Article

Post-polymerization Modification of Phosphorus Containing Conjugated Copolymers

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Abstract

A new phosphafluorene (PF) based monomer, featuring a phosphine oxide substituted with a dodecyl chain, was synthesized. PF was copolymerized with benzodithiophene (BDTT) to form the copolymer PPF-BDTT which has a donor (BDTT)–acceptor (PF) structure. For the first time, direct post-polymerization modifications were performed on the phosphorus center of phosphafluorene-containing conjugated polymers. With Lawesson's Reagent, PPF-BDTT was transformed from a phosphine oxide to a phosphine sulfide. Reduction of the phosphine oxide of PPF-BDTT with HSiCl3, followed by reaction with AuCl∙SMe2, produced PPF-BDTT-Au, which contains AuCl coordinated to the phosphafluorene moiety. PPF-BDTT, PPF-BDTT-S, and PPF-BDTT-Au were characterized optically and electrochemically and the results compared to related BDTT containing copolymers. PPF-BDTT and its derivatives were found to have high LUMO and HOMO levels and larger bandgaps compared to common donor-acceptor copolymers. Organic solar cells were fabricated from PPF-BDTT, PPF-BDTT-S, and PPF-BDTT-Au, although the performances of these devices were poor with power conversion efficiencies ranging from 0.13% to 0.60%.

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... 87,88 In a different approach, Rupar and colleagues reported the post-polymerisation modification of phosphafluorene oxide-containing copolymers (Fig. 13). 89 The initially prepared donor-acceptor type copolymer P32 could undergo three different modifications at the phosphorus centre: (i) reduction of the P-centre with HSiCl 3 , although the resulting polymer rapid re-oxidized in presence of air, (ii) quantitative reduction and coordination to a transition metal such as gold (AuCl), enabling air-stability of the resulting polymer P33, and (iii) quantitative conversion of the phosphine oxide to phosphine sulfide with Lawesson's reagent, giving polymer P34. Gold complexation resulted in a significant change in optical and electronic properties, compared to the parent P32, whereas changing the phosphine oxide to the phosphine sulfide had a more subtle effect (Table 4). ...
... Modification of phosphafluorene oxide-containing polymer P32.89 ...
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Changes in color are one of the most obvious and easily followed responses that can be induced by an external stimulus. π-Conjugated organophosphorus compounds are on the rise to challenge established systems by opening up new and simple pathways to diversely modified optoelectronic properties - the main challenge for the development of new chromic materials. Relevant stimuli highlighted in this Frontier article include electronic current (electrochromism), light (photochromism), solvent polarity (solvatochromism), aggregation formation (aggregation induced emission, AIE), mechanical force (mechanochromism), temperature (thermochromism), organic solvent vapor (vapochromism), and pH (halochromism).
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The study emphasizes the correlation between chemical structures, physical properties, and resulting device performance of the solution-processed polymers/small molecules, and tries to provide a comprehensive understanding from materials design to a variety of device applications. To achieve near-IR absorbing/emitting abilities, strong donor-acceptor interaction and stabilization of the quinoid resonant structure are required. However, due to the smaller one-dimensional quantum well length, bandgap lowering is more difficult and normally requires very strong donor or acceptor units in the case of small molecules. Anthopoulos and Patil showed that the triethylene glycol side chain can enhance molecular self-assembly and increase the FET mobility for DPP-based polymers. Gong applied PS-TPD-PFCB, a commonly used electron-blocking material in light-emitting diodes, in a novel IR photodetector and realized very low dark current and high detection sensitivity. Yang and Li's recent work shows a clear link between the polymers' molecular compatibility (preferred orientations) and the resulting multidonor system morphology, which has a profound impact on the carrier transport and device efficiency.
Article
The electronic properties of materials targeted for N-type organic field-effect transistors (OFETS), such as pyromellitic diimides (PyDIs), degrade under ambient conditions because of low susceptibility of radical anions. To improve the electronic properties of PyDIs, we synthesized two PyDI analogs by imidization of pyromellitic dianhydride with different amines and thionated them with Lawesson’s reagent in toluene. Thin films of the parent and derivative compounds were then deposited onto Si/SiO2 substrates as prototype OFETs. Thionation and fluorination increased the electron mobility and on/off ratio of the original diimides by two orders of magnitude and improved the threshold voltage and air-stability of diimide compounds. Our derived compounds are expected to realize air-stable N-type OFETs for large-area and flexible electronics
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We report a new multi-functional copolymer, PDTP-DTBDT containing DTP and DTBDT units. Surprisingly, the introduction of novel DTP and DTBDT units bring not only superior charge transfer properites but also charge transport characteristics for efficient bulk heterojunction solar cells.
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Two novel semiconducting polymers based on benzodithiophene and dithienophosphole oxide (DTP) units are designed and synthesized. A novel electron-deficient DTP moiety is developed. Surprisingly, the introduction of DTP units brings highly polarizable characteristics, which is beneficial for the photocurrent in solar cells. Thus, the donor–acceptor type of conjugated polymers based on this novel acceptor has superior charge transfer properties and highly efficient PL quenching efficiencies. As a result, polymer solar cells (PSCs) with high power conversion efficiencies of 6.10% and 7.08% are obtained from poly(3,5-didodecyl-4-phenylphospholo[3,2-b:4,5-b']dithiophene–4-oxide-alt-4,8-bis(5-decylthiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene) (PDTP–BDTT) and PDTP–4-oxide-alt-4,8-bis(5-decylselenophen-2-yl)benzo[1,2-b:4,5-b']dithiophene) (PDTP–BDTSe), respectively, when the photoactive layer is processed with the 1,8-octanedithiol (ODT) additive. The PDTP–BDTSe copolymer is now the best performing DTP-based material for PSCs. Using the polarizable unit strategy determined in this study for the molecular design of conjugated polymers is expected to greatly advance the development of organic electronic devices.
Article
A series of isoindigo-based conjugated polymers (PII2F-CmSi, m = 3–11) with alkyl siloxane-terminated side chains are prepared, in which the branching point is systematically “moved away” from the conjugated backbone by one carbon atom. To investigate the structure–property relationship, the polymer thin film is subsequently tested in top-contact field-effect transistors, and further characterized by both grazing incidence X-ray diffraction and atomic force microscopy. Hole mobilities over 1 cm2 V−1 s−1 is exhibited for all soluble PII2F-CmSi (m = 5–11) polymers, which is 10 times higher than the reference polymer with same polymer backbone. PII2F-C9Si shows the highest mobility of 4.8 cm2 V−1 s−1, even though PII2F-C11Si exhibits the smallest π–π stacking distance at 3.379 Å. In specific, when the branching point is at, or beyond, the third carbon atoms, the contribution to charge transport arising from π–π stacking distance shortening becomes less significant. Other factors, such as thin-film microstructure, crystallinity, domain size, become more important in affecting the resulting device's charge transport.
Article
A substituted poly(9-borafluorene) (P9BF) homopolymer, a boron congener of polyfluorene, is prepared by Yamamoto coupling of a triisopropylphenyl substituted borafluorene (1). As predicted by prior density functional theory (DFT) studies, P9BF has a reduced optical bandgap (Eg,opt = 2.28 eV) and a significantly lowered LUMO level (-3.9 eV, estimated by cyclic voltammetry (CV)) compared to polyfluorene. In addition to binding fluoride in solution, films of P9BF exhibit a reversible, simultaneous turn-off/turn-on fluorescence response to NH3 vapor. A 9-borafluorene-vinylene copolymer (P9BFV) is synthesized via Stille coupling, demonstrating that 1 can readily be incorporated into copolymers. The extended conjugation of P9BFV due to the inclusion of the vinylene group results in a reduced optical bandgap (2.12 eV) and LUMO (-4.0 eV, estimated by CV) compared to the homopolymer P9BF. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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A study was conducted to examine the syntheses and properties of oligomers and polymers based on fused thiophenes, such as thienothiophenes, dithienothiophenes, and thienoacenes made up exclusively of two or more thiophenes, along with their applications. A modified approach was applied to synthesize 3-hydroxythieno[3,2-b]thiophene from 3-bromothiophene. Formation of 3-lithiothiophene was followed by addition of elemental sulfur and α-chloroacetic acid to obtain the carboxylic acid which under hot acidic conditions formed 3-hydroxythieno[3,2-b]thiophene.
Article
We present synthesis and characteristics of the conjugated polymers involving organogallium complexes. A series of alternating copolymers composed of gallafluorene were prepared with diverse comonomers through various types of cross-coupling reactions such as Suzuki-Miyaura, Sonogashira-Hagihara, and Stille reactions. It was confirmed that the synthesized polymers possess solubility in common organic solvents and stability toward air and moisture. Significantly, optical properties originating from the electronic interaction between gallafluorene and various comonomers were observed. For example, vivid color emissions were demonstrated in the blue, green, yellow, orange, and red regions depending on the chemical structures of the comonomer units. In addition, it was eventually found that the benzotriazole-containing polymer showed significant optical properties originating from aggregation in the film state. From the electrochemical measurements, it was indicated that the energy levels of their frontier orbitals were varied by the comonomer units. Indeed, it is supported that the gallafluorene polymers have higher energy levels of HOMOs (highest occupied molecular orbitals) than those of the fluorene-based conjugated polymers instead of gallafluorene. Finally, it is suggested that the gallafluorene unit could work as an electron-donating group in the polymer main chain.
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We report the synthesis of dithienobenzotropone-based conjugated alternating copolymers by direct arylation polycondensation. Postpolymerization modification by hydride reduction yields cross-conjugated, reactive hydroxyl-containing copolymers that undergo phosphorylation and ionization upon exposure to the chemical warfare agent mimic diethylchlorophosphate (DCP). The resulting conjugated, cationic copolymer is highly colored and facilitates the spectroscopic and colorimetric detection of DCP in both solution and thin-film measurements.
Article
A new class of biselenophene-based materials including an sp(3)-silicon-bridged diselenosilole (DSS), an sp(3)-germanium-bridged diselenogermole (DSG), and an sp(3)-nitrogen-bridged diselenopyrrole (DSP) as well as an sp(2)-vinylidene-bridged dicyanodiselenofulvene (CDSF), a diacetylenediselenofulvene (ADSF), and a dioctylethylene-bridged benzodiselenophene (BDS) have been successfully synthesized and characterized. The bridging moieties play an important role in determining the optical and electrochemical properties. The six brominated derivatives are ready to construct various biselenophene-based conjugated materials with tunable properties for organic photovoltaics and field effect transistors.
Article
A series of low-bandgap alternating copolymers of dithienosilole and thienopyrrolodione (PDTSTPDs) are prepared to investigate the effects of the polymer molecular weight and the alkyl chain length of the thienopyrrole-4,6-dione (TPD) unit on the photovoltaic performance. High-molecular-weight PDTSTPD leads to a higher hole mobility, lower device series resistance, a larger fill factor, and a higher photocurrent in PDTSTPD:[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) bulk-heterojunction solar cells. Different side-chain lengths show a significant impact on the interchain packing between polymers and affect the blend film morphology due to different solubilities. A high power conversion efficiency of 7.5% is achieved for a solar cell with a 1.0 cm2 active area, along with a maximum external quantum efficiency (EQE) of 63% in the red region.
Article
A series of polymers containing benzo[1,2-b:4,5-b′]dithiophene and N-alkylthieno[3,4-c]pyrrole-4,6-dione are designed. By incorporating different alkylthienyl side chains, the fill factor (FF) and open circuit voltage (Voc) of the copolymers are further improved. The experimental results and theoretical calculations show that the size and topology of the side chains can influence the polymer solubility, energy levels, and intermolecular packing by altering the molecular coplanarity. As a result of improved morphology and fine-tuned energy levels, an increased FF and a high Voc of 1.00 V are achieved, as well as a power conversion efficiency of 6.17%, which is the highest efficiency ever reported for polymer solar cells with a Voc over 1 V.
Article
The development of conjugated organic materials has become a rapidly evolving field of research, particularly with a view toward practical applications in so-called organic electronics that encompass a variety of device types, such as OLEDs, OPVs, and OFETs. Almost all of these devices minimally require the presence of electron-donor and -acceptor components that act as p- and n-type semiconductors, respectively. Research over the past two decades has shown that while there is an abundant resource of organic p-type materials, suitable n-type species are few and far between. To overcome this severe bottleneck for the further development of organic electronics, researchers have identified organo-main-group avenues as valuable alternatives toward organic electron-acceptor materials that may ultimately be used as n-type components in practical devices. One particular element of interest in this context is phosphorus, which at first glance may not necessarily suggest such properties.
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In this study, we report the investigation of the influence of molecular weight (MW) on power conversion efficiency (PCE) of bulk heterojunction (BHJ) polymer solar cells (PSCs). It was found that PCEs of PSCs fabricated by poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) blended with [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) as the active layer, are significantly enhanced from 5.41% to 6.27% and 8.50% along with the MW of PTB7 increased from 18 kg/mol to 40 kg/mol and 128 kg/mol, respectively. This enhancement is attributed to the enhanced light absorption and increased charge carrier mobility of PTB7 with high MW, and a proper phase separation in BHJ composite of PTB7:PC71BM interpenetrating network. All these results demonstrate that the MW of donor polymer plays an important role in the performance of BHJ PSCs.
Article
(Phosp)hole in one: A palladium-catalyzed synthesis for directly assembling phosphole skeletons from triarylphosphines through CH and CP bond cleavage was developed. This approach overcomes several of the limitations of the so far reported methods. Phospholes bearing a range of functionalities (including Br, F, CO2 Me, Ac, and CN) and an array of fused rings (naphthalenes, anthracenes, furans, and pyrroles) can be easily synthesized.
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Inspired by the self‐assembled bilayer structures of natural amphiphilic phospholipids, a new class of highly luminescent “click”‐phospholes with exocyclic alkynyl group at the phosphorus center is reported. These molecules can be easily functionalized with a self‐assembly group to generate neutral “phosphole‐lipids”. This novel approach retains the versatile reactivity of the phosphorus center, allowing further engineering of the photophysical and self‐assembly properties of the materials at a molecular level. The results of this study highlight the importance of being able to balance weak intermolecular interactions for controlling the self‐assembly properties of soft materials. Only molecules with the appropriate set of intermolecular arrangement/interactions show both organogel and liquid crystal mesophases with well‐ordered microstructures. Moreover, an efficient energy transfer of the luminescent materials is demonstrated and applied in the detection of organic solvent vapors. The molecular engineering of novel “click”‐phospholes toward functional phosphole‐lipid soft materials is reported. Appropriate modification of the conjugated head group results in balanced intermolecular interactions and a tailored molecular arrangement that provides access to luminescent organogels and liquid crystals. Efficient energy transfer and vapochromism using one species are also demonstrated.
Article
With the rapid evolution of photovoltaic polymer materials, power conversion efficiency of polymer solar cells has been markedly improved in recent years, and is now approaching a landmark value of 10 %. This review focuses on Donor–Acceptor (D–A) photovoltaic copolymers. Starting from briefly introducing the D–A concept, the fundamental donor and acceptor units for constructing polymer photovoltaic materials are introduced and classified. By summarizing the structure–property relationships of typical photovoltaic D–A copolymers, the important design rules for such materials are highlighted. Several crucial aspects, including proper combination of D–A units, high planarity of the backbone and proper incorporation of side chains are particularly emphasized. A new D–A architecture, namely main-chain donor and side-chain acceptor is introduced and reviewed. Moreover, the role of the electron-deficient group in fine-tuning energy levels of low-bandgap D–A photovoltaic polymers is discussed.
Article
The single crystals of 9-phenyl-9-dibenzophosphole chalcogenides {oxide (1), sulfide (2) and selenide (3)} and a mixed crystal of 2 and 3 have been prepared and characterized by X-ray diffraction analysis. Several intermolecular interactions such as π–π and Se–H were observed in the mixed crystal of 2 and 3. The mixed crystal of 2 and 3 exhibited enhanced phosphorescence compared to the pure constituent crystal (2 or 3) at low temperature.
Article
A push in the right direction: An electron-accepting organophosphorus system has been combined with self-assembly features to create a strongly electron-accepting liquid-crystalline material. The stability and behavior of the self-assembled liquid crystal could be controlled by adjusting weak intermolecular forces, such as hydrogen bonding and π-π interactions.
Article
We present here a new derivative of poly-p-phenylene (PPP), the poly-2,8-indenofluorene (8a,b), to bridge the gap between 2,7-poly-9,9‘-dialkylfluorene (PF) (2) and ladder-poly-p-phenylene (LPPP) (4). The monomer 7a,b was synthesized starting from 6,12-dihydroindeno[1,2b]fluorene (5), which was four times alkylated, brominated with copper(II) bromide on an aluminum oxide matrix, and polymerized via a Ni(0)-mediated coupling reaction (Mn (3.3−3.9) × 104 (tuluene, polystyrene standards)). As expected, the wavelength data for absorption and emission are intermediate to those of PF and LPPP and prove the suitability of the polymer to be used as blue-light-emitting material in polymer light-emitting diodes. The polymer 8a,b is stable up to 380 °C and shows thermotropic liquid crystalline behavior at high temperatures (250−300 °C). Oligomers of the 6,6‘,12,12‘-tetraoctylindenofluorene (6a) have been synthesized by Ni(0)-induced coupling of monobromo and dibromo (7a) compounds, to determine the effective conjugation length (n∞,abs = 6−7, n∞,em = 5−6).
Article
A general synthesis of phosphonic diacid dichlorides (1) using oxalyl chloride and catalytic DMF is described.
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Poly [2,7-(9-oxo-9-phosphafluorenylene)-alt-co-(1,4-aryl-ene)]s, readily prepared from 2,7-dibromo-9-oxo-9-phosphafluorenes and arylene bisboronates, behaved as extended pi-conjugated polymers in the UV-vis absorption spectroscopy and displayed green-blue fluorescence with high quantum yields. Cyclic voltammetry revealed the polymers exhibited electrochromic behaviors and afforded a bandgap of ca. 2.8 eV, consistent with the value from the absorption edge.
Article
Thanks to their unique optical and electrochemical properties, conjugated polymers have attracted considerable attention over the last two decades and resulted in numerous technological innovations. In particular, their implementation in sensing schemes and devices was widely investigated and produced a multitude of sensory systems and transduction mechanisms. Conjugated polymers possess numerous attractive features that make them particularly suitable for a broad variety of sensing tasks. They display sensory signal amplification (compared to their small-molecule counterparts) and their structures can easily be tailored to adjust solubility, absorption/emission wavelengths, energy offsets for excited state electron transfer, and/or for use in solution or in the solid state. This versatility has made conjugated polymers a fluorescence sensory platform of choice in the recent years. In this review, we highlight a variety of conjugated polymer-based sensory mechanisms together with selected examples from the recent literature.
Article
We designed and synthesized air- and moisture-stable gallafluorenes in which two benzene rings were bridged by the four-coordinate gallium atoms. The series of gallafluorenes were prepared by introducing electron-donating and -withdrawing groups through Suzuki-Miyaura coupling reactions. The gallafluorenes showed unique emissions via their triplet states in the presence of B(C6F5)3. These emissions were obtained via the triplet exciplex of gallafluorene and B(C6F5)3.
Article
Three alternating donor–acceptor copolymers have been synthesized by Stille coupling polymerization of 2,6-(trimethyltin)−4,8-bis(5-dodecylthiophene-2-yl)benzo[1,2-b:4,5-b′]dithiophene with 1,3-dibromo-5-hexylthieno[3,4-c]pyrrole-4,6-dione, 4,7-dibromo-1,3-benzothiadiazole, and 5,7-dibromo-2,3-didodecylthieno[3,4-b]pyrazine, respectively. The synthesized polymers were tested in bulk heterojunction solar cells as blends with the acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The thienopyrroledione copolymer displayed a power conversion efficiency of 3.00% which was increased to 3.86% by application of the additive 1,8-diiodooctane (DIO). Tapping mode atomic force microscopy analysis indicated that there was an increase in the phase separation between polymer and PCBM, leading to an improvement in the performance upon the addition of DIO.