Temperature Dependence of Blue Phosphorescent Cyclometalated Ir(III) Complexes

The photophysical properties for a series of facial (fac) cyclometalated Ir(III) complexes (fac-Ir(C^N)_3 (C^N = 2-phenylpyridyl (ppy), 2-(4,6-difluorophenyl)pyridyl (F2ppy), 1-phenylpyrazolyl (ppz), 1-(2,4-difluorophenyl)pyrazolyl) (F2ppz), and 1-(2-(9,9′-dimethylfluorenyl))pyrazolyl (flz)), fac-Ir(C^N)_2(C^N′) (C^N = ppz or F2ppz and C^N′ = ppy or F2ppy), and fac-Ir(CC′)_3 (C^C′ = 1-phenyl-3-methylbenzimidazolyl (pmb)) have been studied in dilute 2-methyltetrahydrofuran (2-MeTHF) solution in a temperature range of 77−378 K. Photoluminescent quantum yields (Φ) for the 10 compounds at room temperature vary between near zero and unity, whereas all emit with high efficiency at low temperature (77 K). The quantum yield for fac-Ir(ppy)_3 (Φ = 0.97) is temperature-independent. For the other complexes, the temperature-dependent data indicates that the luminescent efficiency is primarily determined by thermal deactivation to a nonradiative state. Activation energies and rate constants for both radiative and nonradiative processes were obtained using a Boltzmann analysis of the temperature-dependent luminescent decay data. Activation energies to the nonradiative state are found to range between 1600 and 4800 cm^−1. The pre-exponential factors for deactivation are large for complexes with C^N ligands (1011−1013 s^−1) and significantly smaller for fac-Ir(pmb)_3 (109 s^−1). The kinetic parameters for decay and results from density functional theory (DFT) calculations of the triplet state are consistent with a nonradiative process involving Ir−N (Ir−C for fac-Ir(pmb)_3) bond rupture leading to a five-coordinate species that has triplet metal-centered (^3MC) character. Linear correlations are observed between the activation energy and the energy difference calculated for the emissive and ^3MC states. The energy level for the ^3MC state is estimated to lie between 21700 and 24000 cm^−1 for the fac-Ir(C^N)_3 complexes and at 28000 cm^−1 for fac-Ir(pmb)_3

Remote doping of a pentacene transistor: Control of charge transfer by molecular-level engineering

© 2010 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.3491429DOI: 10.1063/1.3491429We demonstrate that holes from a p-doped N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) layer transfer to an adjacent pentacene film. The spatial separation of carriers from dopants, or remote doping, is demonstrated with a combination of photoemission spectroscopy and current-voltage measurements for a p-doped α-NPD/pentacene heterojunction. Increased conductivity of the pentacene film is observed in both nongated temperature-dependent conductivity and gated thin-film transistor measurements

High-performance N-channel Thin-Film Field Effect Transistors Based on Self-Assembly Polymer in Nanowire Suspension

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The Role of p Bridges in High-Efficiency DSCs Based on Unsymmetrical Squaraines

A series of squaraine-based sensitizers with various p bridges and anchors were prepared and examined in dye-sensitized solar cells. The carboxylic anchor group was attached onto a squaraine dye through p bridges with and without an ethynyl spacer. DFT studies indicate that the LUMO is delocalized throughout the dyes, whilst the HOMO resides on the squaraine core. The dye that incorporates a 4,4-di-n-hexyl-cyclopentadithiophene group that is directly attached onto the p bridge, JD10, exhibits the highest power conversion efficiency in a DSC; this result is attributed, in part, to the deaggregative properties that are associated with the gem-di-n-hexyl substituents, which extend above and below the p-conjugated dye plane. Dye JD10 demonstrates a power-conversion efficiency of 7.3?% for liquid-electrolyte dye-sensitized solar cells and 7.9?% for cells that are co-sensitized by another metal-free dye, D35, which substantially exceed the performance of any previously tested squaraine sensitizer. A panchromatic incident-photon-to-current-conversion efficiency curve is realized for this dye with an excellent short-circuit current of 18.0 mA?cm-2. This current is higher than that seen for other squaraine dyes, partially owing to a high molar absorptivity of >5?000?M-1?cm-1 from 400 nm to the long-wavelength onset of 724 nm for dye JD10

Pronounced Side Chain Effects in Triple Bond-Conjugated Polymers Containing Naphthalene Diimides for n-Channel Organic Field-Effect Transistors

Three triple bond-conjugated naphthalene diimide (NDI) copolymers, poly{[N,N'-bis(2-R-1)-naphtha-lene-1,4,5,8-bis(dicarboxlinid e)-2,6- diyl] [(2,5-bis (2-R-2) 1,4-phenylene)bis(ethyn-2,1-diyl)1} (PNDIR1-R-2), were synthesized via Sonogashira coupling polymerization with varying alkyl side chains at the nitrogen atoms of the imide ring and 2,5-positions of the 1,4-diethynylbenzene moiety. Considering their identical polymer backbone structures, the side chains were found to have a strong influence on the surface morphology/nanostructure, thus playing a critical role in charge-transporting properties of the three NDI-based copolymers. Among the polymers, the one with an octyldodecyl (OD) chain at the nitrogen atoms of imide ring and a hexadecyloxy (HO) chain at the 2,5-positions of 1,4-diethynylbenzene, P(NDIOD-HO), exhibited the highest electron mobility of 0.016 cm(2)V(-1) s(-1) as compared to NDI-based copolymers with an ethylhexyl chain at the 2,5-positions of 1,4-diethynylbenzene. The enhanced charge mobility in the P(NDIOD-HO) layers is attributed to the well-aligned nano-fiber-like surface morphology and highly ordered packing structure with a dominant edge-on orientation, thus enabling efficient in-plane charge transport. Our results on the molecular structure-charge transport property relationship in these materials may provide an insight into novel design of n type conjugated polymers for applications in the organic electronics of the future.11Nsciescopu

High-Performance n-Channel Thin-Film Field-Effect Transistors Based on a Nanowire-Forming Polymer

A new electrontransport polymer, poly{[N,N'-dioctylperylene-3,4,9,10-bis(dicarboximide)-1,7(6)-diyl]-alt-[(2,5-bis(2-ethyl-hexyl)-1,4-phenylene)bis(ethyn-2,1-diyl]} (PDIC8-EB), is synthesized. In chloroform, the polymer undergoes self-assembly, forming a nanowire suspension. The nanowire's optical and electrochemical properties, morphological structure, and field-effect transistor (FET) characteristics are investigated. Thin films fabricated from a PDIC8-EB nanowire suspension are composed of ordered nanowires and ordered and amorphous non-nanowire phases, whereas films prepared from a homogeneous PDIC8-EB solution consist of only the ordered and amorphous non-nanowire phases. X-ray scattering experiments suggest that in both nanowires and ordered phases, the PDIC8 units are laterally stacked in an edge-on manner with respect to the film plane, with full interdigitation of the octyl chains, and with the polymer backbones preferentially oriented within the film plane. The ordering and orientations are significantly enhanced through thermal annealing at 200 degrees C under inert conditions. The polymer film with high degree of structural ordering and strong orientation yields a high electron mobility (0.10 +/- 0.05 cm(2) V-1 s(-1)), with a high on/off ratio (3.7 x 10(6)), a low threshold voltage (8 V), and negligible hysteresis (0.5 V). This study demonstrates that the polymer in the nanowire suspension provides a suitable material for fabricating the active layers of high-performance n-channel FET devices via a solution coating process.X113327sciescopu