| 1. |
- Crivillers, N, et al.
(author)
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Photoinduced work function changes by isomerization of a densely packed azobenzene-based SAM on Au: a joint experimental and theoretical study
- 2011
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 13:32, s. 14302-14310
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Journal article (peer-reviewed)abstract
- Responsive monolayers are key building blocks for future applications in organic and molecular electronics in particular because they hold potential for tuning the physico-chemical properties of interfaces, including their energetics. Here we study a photochromic SAM based on a conjugated azobenzene derivative and its influence on the gold work function (Phi(Au)) when chemisorbed on its surface. In particular we show that the Phi(Au) can be modulated with external stimuli by controlling the azobenzene trans/cis isomerization process. This phenomenon is characterized experimentally by four different techniques, kelvin probe, kelvin probe force microscopy, electroabsorption spectroscopy and ultraviolet photoelectron spectroscopy. The use of different techniques implies exposing the SAM to different measurement conditions and different preparation methods, which, remarkably, do not alter the observed work function change (Phi(trans)-Phi(cis)). Theoretical calculations provided a complementary insight crucial to attain a deeper knowledge on the origin of the work function photo-modulation.
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| 2. |
- Fenwick, O., et al.
(author)
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Efficient red electroluminescence from diketopyrrolopyrrole copolymerised with a polyfluorene
- 2013
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In: APL Materials. - : AIP Publishing. - 2166-532X. ; 1:3, s. Art. no. 032108-
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Journal article (peer-reviewed)abstract
- We report the synthesis, characterization, and device incorporation of copolymers based on a common green-emitting polyfluorene but containing a small proportion of a low energy gap donor-acceptor-donor unit for red emission in photo- and electroluminescence. At just 1%-3% random incorporation, the low-gap unit is not present on all chains, yet we demonstrate that efficient charge and energy transfer can yield electroluminescent devices with 1% quantum efficiency and a color that can be tuned by adjusting the density of low-gap units to achieve primary red (National Television System Committee). The high current density tail off in the efficiency is reduced by replacing the hole-injection layer with a photochemically cross-linked electron-blocking layer.
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| 3. |
- Sforazzini, G., et al.
(author)
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Synthesis and Photophysics of Coaxial Threaded Molecular Wires: Polyrotaxanes with Triarylamine Jackets
- 2014
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:8, s. 4553-4566
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Journal article (peer-reviewed)abstract
- Conjugated polyrotaxanes jacketed with hole-transport groups have been synthesized from water-soluble polyrotaxanes consisting of a polyfluorene-alt-biphenylene (PFBP) conjugated polymer threaded through beta-cyclodextrin macrocycles. The hydroxyl groups of the oligosaccharides were efficiently functionalized with triphenylamine (TPA) so that every polyrotaxane molecule carries a coat of about 200 TPA units, forming a supramolecular coaxial structure. This architecture was characterized using a range of techniques, including small-angle X-ray scattering. Absorption of light by the TPA units results in excitation energy transfer (EET) and photoinduced electron transfer (ET) to the inner conjugated polymer core. These energy- and charge-transfer processes were explored by steady-state and time-resolved fluorescence spectroscopy, femtosecond transient absorption spectroscopy, and molecular modeling. The time-resolved measurements yielded insights into the heterogeneity of the TPA coat: those TPA units which are close to the central polymer core tend to undergo ET, whereas those on the outer surface of the polyrotaxane, far from the core, undergo EET. Sections of the backbone that are excited indirectly via EET tend to be more remote from the TPA units and thus are less susceptible to electron-transfer quenching. The rate of EET from the TPA units to the PFBP core was effectively modeled by taking account of the heterogeneity in the TPA-PFBP distance, using a distributed monopole approach. This work represents a new strategy for building and studying well-defined arrays of >100 covalently linked chromophores.
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| 4. |
- Steckler, Timothy, 1979, et al.
(author)
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Multifunctional materials for OFETs, LEFETs and NIR PLEDs
- 2014
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In: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 2:26, s. 5133-5141
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Journal article (peer-reviewed)abstract
- A family of phthalimide-thiophene copolymers with linear and branched alkyl chains attached to the imide nitrogen have been synthesized. Their optical and electronic properties were investigated along with their applications in OFETs and LEFETs. The phthalimide-thiophene copolymer having a C16 straight alkyl chain on the phthalimide yielded the highest mobilities and PLQE with mobilities of 1 x 10(-3) cm(2) V-1 s(-1) for holes and 1 x 10(-2) cm(2) V-1 s(-1) for electrons with a PLQE of similar to 28% in the solid state. Since these polymers are ambipolar and emissive, they have proven to be useful for applications as a host material for NIR PLEDs. In this study a 1% loading of NIR emitting DAD segments based on bisthienyl(thiadiazoloquinoxaline) or bisthienyl(benzotriazolothiadiazole) were incorporated into the phthalimide-thiophene polymerization. Using the branched CH(C8H17)(2) alkyl chain on the host phthalimide-thiophene copolymer combined with the bisthienyl(benzotriazolothiadiazole) emitter resulted in the most efficient (emission maximum >= 850 nm) single layer NIR-emitting PLED to date with an EQE of 0.27% emitting at 885 nm.
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| 5. |
- Steckler, Timothy, 1979, et al.
(author)
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Near-Infrared Polymer Light-Emitting Diodes Based on Low-Energy Gap Oligomers Copolymerized into a High-Gap Polymer Host
- 2013
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In: Macromolecular Rapid Communications. - : Wiley. - 1022-1336 .- 1521-3927. ; 34:12, s. 990-996
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Journal article (peer-reviewed)abstract
- Near-infrared (NIR) polymer light-emitting diodes (PLEDs) based on a fluorene-dioctyloxyphenylene wide-gap host material copolymerized with a low-gap emitter are presented. Various loadings (1, 2.5, 10, 20 mol%) of the low-gap emitter are studied, with higher loadings leading to decreased efficiencies likely due to aggregation effects. While the 10 mol% loading resulted in almost pure NIR emission (>99.6%), the 1 mol% loading yielded optimum device performance, which is among the best reported to date for a unblended single-layer pure polymer emitter, with an external quantum efficiencies of 0.04% emitting at 909 nm. The high spectral purity of the PLEDs combined with their performance support the methodology of copolymerization as an effective strategy for developing NIR PLEDs.
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