Showing papers by "Stephen Barlow published in 2012"
TL;DR: It is shown that surface modifiers based on polymers containing simple aliphatic amine groups substantially reduce the work function of conductors including metals, transparent conductive metal oxides, conducting polymers, and graphene.
Abstract: Organic and printed electronics technologies require conductors with a work function that is sufficiently low to facilitate the transport of electrons in and out of various optoelectronic devices. We show that surface modifiers based on polymers containing simple aliphatic amine groups substantially reduce the work function of conductors including metals, transparent conductive metal oxides, conducting polymers, and graphene. The reduction arises from physisorption of the neutral polymer, which turns the modified conductors into efficient electron-selective electrodes in organic optoelectronic devices. These polymer surface modifiers are processed in air from solution, providing an appealing alternative to chemically reactive low–work function metals. Their use can pave the way to simplified manufacturing of low-cost and large-area organic electronic technologies.
1,870 citations
TL;DR: Using ultralow doping, a study of the controlled passivation of acceptor tail states in fullerene C(60) by the addition of electrons introduced by molecular n doping is presented.
Abstract: Tail states in organic semiconductors have a significant influence on device performances by acting as traps in charge transport. We present a study of the controlled passivation of acceptor tail states in fullerene ${\mathrm{C}}_{60}$ by the addition of electrons introduced by molecular $n$ doping. Using ultralow doping, we are able to successively fill the traps with charges and examine the changes in conductivity, activation energy, mobility, and Fermi-level position. Passivation of the traps leads to an increase of the electron mobility in ${\mathrm{C}}_{60}$ by more than 3 orders of magnitude, to reach $0.21\text{ }\text{ }{\mathrm{cm}}^{2}/(\mathrm{V}\text{ }\mathrm{s})$.
236 citations
TL;DR: Air-stable dimers of sandwich compounds including rhodocene and (pentamethylcyclopentadienyl)(arene)ruthenium and iron derivatives can be used for n-doping electron-transport materials with electron affinities as small as 2.8 eV.
Abstract: Air-stable dimers of sandwich compounds including rhodocene and (pentamethylcyclopentadienyl)(arene)ruthenium and iron derivatives can be used for n-doping electron-transport materials with electron affinities as small as 2.8 eV. A p-i-n homojunction diode based on copper phthalocyanine and using rhodocene dimer as n-dopant shows a rectification ratio of greater than 10(6) at 4 V.
171 citations
TL;DR: The ability to extend the π system along the equatorial axis of rylenes not only leads to broadened light absorption but also increases the electron affinity, which can facilitate electron injection and transport with ambient stability.
Abstract: Hybrid rylene arrays have been prepared via a combination of Stille coupling and C–H transformation. The ability to extend the π system along the equatorial axis of rylenes not only leads to broadened light absorption but also increases the electron affinity, which can facilitate electron injection and transport with ambient stability.
124 citations
TL;DR: In this paper, a solution-based n-doping of the polymer poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis (dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} [P(NDI2OD-T2)] and the small molecule 6,13-bis-(tri(isopropyl)silylethynyl)pentac
Abstract: Solution-based n-doping of the polymer poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} [P(NDI2OD-T2)] and the small molecule 6,13-bis(tri(isopropyl)silylethynyl)pentacene (TIPS-pentacene) is realized with the air-stable dimers of rhodocene, [RhCp2]2, and ruthenium(pentamethylcyclopentdienyl)(1,3,5-triethylbenzene), [Cp*Ru(TEB)]2. Fermi level shifts, measured by direct and inverse photoemission spectroscopy, and orders of magnitude increase in current density and film conductivity point to strong n-doping in both materials. The strong reducing power of these air-stable dopants is demonstrated through the n-doping of TIPS-pentacene, a material with low electron affinity (3.0 eV). Doping-induced reduction of the hopping transport activation energy indicates that the increase in film conductivity is due in part to the filling of deep gap states by carriers released by the dopants.
95 citations
TL;DR: A new solution-processable small-molecule containing electron-poor naphthalene diimide and tetrazine moieties has been synthesized and optimized spin-coated n-channel OFETs on glass substrate shows electron mobility value up to 0.15 cm(2) V(-1) s(-1).
Abstract: A new solution-processable small-molecule containing electron-poor naphthalene diimide and tetrazine moieties has been synthesized. The optimized spin-coated n-channel OFETs on glass substrate shows electron mobility value up to 0.15 cm(2) V(-1) s(-1) . Inkjet-printed OFETs are fabricated in ambient atmosphere on flexible plastic substrates, which exhibits an electron mobility value up to 0.17 cm(2) V(-1) s(-1) and also shows excellent environmental and operational stability.
72 citations
TL;DR: Computational and electron spin resonance (ESR) evidence for displacement of the diabatic states into the bridge (reduced R(ab)) suggests that these values are underestimates and that even more variation is to be expected through the series.
Abstract: Radical cations have been generated for 10 bis[4-(diarylamino)styryl]arenes and heteroarenes to investigate the effect of the electron-richness of the terminal groups and of the bridging (hetero)arene on delocalization. The intervalence charge-transfer bands of these radical cations vary from weak broad Gaussians, indicative of localized class-II mixed-valence species, to strong relatively narrow asymmetric bands, characteristic of delocalized class-III bis(diarylamino) species, to narrow symmetric bands in cases where the bridge contribution to the singly occupied molecular orbital is largest. Hush analysis of these bands yields estimates of the electronic coupling varying from 480 cm–1 (electron-poor bridge, most electron-rich terminal aryl groups) to 1000 cm–1 (electron-rich bridge, least electron-rich termini) if the diabatic electron-transfer distance, Rab, is equated to the N–N separation. Computational and electron spin resonance (ESR) evidence for displacement of the diabatic states into the bridg...
68 citations
TL;DR: Kinetic measurements suggest that the solution reduction of 3 by 1 b(2) can occur by both the mechanism established for the Group 8 species and by a mechanism in which an endergonic dissociation of the dimer is followed by rapid electron transfer from monomeric 1 b to 3.
Abstract: Several 19-electron sandwich compounds are known to exist as "2×18-electron" dimers. Recently it has been shown that, despite their air stability in the solid state, some of these dimers act as powerful reductants when co-deposited from either the gas phase or from solution and that this behavior can be useful in n-doping materials for organic electronics, including compounds with moderate electron affinities, such as 6,13-bis[tri(isopropyl)silylethynyl]pentacene (3). This paper addresses the mechanisms by which the dimers of 1,2,3,4,5-pentamethylrhodocene (1 b(2)), (pentamethylcyclopentadienyl)(1,3,5-trialkylbenzene)ruthenium (alkyl=Me, 2 a(2); alkyl=Et, 2 b(2)), and (pentamethylcyclopentadienyl)(benzene)iron (2 c(2)) react with 3 in solution. Vis/NIR and NMR spectroscopy, and X-ray crystallography indicate that the products of these solution reactions are 3(·-) salts of the monomeric sandwich cations. Vis/NIR kinetic studies for the Group 8 dimers are consistent with a mechanism whereby an endergonic electron transfer from the dimer to 3 is followed by rapid cleavage of the dimer cation. NMR crossover experiments with partially deuterated derivatives suggest that the C-C bond in the 1 b(2) dimer is much more readily broken than that in 2 a(2); consistent with this observation, Vis/NIR kinetic measurements suggest that the solution reduction of 3 by 1 b(2) can occur by both the mechanism established for the Group 8 species and by a mechanism in which an endergonic dissociation of the dimer is followed by rapid electron transfer from monomeric 1 b to 3.
66 citations
TL;DR: In this paper, the authors investigated trap-state passivation by adding ultra-low amounts of n-dopants in organic field-effect transistors (OFET) made of as-received and purified fullerene C60.
Abstract: We investigate trap-state passivation by addition of ultra-low amounts of n-dopants in organic field-effect transistors (OFET) made of as-received and purified fullerene C60. We find a strong dependence of the OFET threshold voltage (VT) on the density of traps present in the layer. In the case of the unpurified material, VT is reduced from 17.9 V to 4.7 V upon trap passivation by a dopant:C60 ratio of ∼10−3, while the Ion/off current ratio remains high. This suggests that ultra-low doping can be used to effectively compensate impurity and defect-related traps.
62 citations
TL;DR: The utility of these precursors in palladium catalyzed cross-coupling reactions is demonstrated by the synthesis of bi- and ter-NDI derivatives, UV-vis, cyclic voltammetry, and n-channel organic field-effect transistor data for which are compared to those of the monomeric parent NDI.
53 citations
TL;DR: Dithiophenyldiketopyrrolopyrroles can be directly (hetero)arylated in moderate to excellent yields by Pd-catalyzed coupling to the CH position of a fluoro-hetero)-arene (in the presence of Ag2CO3) or the CBr position of bromo(hetero-arene).
Abstract: Dithiophenyldiketopyrrolopyrroles can be directly (hetero)arylated in moderate to excellent yields by Pd-catalyzed coupling to the CH position of a fluoro(hetero)arene (in the presence of Ag2CO3) or the CBr position of a bromo(hetero)arene.
TL;DR: In this article, two sulfonamide-functionalized dibenzophenazine-based sensors are reported to be effective fluorescent turn-on sensors for several anions, such as acetate, benzoate, cyanide, and fluoride.
TL;DR: A series of conjugated polymers has been synthesized by Sonogashira coupling of N,N′-bis(2-octyldodecyl)-2,6-dibromonaphthalene-1,4,5,8-bis (dicarboximide) and four para-diethynylbenzene derivatives.
TL;DR: In this paper, the authors report on high-mobility top-gate organic field effect transistors (OFETs) and complementary-like inverters fabricated with a solution-processed molecular bis(naphthalene diimide)-dithienopyrrole derivative as the channel semiconductor and a CYTOP/Al2O3 bilayer as the gate dielectric.
TL;DR: In this paper, Perylene-3,4,9,10-tetracarboxylic diimides (PDI) have been linked to norbornene through either an imide or a bay position.
TL;DR: Transient-absorption spectra of PDI-grafted polymers provide evidence for efficient electron transfer following either donor or acceptor photoexcitation to form long-lived charge-separated species, which exhibit strong absorption in the NIR.
Abstract: This paper reports the synthesis, photophysical behavior, and use in nanosecond optical-pulse suppression of a poly(2,7-carbazole-alt-2,7-fluorene) and a poly(3,6-carbazole-alt-2,7-fluorene) in which the carbazole N-positions are linked by an alkyl chain to one of the nitrogen atoms of a perylene-3,4,9,10-tetracarboxylic diimide (PDI) acceptor. It was found that the PDI pendants on the polymer side chain aggregated even in dilute solution, which extended the onset of PDI absorption into the near-infrared (NIR). Transient-absorption spectra of these polymers provide evidence for efficient electron transfer following either donor or acceptor photoexcitation to form long-lived charge-separated species, which exhibit strong absorption in the NIR. The spectral overlap between the transient species and the long-wavelength absorption edge of the aggregated PDI leads to reverse saturable absorption at 680 nm that can be used for optical-pulse suppression. Additionally, at high input energies, two-photon absorptio...
TL;DR: 2, 6-Diacyl derivatives of naphthalene-1,8:4,5-bis(dicarboximide)s have been synthesized via Stille coupling reactions of the corresponding 2,6-distannyl derivative with acyl halides.
Abstract: 2,6-Diacyl derivatives of naphthalene-1,8:4,5-bis(dicarboximide)s have been synthesized via Stille coupling reactions of the corresponding 2,6-distannyl derivative with acyl halides. Reaction of these diketones with hydrazine gave phthalazino[6,7,8,1-lmna]pyridazino[5,4,3-gh][3,8]phenanthroline-5,11(4H,10H)-dione fused-ring derivatives. The products were characterized by UV–vis absorption spectroscopy and electrochemistry, modeled using density functional theory calculations, and, in some cases, studied and compared using single-crystal X-ray diffraction.
TL;DR: Ozonolysis of the 2,6-divinyl derivative of a naphthalene diimide (NDI) affords a 2, 6-diformyl-NDI, which can be used in Knoevenagel condensation reactions, as demonstrated by the synthesis of a 2.6-bis(2,2-dicyanovinyl)-NDI.
Abstract: Ozonolysis of the 2,6-divinyl derivative of a naphthalene diimide (NDI) affords a 2,6-diformyl-NDI, which can be used in Knoevenagel condensation reactions, as demonstrated by the synthesis of a 2,6-bis(2,2-dicyanovinyl)-NDI. UV–vis absorption and electrochemical data are compared to those of the parent NDI.
TL;DR: In this article, the role of interfacial energetics and morphology in influencing the separation of CT states into dissociated charge carriers was examined in a series of perylene-3,4:9,10-tetracarboxydiimide (PDI) electron acceptors.
Abstract: We focus upon the role of interfacial energetics and morphology in influencing the separation of CT states into dissociated charge carriers. In particular, we undertake transient optical studies of films comprising regioregular poly(3-hexylthiophene) (P3HT) blended with a series of perylene-3,4:9,10-tetracarboxydiimide (PDI) fullerene electron acceptors. For the PDI film series, we observe a close correlation between the PDI electron affinity and the efficiency of charge separation. This correlation is discussed in the context of studies of charge photogeneration for other organic donor/acceptor blend films, including other polymers, blend compositions, and the widely used electron phenyl-C61-butyric acid methyl ester(PCBM). Furthermore, we compare the charge recombination dynamics observed in films comprising P3HT blended with three fullerene derivatives: PCBM and two alternative pyrazolinofullerenes. Transient absorption data indicate that replacement of PCBM with either of the pyrazolinofullerene derivatives results in a transition from nongeminate to monomolecular (geminate) recombination dynamics. We show that this transition cannot be explained by a difference in interfacial energetics. However, this transition does correlate with nanomorphology data that indicate that both pyrazolinofullerenes yield a much finer phase segregation with correspondingly smaller domain sizes than observed with PCBM. Our results therefore provide clear evidence of the role of nanomorphology in determining the nature of recombination dynamics in such donor/acceptor blends.
TL;DR: It is shown that the double pump-probe technique is optimized by working in the saturable absorption regime and the analytical model presented is applicable to both the reverse saturable and the saturables absorption regimes.
Abstract: The double pump–probe technique (DPP), first introduced by Swatton et al. [Appl. Phys. Lett.1997, 71, 10], is a variant of the standard pump–probe method but uses two pumps instead of one to create two sets of initial conditions for solving the rate equations, allowing a unique determination of singlet- and triplet-state absorption parameters and transition rates. We investigate the advantages and limitations of the DPP theoretically and experimentally and determine the influence of several experimental parameters on its accuracy. The accuracy with which the DPP determines the triplet-state parameters improves when the fraction of the population in the triplet state relative to the ground state is increased. To simplify the analysis of the DPP, an analytical model is presented, which is applicable to both the reverse saturable and the saturable absorption regimes. We show that the DPP is optimized by working in the saturable absorption regime. Although increased accuracy is in principle achievable by incr...
TL;DR: In this paper, the crystal structures of nonamethyliridocenium hexafluorophosphate and 1,2,3,4,5-pentamethylrhodoceniumhexafloorophosphates have been determined and compared to related structures.
06 May 2012
TL;DR: In this paper, a perturbative few-state model with knowledge of the linear and two-photon absorption spectra was used to predict the third-order nonlinear optical response.
Abstract: Dispersion of the third-order nonlinear optical response can be predicted using a perturbative few-state model approach with knowledge of the linear and two-photon absorption spectra. This approach has been applied toward polymethines and squaraines.