have successfully demonstrated that not only the dimension of the self‐assembled nanostructures, but also the packing fashion of the functional naphthalene diimide (a typical n‐type chromophore), can be tuned in a noncovalent way in aqueous solution. Naphthalene diimide is incorporated into a bola‐amphiphile as the rigid core, whereas viologen derivatives are used as the hydrophilic head. The bola‐amphiphile self‐assembles into two‐dimensional nanosheets, in which naphthalene diimide adopts a “J‐type” aggregation. Water‐soluble supramolecular complexation between viologen derivatives and the 8‐hydroxypyrene‐1, 3, 6‐trisulfonic acid trisodium salt is used as a driving force for the formation of the supra‐amphiphiles. Upon formation of the supra‐amphiphiles, the nanosheets transform into ultralong nanofibers with a close packing of naphthalene diimide. Notably, just by mixing the two building blocks of the supra‐amphiphiles in aqueous solution, a dimension‐controlled evolution of the nanostructures is formed that leads to a different packing fashion of the n‐type functional chromophores, which is facile and environmental friendly.     

Hydrogen‐Bond‐Regulated Distinct Functional‐Group Display at the Inner and Outer Wall of Vesicles

A unique supramolecular strategy enables the unidirectional assembly of two bola‐shaped unsymmetric π‐amphiphiles, NDI‐1 and NDI‐2, which feature a naphthalene–diimide chromophore connected to nonionic and anionic head groups on opposite arms. The amphiphiles differ only in the location of a hydrazide group, which is placed either on the nonionic or on the anionic arm of NDI‐1 and NDI‐2, respectively. The formation of hydrogen bonds between the hydrazides, which compensates for electrostatic and steric factors, promotes unidirectional alignment and the formation of monolayer vesicles. The zeta potentials and cation‐assisted quantitative precipitation reveal negatively charged and nonionic outer surfaces for NDI‐1 and NDI‐2, respectively, indicating that hydrogen bonding also dictates the directionality of the monolayer curvature, ensuring that in both cases, the hydrazides remain at the inner wall to benefit from stronger hydrogen bonding where they are in closer proximity. This is reflected in their different abilities to inhibit α‐chymotrypsin, which possesses a positively charged surface: NDI‐1 induced an inhibition of 80 % whereas hardly any inhibition was observed with NDI‐2.     

Tuning the frontier molecular orbital energy levels of n‐type conjugated copolymers by using angular‐shaped naphthalene tetracarboxylic diimides,and their use in all‐polymer solar cells with high open‐circuit voltages

An angular‐shaped naphthalene tetracarboxylic diimide (NDI) was designed and synthesized as a new building block for n‐type conjugated polymers to tune their energy levels. Three n‐type copolymers incorporating this angular‐shaped NDI as the acceptor moiety were obtained by Stille coupling reactions and had number average molecular weights of 18.7–73.0 kDa. All‐polymer bulk‐heterojunction solar cells made from blends of these polymers with poly(3‐hexylthiophene) gave a power conversion efficiency up to 0.32% and exhibited an open‐circuit voltage (V_oc) up to 0.94 V due to their relative high‐lying lowest unoccupied molecular orbital energy levels. The high V_oc of 0.94 V is higher than that of solar cells based on linear‐shaped NDI‐containing polymers (<0.6 V). The results indicate that the angular‐shaped NDI is a promising building block for constructing nonfullerene polymer acceptors for solar cells with high open‐circuit voltages. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and Photophysics of Core‐Substituted Naphthalene Diimides: Fluorophores for Single Molecule Applications

The synthesis and photophysics of two new aminopropenyl naphthalene diimide (SANDI) dyes are reported. A general and convenient method for the synthesis of the precursor mono‐, di‐, and tetrabrominated 1,4,5,8‐naphthalene tetracarboxylic dianhydrides is described. The two core‐substituted SANDIs exhibit many of the photophysical properties required for fluorescence labeling applications including high photostability and high fluorescence quantum yields (>0.5) in the visible region of the spectrum. The emission wavelength is sensitive to the number of substituents on the NDI core, and the fluorescence decay times are in the range of ～8–12 ns for both compounds in the solvents investigated. Preliminary fluorescence emission data from single molecules of the compounds embedded in poly(methyl methacrylate) films are also reported and show that single molecules have very low yields of photobleaching, particularly the di‐substituted system. Furthermore, only a small proportion (<10 %) of the single molecules studied display fluorescence intermittencies or “blinks” in their photon trajectory. The compounds appear to be excellent candidates for applications at the single molecule level, for example, as FRET labels.     

Autoresolution of Segregated and Mixed p‐n Stacks by Stereoselective Supramolecular Polymerization in Solution

A “chirality driven self‐sorting” strategy is introduced for the controlled supramolecular organization of donor (D) and acceptor (A) molecules in multicomponent assemblies. The trans‐1,2‐bis(amido)cyclohexane (trans‐BAC) has been identified as a supramolecular motif with strong homochiral recognition to direct this chirality controlled assembly process of enantiomers in solution. Stereoselective supramolecular polymerization of trans‐BAC appended naphthalene diimide monomers (NDIs) has been probed in detail by spectroscopic and mechanistic investigations. This chirality‐driven self‐sorting design of enantiomeric components also offers to realize mixed and segregated D‐A stacks by supramolecular co‐assembly of the NDI acceptors with trans‐BAC appended dialkoxynaphthalene (DAN) donor monomers. Such an unprecedented chirality control on D‐A organization paves the way for the creation of supramolecular p‐n nanostructures with controlled molecular‐level organization.     

Folding of a Donor‐Containing Ionene by Intercalation with an Acceptor

Cationic ionenes that bear electron‐rich 1,5‐dialkoxynaphthalene (DAN) units within the alkylene segment were allowed to interact with different types of electron‐deficient, acceptor‐containing molecules in an effort to realize intercalation‐induced folding of the ionenes; the collapse of the chains was expected to occur in such a way that the donor and acceptor units become arranged in an alternating fashion. Several acceptor‐bearing molecules were prepared by the derivatization of pyromellitic dianhydride and naphthalene tetracarboxylic dianhydride with two different oligoethylene glycol monomethyl ether monoamines. This yielded acceptor molecules with different water solubility and allowed the examination of solvophobic effects in the folding process. UV/Vis spectroscopic studies were carried out by using a 1:1 mixture of the DAN–ionenes and different acceptor molecules in water/DMSO solvent mixtures. The intensity of the charge‐transfer (CT) band was seen to increase with the water content in the solvent mixture, thereby suggesting that the intercalation is indeed aided by solvophobic effects. The naphthalene diimide (NDI) bearing acceptor molecules consistently formed significantly stronger CT complexes when compared to the pyromellitic diimide (PDI) bearing acceptor molecules, which is a reflection of the stronger π‐stacking tendency of the former. AFM studies of drop‐cast films of different ionene–acceptor combinations revealed that compact folded structures are formed most effectively under conditions in which the strongest CT complex is formed.     

Side chain engineering of naphthalene diimide–bithiophene‐based polymer acceptors in all‐polymer solar cells

Two novel polymeric acceptors based on naphthalene diimide (NDI) and 2.2′‐bithiophene, named as P(NDI2THD‐T2) and P(NDI2TOD‐T2), were designed and synthesized for all polymer solar cells application. The structural and electronic properties of the two acceptors were modulated through side‐chain engineering of the NDI units. The optoelectronic properties of the polymers and the morphologies of the blend films composed of the polymer acceptors and a donor polymer PTB7‐Th were systemically investigated. With thiophene groups introduced into the side chains of the NDI units, both polymers showed wider absorption from 350 nm to 900 nm, compared with the reference polymer acceptor of N2200. No redshift of absorption spectra from solutions to films indicated reduced aggregation of the polymers due to the steric hindrance effect of thiophene rings in the side chains. The photovoltaic performance were characterized for devices in a configuration of ITO/PEDOT:PSS/PTB7‐Th:acceptors/2,9‐bis(3‐(dimethylamino)propyl)anthra[2,1,9‐def:6,5,10‐def]diisoquinoline‐1,3,8,10(2H,9H)‐tetraone (PDIN)/Al. With the addition of diphenyl ether as an additive, the power conversion efficiencies (PCEs) of 2.73% and 4.75% for P(NDI2THD‐T2) and P(NDI2TOD‐T2) based devices were achieved, respectively. The latter showed improved J_sc, Fill Factor (FF), and PCE compared with N2200 based devices. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3679–3689     

n‐Type Conjugated Polymer Based on Dicyanodistyrylbenzene and Naphthalene Diimide Units for All‐Polymer Solar Cells

All polymer solar cells (all‐PSCs), possessing superior mechanical strength and flexibility, offer the commercialization opportunity of the PSCs for flexible and portable devices. In this work, we designed and synthesized two copolymer acceptors based on dicyanodistyrylbenzene (DCB) and naphthalene diimide (NDI) units. The corresponding copolymer acceptors are denoted as PDCB‐NDI812 and PDCB‐NDI1014. The medium band gap copolymer PBDB‐T was selected as donor material for investigation of the photovoltaic performance. Two all‐PSCs devices showed power conversion efficiencies (PCE) of 4.26% and 3.43% for PDCB‐NDI812 and PDCB‐NDI1014, respectively. The improved PCE was ascribed to the higher short‐circuit current (J_SC), greater charge carrier mobility and higher exciton dissociation probability of the PBDB‐T:PDCB‐NDI812 blend film. These results suggest that DCB unit and NDI unit based copolymer acceptors are promising candidates for high performance all‐PSCs.     

Synthesis of Phenalenyl‐Fused Pyrylium Cations: Divergent C−H Activation/Annulation Reaction Sequence of Naphthalene Aldehydes with Alkynes

Described herein is the synthesis of stable oxonium‐doped polycyclic aromatic hydrocarbons (PAHs) by the rhodium‐catalyzed C−H activation/annulations of naphthalene‐type aldehydes with internal alkynes. This protocol provides four divergent reaction types, including two unexpected annulations with an oxygen transposition process, which lead to diverse types of phenalenyl‐fused pyrylium cations comprising a four‐, five‐, or six‐ring‐fused π‐conjugated core. The annulations exhibit an exquisite regioselectivity and a high tolerance of sensitive functional groups. These PAHs feature intriguing photophysical properties such as full‐color tunable fluorescence emission, high quantum yield, and positively charged core, and can be reduced easily to the phenalenyl radicals.     

One donor–two acceptor (D–A1)‐(D–A2) random terpolymers containing perylene diimide,naphthalene diimide,and carbazole units

A series of one donor–two acceptor (D–A₁)‐(D–A₂) random terpolymers containing a 2,7‐carbazole donor and varying compositions of perylene diimide (PDI) and naphthalene diimide (NDI) acceptors was synthesized via Suzuki coupling polymerization. The optical properties of the terpolymers are weighted sums of the constituent parent copolymers and all show strong absorption over the 400 to 700 nm range with optical bandgaps ranging from 1.77 to 1.87 eV, depending on acceptor composition. The copolymers were tested as acceptor materials in bulk heterojunction all‐polymer solar cells using poly[(4,8‐bis‐(2‐ethylhexyloxy)‐benzo[1,2‐b;4,5‐b′]dithiophene)‐2,6‐diyl‐alt‐(4‐(2‐ethylhexanoyl)‐thieno[3,4‐b]thiophene)‐2,6‐diyl] (PBDTTT‐C) as the donor material. In contrast to the optoelectronic properties, the measured device parameters are not composition dependent, and rather depend solely on the presence of the NDI unit, where the devices containing any amount of NDI perform half as well as those using the parent polymer containing only carbazole and PDI. Overall this is the first example of a one donor–two acceptor random terpolymer system containing perylene diimide (PDI) and naphthalene diimide (NDI) acceptor units, and demonstrates a facile method of tuning polymer optoelectronic properties while minimizing the need for complicated synthetic and purification steps. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3337–3345     

Visualization of Stereoselective Supramolecular Polymers by Chirality‐Controlled Energy Transfer

Chirality‐driven self‐sorting is envisaged to efficiently control functional properties in supramolecular materials. However, the challenge arises because of a lack of analytical methods to directly monitor the enantioselectivity of the resulting supramolecular assemblies. Presented herein are two fluorescent core‐substituted naphthalene‐diimide‐based donor and acceptor molecules with minimal structural mismatch and they comprise strong self‐recognizing chiral motifs to determine the self‐sorting process. As a consequence, stereoselective supramolecular polymerization with an unprecedented chirality control over energy transfer has been achieved. This chirality‐controlled energy transfer has been further exploited as an efficient probe to visualize microscopically the chirality driven self‐sorting.     

Axially Chiral Dibenzazepinones by a Palladium(0)‐Catalyzed Atropo‐enantioselective C−H Arylation

Atropo‐enantioselective C?H functionalization reactions are largely limited to the dynamic kinetic resolution of biaryl substrates through the introduction of steric bulk proximal to the axis of chirality. Reported herein is a highly atropo‐enantioselective palladium(0)‐catalyzed methodology that forges the axis of chirality during the C?H functionalization process, enabling the synthesis of axially chiral dibenzazepinones. Computational investigations support experimentally determined racemization barriers, while also indicating C?H functionalization proceeds by an enantio‐determining CMD to yield configurationally stable eight‐membered palladacycles.