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Fluorescent conjugated polymers formulated in nanoparticles show attractive properties to be used as bioimaging probes. However, their fluorescence brightness is generally limited by quenching phenomena due to interchain aggregation in the confined nanoparticle space. In this work, branched conjugated polymer networks are investigated as a way to enhance the photoluminescence quantum yield of the resulting conjugated polymer nanoparticles (CPNs). 1,3,5-Tribromobenzene and 2,2',7,7'-tetrabromo-9,9'-spirobifluorene are chosen as branching moieties and are added in 3 or 5 mol % to the poly(p-phenylene ethynylene) (PPE) conjugated polymer synthesis. Nanoparticles of all samples are prepared via the combined miniemulsion/solvent evaporation technique. The optical properties of the branched polymers in solution and in nanoparticle form are then compared to those of the linear PPE counterpart. The fluorescence quantum yield of the CPNs increases from 5 to 11% for the samples containing 1,3,5-tribromobenzene. Furthermore, when 5 mol % of either branching molecule is used, the one-photon fluorescence brightness doubles. The nanoparticles show low cytotoxicity in A549 human lung carcinoma cells up to a concentration of 100 μg/mL for 24 h. They also exhibit good particle uptake into cells and compatibility with two-photon imaging. ispartof: ACS BIOMATERIALS SCIENCE & ENGINEERING vol:5 issue:4 pages:1967-1977 ispartof: location:United States status: published

Fluorescent conjugated polymers formulated in nanoparticles show attractive properties to be used as bioimaging probes. However, their fluorescence brightness is generally limited by quenching phenomena due to interchain aggregation in the confined nanoparticle space. In this work, branched conjugated polymer networks are investigated as a way to enhance the photoluminescence quantum yield of the resulting conjugated polymer nanoparticles (CPNs). 1,3,5-Tribromobenzene and 2,2',7,7'-tetrabromo-9,9'-spirobifluorene are chosen as branching moieties and are added in 3 or 5 mol % to the poly(

The incorporation of conjugated polyelectrolytes as cathode interlayers in organic photovoltaics has been proven to be an effective way to boost the device efficiency. Nevertheless, more detailed investigations of the structure property relationships of these interlayer materials, in particular related to the film deposition behavior, can provide further insights into their mode of action. With this aim, a series of ionic (co)polythiophenes is successfully synthesized via Kumada catalyst-transfer condensation polymerization and subsequent introduction of ionic moieties on the polymer side chains. Both the topology (i.e. homopolymers, random and block copolymers) and the amount of ionic groups are systematically varied. The polymers are fully characterized and then applied as cathode interlayers in polymer solar cells based on PCDTBT:PC71BM, affording an average efficiency increase of similar to 15%. The structural screening on one hand indicates that the efficiency gain is a rather general phenomenon for this material class. On the other hand, the best photovoltaic responses are observed for the conjugated polyelectrolytes with a higher triethylene glycol side chain ratio and the block copolymer structure performs slightly better as compared to the random copolymer with the same (50/50) monomer ratio. Based on these findings, the field can move on to a more rational development of novel interfacial materials and thereby push the device efficiency even further. This work was supported by the Research Foundation-Flanders (FWO) (project G.0415.14N and postdoctoral fellowship J.K.). S.G. acknowledges Hasselt University for her (BOF) doctoral grant. TA Instruments is acknowledged for the RHC equipment.

Boron dipyrromethene (BODIPY) dyes represent a particular class within the broad array of potential photosensitizers. Their highly fluorescent nature opens the door for theragnostic applications, combining imaging and therapy using a single, easily synthesized chromophore. However, near-infrared absorption is strongly desired for photodynamic therapy to enhance tissue penetration. Furthermore, singlet oxygen should preferentially be generated without the incorporation of heavy atoms, as these often require additional synthetic efforts and/or afford dark cytotoxicity. Solutions for both problems are known, but have never been successfully combined in one simple BODIPY material. Here, we present a series of compact BODIPY-acridine dyads, active in the phototherapeutic window and showing balanced brightness and phototoxic power. Although the donor-acceptor design was envisioned to introduce a charge transfer state to assist in intersystem crossing, quantum-chemical calculations refute this. Further photophysical investigations suggest the presence of exciplex states and their involvement in singlet oxygen formation. The authors thank Hasselt University and the University of Namur for continuing financial support (PhD scholarships J.D. and T.C.). M.K., B.C., and W.M. thank the Research Foundation-Flanders (FWO) for support through project G087718N, Hercules project GOH3816NAUHL, and the Scientific Research Community (WOG) "Supramolecular Chemistry and Materials" (W000620N). The calculations were performed on the computers of the "Consortium des equipements de Calcul Intensif" (CECI) (http://www.ceci-hpc.be), including those of the "UNamur Technological Platform of High-Performance Computing" (PTCI) (http://www.ptci.unamur.be), for which we gratefully acknowledge the financial support from the FNRS-FRFC, the Walloon Region, and the University of Namur (Conventions No. 2.5020.11, GEQ U.G006.15, U.G018.19, 1610468, and RW/GEQ2016). Maes, W (corresponding author), UHasselt Hasselt Univ, Inst Mat Res IMO, Design & Synth Organ Semicond DSOS, B-3590 Diepenbeek, Belgium ; IMEC, Associated Lab IMOMEC, Wetenschapspk 1, B-3590 Diepenbeek, Belgium. wouter.maes@uhasselt.be

Silver nanowire networks have demonstrated significant potential as semi-transparent electrodes for various applications. However, for their widespread utilisation in devices, upscaled coating technologies such as screen-printing need to be explored and related to this, the formulation of suitable inks is indispensable. This work contributes to this effort by the synthesis of Ag-NW based formulations. The rheological characteristics that are essential for screen-printing are obtained by the addition of hydrophobically modified cellulose. The electrical and optical characteristics of screen-printed features on PET are compared by a Van der Pauw method and UV–vis spectroscopy. Despite the presence of the cellulose additive, the screen-printed electrodes exhibit a transmittance from 92.8% to 57.3% and a sheet resistance down to 27 Ohm sq−1. Based on the percolation theory in composites, a mathematical expression is presented, which allows the in-depth analysis of the resulting opto-electrical properties. The application potential of the nanowire-containing formulations is finally demonstrated by screen-printing functional, flexible electroluminescent devices. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 641864.

Three extended molecular chromophores, differing in their central acceptor moiety and specifically designed as electron donor components for small molecule organic solar cells, are synthesized via a two-fold-C-H arylation protocol. Upon removal of the side products inherent to the applied direct (hetero) arylation procedure, a record power conversion efficiency of 5.1% is achieved. We acknowledge financial support from the Science Policy Office of the Belgian Federal Government (BELSPO; IAP 7/05 project FS2), the Agency for Innovation by Science and Technology in Flanders (IWT; PhD grants J. Brebels and T. Vangerven) and the Research Programme of the Research Foundation - Flanders (FWO; M.ERA-NET project RADESOL and projects G.0415.14N/G.0B67.15N).

Improvement of the power conversion efficiency and long term stability remains to be of crucial importance for the further development of polymer solar cells (PSCs). Herein, a donor–acceptor copolymer based on 4,8-di(thiophene-2′-yl)benzo[1,2-b:4,5-b′]dithiophene (DTBDT) and 4,7-di(thiophene-2′-yl)benzo[c][1,2,5]thiadiazole (DTBT), specifically selected because of its suitability for roll-coating in the ambient environment, is investigated in terms of operational stability via partial exchange (5 or 10%) of the alkyl side chain on either the donor or the acceptor monomer with a 2-hydroxyethyl or 2-phenylethyl group. It is shown that the exchange of the hexyl chain on the DTBT moiety has a negative impact on the stability of the polymer as well as on the performance of the resulting PSCs. On the other hand, partial exchange of the 2-hexyldecyl side chain of the BDT unit by a 2-hydroxyethyl group results in an improved photochemical stability of the polymer film and a higher efficiency of 5.6% for the spin-coated PSC. The stability of roll-coated devices also slightly increases with the incorporation of 10% of either the 2-hydroxyethyl or 2-phenylethyl side chain.

To explore the effectiveness of monofluorinated isoindigo as an electron-deficient building block in push-pull conjugated polymers for organic solar cell applications, four low bandgap copolymers are effectively synthesized and characterized. The effects of fluorine introduction, thiophene spacer length and polymer molar mass on the general electro-optical polymer characteristics, thin film blend microstructure and electronic performance are investigated. Isoindigo monofluorination effectively improves the power conversion efficiency from 2.8 up to 5.0% upon molar mass optimization, without using any processing additives or post-treatments.

Organic photovoltaics (OPVs) have acquired huge attention over the past years as potential renewable energy sources, adding attractive features such as aesthetics, semi-transparency, flexibility, large area printability, improved low-light performance, and cost-effectiveness to the well-known Si-based photovoltaics. Steady improvements in OPV power conversion efficiencies are continuously reported, notably for bulk heterojunction solar cells based on conjugated polymer:fullerene blends. However, apart from efficiency and cost, the stability of organic solar cell devices is of particular concern. Among the different factors contributing to OPV instability, gradual loss of the optimum phase-separated nanomorphology of the photoactive layer blend is a critical parameter. In this paper, we present the results of ‘shelf-life’ accelerated lifetime tests performed for devices containing a range of functionalized poly(3-alkylthiophene) (P3AT) donor polymers upon prolonged thermal stress. By the incorporation of functional moieties on the side chains of P3HT-based copolymers, a remarkable improvement of the intrinsic stability of the active layer blend morphology is accomplished, even for fairly low built-in ratios (5–15%) and without crosslinking to covalently anchor the polymer and/or fullerene molecules. Moreover, these alterations do not influence the initial power conversion efficiencies to a large extent. As such, the presented approach can be regarded as an attractive paradigm for OPV active layer stability.

A series of thiazolo[5,4-d]thiazole-based small molecule organic optoelectronic materials is synthesized via a straightforward microwave-activated Pd-catalyzed C-H arylation protocol. The procedure allows us to obtain extended 2,5-dithienylthiazolo[5,4-d]thiazole chromophores with tailor-made energy levels and absorption patterns, depending on the introduced (het)aryl moieties and the molecular (a)symmetry, by shortened sequences without organometallic intermediates. The synthesized materials can be applied as either electron donor or electron acceptor light-harvesting materials in molecular bulk heterojunction organic solar cells.

The degradation pattern of a series of low band gap PCPDTBT polymers under thermal stress is investigated by in situ UV-vis and FT-IR techniques combined with thermal degradation analysis. Thermogravimetric analysis is used to predetermine the decomposition intervals, revealing that thermolysis occurs in two stages. TG-TD-GC/MS shows that loss of the alkyl side chains pre- dominantly happens within the first temperature regime and deg- radation of the polymer backbone occurs thereafter. UV-vis spectroscopy is used to monitor the evolution of the optical proper- ties upon heating, reflecting the thermal stability of the conjugated backbone, whereas FT-IR spectroscopy is applied to evaluate the chemical changes under thermal stress, with an emphasis on the polymer periphery. The influence of the side chains and possible defects, dependent on the synthesis protocol applied, on the ther- mal stability of the final polymers is discussed and is related to the application of said materials in organic photovoltaics. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4912-4922

In the field of polymer solar cells, improving photovoltaic performance has been the main driver over the past decade. To achieve high power conversion efficiencies, a plethora of new photoactive donor polymers and fullerene derivatives have been developed and blended together in bulk heterojunction active layers. Simultaneously, further optimization of the device architecture is also of major importance. In this respect, we report on the use of specific types of electron transport layers to boost the inherent I-V properties of polymer solar cell devices, resulting in a considerable gain in overall photovoltaic output. Imidazolium-substituted polythiophenes are introduced as appealing electron transport materials, outperforming the currently available analogous conjugated polyelectrolytes, mainly by an increase in short-circuit current. The molecular weight of the ionic polythiophenes has been identified as a crucial parameter influencing performance.

The mass production technique of gravure contact printing is used to fabricate state-of-the art polymer field-effect transistors (FETs). Using plastic substrates with prepatterned indium tin oxide source and drain contacts as required for display applications, four different layers are sequentially gravure-printed: the semiconductor poly(3-hexylthiophene-2,5-diyl) (P3HT), two insulator layers, and an Ag gate. A crosslinkable insulator and an Ag ink are developed which are both printable and highly robust. Printing in ambient and using this bottom-contact/top-gate geometry, an on/off ratio of 10 4 and a mobility of 0.04cm 2 V -1 s -1 are achieved. This rivals the best top-gate polymer FETs fabricated with these materials. Printing using low concentration, low viscosity ink formulations, and different P3HT molecular weights is demonstrated. The printing speed of 40 m min -1 on a flexible polymer substrate demonstrates that very high-volume, reel-to-reel production of organic electronic devices is possible.

The stability of polymer solar cells (PSCs) can be influenced by the introduction of particular moieties on the conjugated polymer side chains. In this study, two series of donor-acceptor copolymers, based on bis(thienyl)dialkoxybenzene donor and benzo[c][1,2,5]thiadiazole (BT) or thiazolo[5,4-d]thiazole (TzTz) acceptor units, were selected toward effective device scalability by roll-coating. The influence of the partial exchange (5% or 10%) of the solubilizing 2-hexyldecyloxy by alternative 2-phenylethoxy groups on efficiency and stability was investigated. With an increasing 2-phenylethoxy ratio, a decrease in solar cell efficiency was observed for the BT-based series, whereas the efficiencies for the devices based on the TzTz polymers remained approximately the same. The photochemical degradation rate for PSCs based on the TzTz polymers decreased with an increasing 2-phenylethoxy ratio. Lifetime studies under constant sun irradiance showed a diminishing initial degradation rate for the BT-based devices upon including the alternative side chains, whereas the (more stable) TzTz-based devices degraded at a faster rate from the start of the experiment upon partly exchanging the side chains. No clear trends in the degradation behavior, linked to the copolymer structural changes, could be established at this point, evidencing the complex interplay of events determining PSCs' lifetime. This work has been supported by the Villum Foundation's Young Investigator Program (second round; project: Materials for Energy Production). The work was partly done during an external research stay of Ilona Heckler at Hasselt University in the group of Wouter Maes. The Hasselt University co-authors acknowledge the support by the IAP (Interuniversity Attraction Poles) 7/05 project FS2 (Functional Supramolecular Systems), granted by the Science Policy Office of the Belgian Federal Government (BELSPO), and the Research Foundation-Flanders (Fonds voor Wetenschappelijk Onderzoek-Vlaanderen) (Projects G.0415.14N, G.0B67.15N and M.ERA-NET Project RADESOL).

Although controlled polymerization procedures for conjugated polymers have considerable advantages with respect to molar mass and end group control, the material scope has been very limited, in particular considering block copolymers and donor–acceptor type all-conjugated polymers, imposing considerable challenges upon the synthetic polymer community. In this work, a push–pull monomer consisting of a thiophene (donor) and a pyridine (acceptor) unit is synthesized and subsequently polymerized via Kumada catalyst-transfer polymerization using a nickel catalyst (GRIM polymerization). In this way, an alternating donor–acceptor copolymer is obtained via a chain-growth mechanism. Furthermore, an all-conjugated block copolymer containing a poly(3-hexylthiophene) block and the alternating copolymer is successfully prepared in a one-pot procedure as well. The diblock structure is confirmed by comparison of the thermal, electrochemical, and spectroscopic properties of the block copolymer and its constituting polymer parts. This work was supported by the IAP 7/05 project “Functional Supramolecular Systems”, granted by the Science Policy Office of the Belgian Federal Government (BELSPO). We are also grateful for financial support by the Research Program of the Research Foundation−Flanders (FWO) (project G.0415.14N). S.G. acknowledges Hasselt University for her (BOF) doctoral grant. TA Instruments is acknowledged for the RHC equipment.

We have studied the elimination reaction of n-alkylsulfinyl−PPV and −OC1C10−PPV precursor polymers toward conjugated materials with in situ FT-IR and UV−vis spectroscopy. The temperature at which t...

Blue light-emitting poly(p-phenylene vinylene) (PPV) derivatives were prepared by use of the precursor “sulphinyl route” developed within our group a few years ago. These polymers have a maximum PL absorption at 447 or 468 nm depending on the film preparation. These polymers were tested in light-emitting diodes. The results are discussed.

A series of fully conjugated quinoxaline-based oligophenylene macrocycles is synthesized by Ni(0)-mediated Yamamoto-type diaryl homocoupling of (fluorinated) 2,3-bis(4'-bromophenyl)quinoxaline precursors. Cyclotrimers and cyclotetramers are obtained as the dominant reaction products. The cyclooligomers are fully characterized, including single-crystal X-ray structures, and their optoelectronic properties are analyzed with respect to possible applications in host-guest chemistry and organic electronics.