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Self-assembled monolayers of E-stilbene-4-thiolate (SAM1), E-4'-(ethoxy)stilbene-4-thiolate (SAM2), and E-4'-(dimethylamino)stilbene-4-thiolate (SAM3) on Au(111) have been obtained from reaction of ethanol solutions of the corresponding S-acetyl derivatives with gold substrates. A combination of X-ray photoelectron spectroscopy, ellipsometry, and infrared reflection absorption spectroscopy indicates that the monolayers are dense (ca. 3.3 x 10(14) molecules/cm(2)) and that the long molecular axes of the thiolates are approximately perpendicular to the surface. Ultraviolet photoelectron spectroscopy shows that formation of these monolayers decreases the work function of pristine Au by 0.9-1.3 eV, in part due to a bond dipole of ca. 4.4 D/molecule formed upon adsorption and partly due to the molecular dipole moment arising from the 4'-pi-donor substituents. However, the extent of the work function variation between SAM1, 2, and 3 is smaller than anticipated from purely electrostatic considerations.

A 7 times 11 pixel blue OLED display was fabricated using a patterned indium-tin-oxide (ITO) substrate. The fabrication process for an M times N pixel organic light-emitting diode (OLED) video display including an electrical insulating layer and a physical pixel separator layer is presented. An efficient and thermally stable blue fluorescent organic material, 6,6'-bis((2-p -biphenyl)-4-phenylquinoline) (B2PPQ), was used in combination with an evaporated hole-transport small molecule with a high ionization potential.

The electron spin resonance spectra of the radical cations of 4,4'-bis[di(4-methoxyphenyl)amino]tolane, E-4,4'-bis[di(4-methoxyphenyl)amino]stilbene, and E,E-1,4-bis{4-[di(4-methoxyphenyl)amino]styryl}benzene in dichloromethane exhibit five lines over a wide temperature range due to equivalent coupling to two 14N nuclei, indicating either delocalization between both nitrogen atoms or rapid intramolecular electron transfer on the electron spin resonance time scale. In contrast, those of the radical cations of 1,4-bis{4-[di(4-methoxyphenyl)amino]phenylethynyl}benzene and E,E-1,4-bis{4-[di(4-n-butoxyphenyl)amino]styryl}-2,5-dicyanobenzene exhibit line shapes that vary strongly with temperature, displaying five lines at room temperature and only three lines at ca. 190 K, indicative of slow electron transfer on the electron spin resonance time scale at low temperatures. The rates of intramolecular electron transfer in the latter compounds were obtained by simulation of the electron spin resonance spectra and display an Arrhenius temperature dependence. The activation barriers obtained from Arrhenius plots are significantly less than anticipated from Hush analyses of the intervalence bands when the diabatic electron-transfer distance, R, is equated to the N[symbol: see text]N distance. Comparison of optical and electron spin resonance data suggests that R is in fact only ca. 40% of the N[symbol: see text]N distance, while the Arrhenius prefactor indicates that the electron transfer falls in the adiabatic regime.

A solution-processable polynorbornene with pendant fluorescent and electron-transport silole groups was synthesized using ruthenium-complex-initiated ring-opening metathesis polymerization. A weight-average molecular weight around 59,300 and a low polydispersity index of 1.4 were estimated for the polymer using gel permeation chromatography. The thermal, electronic, photo- and electroluminescence properties of the polymer were investigated and compared with those of a small-molecule reference compound. The polymer exhibits better thermal stability than the small molecule and exhibits a glass transition temperature of 91 °C, while retaining the optical and electronic properties of the corresponding small-molecule silole. The room temperature electron mobility was measured using the time-of-flight technique to be 3.5 × 10 −5 cm 2 /V/s at an applied electric field of 7.5 × 10 5 V/cm. Organic light-emitting diodes fabricated using the polymer as the electron transport and emissive layer have low efficiencies; introduction of an additional tris(8-hydroxyquinolinato)aluminum (Alq 3 ) electron-transport layer leads not only to increased efficiency, but also to increased contributions to the electroluminescence from the Alq 3 .

Photoemission spectroscopy is used to probe the electronic properties, reactivity and energy level alignment at interfaces of tris{2,5-bis(3,5-bis-trifluoromethyl-phenyl)-thieno}[3,4-b,h,n]-1,4,5,8,9,12-hexaazatriphenylene (THAP) deposited on both medium and high work function metallic substrates. Crystalline and non-crystalline metal substrates are used in order to investigate the effect of both the work function and molecular orientation on the physical properties of the THAP layer.

n-Doping of copper phthalocyanine (CuPc), which has an electron affinity (EA) of 3.52 eV, by decamethylcobaltocene (DMC) is demonstrated. DMC has a remarkably low solid-state ionization energy (IE) of 3.3 eV, as measured by ultra-violet photoemission spectroscopy (UPS). Further UPS measurements show a large 1.4 eV upward shift of the Fermi-level within the single particle gap of CuPc between the p- and n-doped films. n-Doping is also confirmed by current–voltage (I–V) measurements, which show a 106-fold increase in current density due to improved electron injection and enhanced conductivity of the bulk film. An organic p–i–n CuPc homojunction is also fabricated using F4-TCNQ and DMC as p- and n-dopants, respectively. Current–voltage characteristics demonstrate excellent rectification with a turn on voltage of approximately 1.3 eV, which is consistent with the built-in voltage measured by UPS and capacitance–voltage (C–V) measurements.

Scanning tunneling microscopy is used to study the structure of monolayers of tris{2,5-bis(3,5-bis-trifluoromethyl-phenyl)-thieno}[3,4-b,h,n]-1,4,5,8,9,12-hexaaza-triphenylene adsorbed on a clean Ag(110) single-crystal surface. The molecules adsorb flat on the surface, forming two-dimensional islands within which intermolecular interactions constrain the molecules to form rows of molecular pairs. The balance between intermolecular and molecule–substrate interactions leads to two specific orientations of these rows at +11° and −11° from the [001] direction of the Ag(110) surface. A comparison between observed and calculated local densities of states shows an antiparallel azimuthal orientation of the molecules within the closely associated pairs. The structure of the full monolayer shows that the intermolecular interaction overcomes the interaction with the substrate, resulting in a reorientation of the rows along various directions.

By using gas-phase ultraviolet photoelectron spectroscopy, vis/NIR spectroscopy, and electronic-structure calculations, we have investigated the electron-vibration and electronic interactions in a series of bisdimethylamino mixed-valence systems: N,N,N′,N′-tetramethyl-p-phenylenediamine, N,N,N′,N′-tetramethylbenzidine, and N,N,N′,N′-tetramethyltolane-4,4′-diamine. Experiment and theory concur to indicate that the electron-vibration coupling in these systems is dominated by interactions with symmetric modes. The results reveal that the strength of both electronic and electron-vibration couplings decreases as the molecular bridge lengthens. The parameters derived for the present compounds have been compared to those of diarylamino-based structural analogs. This comparison underlines that the replacement of the methyl terminal groups with p-anisyl groups has a significant effect on the electronic and electron-vibrational interactions.

The diketones 4,4′-di[3,4-bis(n-dodecyloxy)styryl]benzil and 4,4′-di[3,4-bis(n-dodecyloxy)phenylethynyl]benzil have been synthesized from 4,4′-dibromobenzil using Heck coupling with the appropriate styrene and Sonogashira coupling with the appropriate phenylalkyne, respectively. Treatment of the distyrylbenzil derivative with phosphorus pentasulfide followed by nickel(II) chloride gave the corresponding extended nickel bis(dithiolene) derivative which shows strong near-infrared two-photon absorption with a cross-section of over 440 GM (1 GM = 10−50 cm4 s photon−1 molecule−1) throughout the telecommunications range and a peak cross-section of 5300 GM at ca. 1.2 μm.

The one-photon and two-photon absorption properties of cross-shaped chromophores consisting of four donor-substituted styryl branches linked to an aromatic core (benzene or pyrazine) have been investigated and compared with those of linear analogues with only two branches (donor−π−donor distryrylarenes). The areas of the lowest energy two-photon absorption bands of the compounds with four branches were less than twice those of analogues with two branches. The spectral features observed in these chromophores suggest that electronic coupling between the branches is effective but does not lead to significant enhancement of the two-photon cross section when the branches extend in more than one dimension. In a chromophore with two donor-substituted and two acceptor-substituted branches the two-photon cross section is smaller than in the corresponding linear analogues. The main characteristics of both the one-photon and two-photon spectra of multibranched compounds of the type discussed here can be explained qu...

We have investigated computationally the two-photon absorption (2PA) properties of donor-acceptor dipolar chromophores, the conjugated backbones of which contain two five-membered heterocyclic groups which may be electron-rich (thiophene-2,5-diyl) and/or electron-deficient (thiazole-2,5-diyl). Quantum-chemical calculations (INDO/MRDCI/S-tensor and Sum-Over-States calculations based on DFT-optimized geometries) indicate that the two-photon cross-sections into the lowest two excited states S 1 and S 2 can be tuned by more than an order of magnitude by varying the nature, order, and, in the case of thiazole, orientation of the heterocycles. Going from one thiazole regioisomer to the other has the strongest impact on the 2PA spectra and can even invert the ratio between the 2PA cross-sections of S 1 and S 2 . An essential-state analysis reveals that different channels dominate 2PA into S 1 and S 2 . The sensitivity of 2PA into S 1 towards the orientation of the thiazole ring stems from a local modulation on the thiazole ring of the change in state dipole moment upon excitation to S 1 , Δμ 01 , whereas the dominant essential parameter through which the thiazole orientation affects 2PA into S 2 is the transition dipole moment between S 1 and S 2 , μ 12 .

A comparative study of hole-mobility in N,N′-diphenyl-N,N′-di(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) using three independent measurement techniques is presented. Time-of-flight (TOF), steady-state space charge-limited current (SCLC) experiments are carried-out in neat films of TPD, sandwiched between electrodes with different work functions. Organic field-effect transistors (OFET) are fabricated from TPD thin films and their electrical properties characterized. The comparative results show that all-electrical measurements that involve carrier injection from a metal electrode into the organic film yield effective mobility values that are one order of magnitude lower than those obtained from time-of-flight experiments in which carriers are created in the film optically. Similarly, SCLC and TOF experiments were used to measure electron-mobility in a discoid organic compound 2,3,8,9,14,15-hexakis-dodecylsulfanyl-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA-(SC12H25)6).

Five diamines with thiophene-based bridges-(E)-1,2-bis-{5-[bis(4- butoxyphenyl)amino]-2-thienyljethylene (1), 5,5′-bis[bis(4-methoxyphenyl) amino]-2,2′-bithiophene (2), 2,6-bis[bis(4-butoxyphenyl)amino]dithieno[3, 2-b:2′,3′-d]thiophene (3), N-(4-tert-butylphenyl)-2,6-bis[bis(4- methoxyphenyl)amino]dithieno[3,2-b:2′,3′-d]pyrrole (4a) and N-tert-butyl-2,6-bis[bis(4-methoxyphenyl)amino]dithieno[3,2-b:2′, 3′-d]pyrrole (4b)-have been synthesised. The syntheses make use of the palladium(0)-catalysed coupling of brominated thiophene species with diarylamines, in some cases accelerated by microwave irradiation. The molecules all undergo facile oxidation, 4b being the most readily oxidised at about -0.4 V versus ferrocenium/ferrocene, and solutions of the corresponding radical cations were generated by addition of tris(4-bromophenyl)aminium hexachloroantimonate to the neutral species. The near-IR spectra of the radical cations show absorptions characteristic of symmetrical delocalised species (that is, class III mixed-valence species); analysis of these absorptions in the framework of Hush theory indicates strong coupling between the two amine redox centres, stronger than that observed in species with phenylenebased bridging groups of comparable length. The strong coupling can be attributed to high-lying orbitais of the thiophene-based bridging units. ESR spectroscopy indicates that the coupling constant to the amino nitrogen atoms is somewhat reduced relative to that in a stilbene-bridged analogue. The neutral species and the corresponding radical cations have been studied with the aid of density functional theory and time-dependent density functional theory. The DFT-calculated ESR parameters are in good agreement with experiment, while calculated spin densities suggest increased bridge character to the oxidation in these species relative to that in comparable species with phenylene-based bridges. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

Solution-processable copolymers with pendant phosphorescent iridium complexes and 2,7-di(carbazol-9-yl)fluorene-type host moieties were synthesized using ruthenium-catalyzed ring-opening metathesis polymerization. Low polydispersity indices and molecular weights around 20 000 Da were obtained for all copolymers. As a result of the living character of the polymerization of the monomer containing the host moiety, a high degree of control over the molecular weights of all copolymers can be obtained. The photo- and electroluminescence properties of the copolymers were investigated. All copolymers retained the photo- and electrophysical properties of the corresponding nonpolymeric iridium complexes. Furthermore, as a proof of principle for the potential use of these materials, organic light-emitting devices were fabricated using the orange-emitting copolymer. A maximum external quantum efficiency of 1.9% at 100 cd/m2 and a turn-on voltage of 3.7 V were obtained with photoluminescence quantum yield of 0.10 demo...

A norbornene-functionalized derivative of acetylacetone has been used to synthesize a series of new polymerizable norbornene-derivatized phosphorescent platinum complexes of the form Pt(C∧N)(O∧O*) where C∧N represents a cyclometalated ligand and O∧O* represents the functionalized acetylacetonate ligand. The complexes have been fully characterized, and the structures of three examples have been determined by X-ray diffraction. Solution absorption and luminescence spectra and electrochemical data are very similar to those for analogues without these polymerizable groups. A 9,9-dialkyl-2,7-di(carbazol-9-yl)fluorene material, in which one of the alkyl groups bears a norbornene group, has been synthesized and copolymerized with the Pt(C∧N)(O∧O*) complexes using Grubbs ruthenium catalysts, resulting in copolymers with broad molecular weight distributions. The copolymers have been used as lumophores in organic light-emitting diodes, thus demonstrating that platinum phosphors can be successfully integrated into t...

Scanning tunneling microscopy was used to study the morphological behavior of 1−2 monolayers (ML) of 5,6,11,12,17,18-hexaazatrinaphthylene (HATNA) deposited on Au(111). The first ML consisted of molecules flat on the surface, arranged in one of three different ordered phases depending on annealing parameters. The second ML assumed an upright orientation and tended to order only if the first layer was disordered. Scanning tunneling spectroscopy of 1−2 ML ordered HATNA was compared to ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy of 80 A amorphous HATNA. There is good agreement between techniques in the transport band gap (∼3.80 eV), but the position of the Fermi level in the gap is shifted in the tunneling spectra by about 0.75 eV toward the highest occupied molecular orbital. The shift may be due to morphological effects or degradation from ultraviolet light irradiation.

Several hexaazatrinaphthylene derivatives and a tris(thieno)hexaazatriphenylene derivative have been synthesised by reaction of the appropriate diamines with hexaketocyclohexane. The crystal structure of 2,3,8,9,14,15-hexachloro-5,6,11,12,17,18-hexaazatrinaphthylene has been determined by X-ray diffraction; this reveals a molecular structure in good agreement with that predicted by density functional theory (DFT) calculations and pi-stacking with an average spacing between adjacent molecular planes of 3.18 A. Solid-state ionisation potentials have been measured by using UV photoelectron spectroscopy and fall in the range of 5.99 to 7.76 eV, whereas solid-state electron affinities, measured using inverse photoelectron spectroscopy, vary in the range -2.65 to -4.59 eV. The most easily reduced example is a tris(thieno)hexaazatriphenylene substituted with bis(trifluoromethyl)phenyl groups; DFT calculations suggest that the highly exothermic electron affinity is due both to the replacement of the outermost phenylene rings of hexaazatrinaphthylene with thieno groups and to the presence of electron-withdrawing bis(trifluoromethyl)phenyl groups. The rather exothermic electron affinities, the potential for adopting pi-stacked structures and the low intramolecular reorganisation energies obtained by DFT calculations suggest that some of these molecules may be useful electron-transport materials.

The 2-dicyanomethylidene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) group has been identified as a particularly strong acceptor suitable for the realization of highly efficient second-order NLO chromophores. To provide guidelines for a further improvement of heterocyclic acceptors, we present Sum-Over-States (SOS) calculations of second-order polarizabilities (β) for a series of donor–π-bridge–acceptor (D–π–A) chromophores. In particular, we investigate the effect of replacing the oxygen atom of the furan ring in TCF by a variety of other groups, X (SiH2, CH2, CCH2, NH, CO, S, CCHNO2, SO, and SO2). Overall β is found to increase with the inductive electron-withdrawing character of X, with β being further increased or decreased when X has π-accepting or π-donating character. Within the framework of the two-level model, the effects associated with the π-donating and accepting character can be understood in terms of destabilizing and stabilizing effects on the lowest unoccupied molecular orbitals of the dipolar chromophores. When using the stronger 3-methyl-4-cyano-5-dicyanomethylidene-2-oxo-3-pyrroline (TCP) acceptor and replacing the pyrroline nitrogen atom with the same range of X groups, the inductive electron-withdrawing and π-accepting or π-donating characters of X have the same impact on β as in the TCF motif.

We demonstrate top-gate organic field-effect transistors (OFETs) with a bilayer gate dielectric and doped contacts fabricated on shape-memory polymer (SMP) substrates. SMPs exhibit large variations in Young’s modulus dependent on temperature and have the ability to fix two or more geometric configurations when a proper stimulus is applied. These unique properties make SMPs desirable for three-dimensional shape applications of OFETs. The electrical properties of OFETs on SMP substrates are presented and compared to those of OFETs on traditional glass substrates.

Dimers of 2-substituted N,N'-dimethylbenzimidazoline radicals, (2-Y-DMBI)2 (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n-dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS-pentacene), in solution. X-ray data and DFT calculations both indicate a longer C-C bond for (2-Cyc-DMBI)2 than (2-Fc-DMBI)2 , yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D2 ) dissociation and of D2 -to-A electron transfer, D2 reacts with A to form D(+) and A(-) by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D(+) /0.5 D2 redox potentials-the effective reducing strengths of the dimers-vary little within the series (ca. -1.9 V vs. FeCp2 (+/0) ) (Cp=cyclopentadienyl) due to cancelation of trends in the D(+/0) potential and D2 dissociation energy. The implications of these findings for use of these dimers as n-dopants, and for future dopant design, are discussed.

The fundamental limits of inorganic semiconductors for light emitting applications, such as holographic displays, biomedical imaging and ultrafast data processing and communication, might be overcome by hybridization with their organic counterparts, which feature enhanced frequency response and colour range. Innovative hybrid inorganic/organic structures exploit efficient electrical injection and high excitation density of inorganic semiconductors and subsequent energy transfer to the organic semiconductor, provided that the radiative emission yield is high. An inherent obstacle to that end is the unfavourable energy level offset at hybrid inorganic/organic structures, which rather facilitates charge transfer that quenches light emission. Here, we introduce a technologically relevant method to optimize the hybrid structure's energy levels, here comprising ZnO and a tailored ladder-type oligophenylene. The ZnO work function is substantially lowered with an organometallic donor monolayer, aligning the frontier levels of the inorganic and organic semiconductors. This increases the hybrid structure's radiative emission yield sevenfold, validating the relevance of our approach., Hybrid inorganic-organic structures can overcome the limits of inorganic semiconductor light emitting devices but the energy level offset is an obstacle. Here, Schlesinger et al. lower the ZnO work function with an organometallic donor monolayer and enhance the radiative emission of the hybrid structure.

Photonic technologies operate by the optical processing and transmission of information and require a variety of materials with appropriate properties to facilitate the modulation of light. Polymers containing organic nonlinear optical (NLO) chromophores allow the modulation of the phase, the state of polarization, and/or the frequency of light beams, as required for the optical encoding, transmission, and routing of information. Both secondand third-order NLO effects are potentially useful [1]. Materials with large secondand third-order nonlinearities can be useful for the doubling and tripling, respectively, of the frequency of optical signals. They can also be used for routing and switching applications in which NLO effects involving the ability to vary the refractive indices of the materials using an applied electric field are important. The refractive index of second-order NLO materials is dependent on electric field; this effect is known as the linear electro-optic (EO) or Pockels effect. Materials with large EO coefficients can be used for the fabrication of ultrafast low-power EO modulators that can be integrated with electronics. In third-order NLO materials, the refractive index is dependent on the intensity of light and so can bemodulated with an optical control pulse, negating the need to integrate electronics directly with the NLO material and facilitating all-optical modulation, which holds promise for ultrafast signal processing, potentially enabling much higher bandwidth communications. In organic materials with large secondor third-order nonlinearities, these nonlinearities are largely due to the interaction of light with conjugated p-systems. Here a simple model is described that has helped to provide design strategies for the optimization of second-order and third-order nonlinear optical effects in quasi-linear organic molecules.

N-doping of an electron-transport material, a tris(thieno)hexaazatriphenylene derivative ( 1 ), with the strongly reducing molecule bis(cyclopentadienyl)-cobalt(II) (cobaltocene, CoCp 2 ), is investigated using ultra-violet, X-ray, and inverse photoemission spectroscopies, and current–voltage measurements. Condensed CoCp 2 films show a 4 eV ionization energy, which is unusually low for vacuum-deposited molecular material and suggests that cobaltocene is promising as a molecular n-dopant. Efficient n-doping of 1 by CoCp 2 is confirmed by a 0.56 eV shift of the Fermi level toward the unoccupied states of the host, and by a three orders of magnitude current increase in devices where compound 1 is interfacially doped with cobaltocene.

Several new ferrocenylethynyl derivatives, (FcCC)2CHOH, (FcCC)2CH2, (FcCC)2CPhOH have been synthesised from ethynylferrocene. Attempts to synthesise the corresponding bis(ferrocenylethynyl)-stabilised carbocations by hydroxyl or hydride abstraction from the bridging group was unsuccessful for (FcCC)2CHOH and (FcCC)2CH2, respectively. In the case of (FcCC)2CPhOH, the [(FcCC)2CPh]+ cation could be observed by 1H and 13C NMR, and by UV–Vis–NIR spectroscopy, but was too unstable for isolation or prolonged study in solution. The UV–Vis–NIR spectrum of [(FcCC)2CPh]+ is compared to that of the considerably more stable cations, [Fc(CHCH)2CH]+ and [(FcCHCH)2CPh]+.

We report the first structural data for bis(diarylamine) "bipolarons": we have isolated and crystallographically characterized salts of the dications obtained by two-electron oxidation of E-4,4'-bis[di(p-anisyl)amino]stilbene and E,E-2,5-bis{4-[di(p-anisyl)amino]styryl}-3,4-di(n-butoxy)thiophene, [1](2+) and [2](2+) respectively. ESR, NMR, and magnetometry suggest both species have singlet ground states. X-ray structures, together with (1)H NMR coupling constants for [2](2+), indicate geometries in which the bond lengths are shifted toward a quinoidal pattern relative to that in the neutral species, but not to a fully quinoidal extent. In particular, the bond-length alternations across the vinylene bridging groups approach zero. DFT calculations with closed-shell singlet configurations reproduce the observed structures well. Our results indicate that singlet species for which one might expect quinoidal geometries (with differences of ca. 0.1 A between formally single and double bonds) on the basis of a limiting valence-bond representation of the structure can, in fact, show structures with significantly different patterns of bond lengths.

We present an experimental and density functional theory comparison of the geometric structure, electronic characteristics and optical properties of 1,1-dimethyl-2,3,4,5-tetraphenylsilole (I), 1,1-(propane-1,3-diyl)-2,3,4,5-tetraphenylsilole (II), 1,1-dimethoxy-2,3,4,5-tetraphenylsilole (III) and 1,1,2,2-tetramethyl-3,4,5,6-tetraphenyl-1,2-disila-3,5-cyclohexadiene (IV). The molecular structures of II–IV have been determined using X-ray crystallography and are compared to the previously reported structure of I. Many characteristics of IV are significantly different from those of I–III, due to the presence of the additional silicon atom. In contrast to I–III, which have planar central rings, IV has a non-planar ring conformation due to the presence of two approximately tetrahedrally coordinated silicon atoms. Cyclic voltammetry suggests that I–III are reduced at similar potentials to that for tris(8-hydroquinolinato)aluminium and that IV is more readily oxidizable than I–III. Additionally, while IV is non-emissive in both solution and the solid state, the three siloles are fluorescent in the solid state. For the four compounds, we have calculated the intramolecular reorganization energies for electron- and hole-transfer reactions, ionization potentials and electron affinities.

Forumla chem. . The optical spectra of 10 p-phenylene-bridged delocalized intervalence compounds MC 6 H 4 M . - or . + are analyzed using the Koopmans-based method, which considers only transitions from filled orbitals to the singly occupied orbital (SOMO), called Hoijtink type A transitions, and from the SOMO to unoccupied orbitals, Hoijtink type B transitions, and ignores configuration interaction. The radical ions with quinonoid structures, those that form ring-M double bonds with M = C(CN) 2 , NMe 2 , 3-oxo-9-azabicyclo[3.3.1], NPPh 3 , and O when the odd electron of the intervalence oxidation level is removed, are calculated to have the lowest-allowed type B transition lying mostly above the lowest-allowed A transition, with B i - A j decreasing in the order shown from +14 370 to -1390 cm - 1 , and the more intense second-lowest-allowed type B transition B i - A j from +14 940 to +7070 cm - 1 . The five radical anions with benzenoid structures, which form ring-M single bonds with X = CN, CO 2 Me, CHO, C 3 HMeBF 2 O 2 , and NO 2 when the odd electron of the intervalence oxidation level is removed, have a B i - Aj value of the opposite sign that increases in magnitude from -2880 to -17 050 cm - 1 in the order shown. Configuration interaction is of course present in the observed spectra, and the predictions ignoring it mostly overestimate transition energies by 1900-2600 cm - 1 for the quinonoid compounds (but by 450 cm - 1 for the M = C(CN) 2 radical anion), and by 1000-1400 cm - 1 for the benzenoid compounds (2500 cm - 1 for the M = CN radical anion). The very simple Koopmans-based model is useful for considering the optical spectra of these radical ions.

[structure: see text] The first fluorine-substituted hexabenzocoronene has been synthesized and is much more readily reduced than its nonfluorinated analogues. Thin films of this material show columnar order at room temperature, and the charge-carrier mobility measured by the pulse-radiolysis time-resolved microwave conductivity technique is comparable to that of other hexabenzocoronene materials.

The one-pot reaction of K2PtCl4 and various 2-arylpyridines, HC∧N, in a 3:1 (v/v) mixture of 2-ethoxyethanol and H2O at 80 °C for 16 h affords cyclometalated platinum complexes, Pt(C∧N)(HC∧N)(Cl), in high yield. These have been fully characterized and, in one case, the X-ray structure has been determined.

We have synthesised a series of new dinuclear metallocenes [{M(Cp*)(C5H4)}2X] (Cp* = eta5-pentamethylcyclopentadienyl; M = Fe, Co, X = CMe2, SiMe2, GeMe2; M = Fe, X = Si2Me4). For the neutral dicobalt complexes, magnetic susceptibility measurements reveal intramolecular antiferromagnetic interactions of -21 and -14 cm(-1) for SiMe2- and GeMe2-bridged species, respectively, but negligible interaction for the CMe2-bridged compound. In contrast, intervalence charge-transfer (IVCT) data for the mixed-valence monocations of both Fe and Co complexes show electronic coupling to decrease in the order CMe2 > SiMe2 > GeMe2. This suggests that electronic coupling is principally through-space in contrast to results found from previous studies. The IVCT data also show much stronger coupling in the dicobalt species versus their diiron analogues.

New hole-transport monomers have been synthesized in which a 2,7-(diarylamino)fluorene hole-transport functionality is linked through the 9-position of the fluorene bridge to a polymerizable acrylate or norbornene group; these monomers have been polymerized under free-radical and ring-opening metathesis polymerization (ROMP) conditions, respectively. The norbornene monomer has also been copolymerized with a cinnamate-functionalized norbornene; this copolymer can be rendered insoluble through photo-crosslinking of the cinnamate groups under UV irradiation, thus permitting the use of the polymer in organic electronic devices based upon multiple polymer layers. The norbornene monomer has also been copolymerized with dicyclopentadiene to afford insoluble crosslinked films. Time-of-flight studies indicate that the norbornene polymer has a higher hole mobility than the analogous acrylate material, consistent with the predictions of the disorder formalism.

SummaryandConclusions Wehavestudiedthetwo-photonabsorptionpropertiesoftwoacceptor-p-acceptor systems with dioxaborine acceptor unitsusing highly correlated quantum-mechanical simulations, andfoundexcellentagreementwithnanosecondandfemtosecondspectroscopicdata.Intheaccessiblespectralregion,therearetwo significant TPA features. The calculations show that thelarge difference in the nonlinear absorption response of thetwo states involved is a consequence of correlation-inducedoscillatorstrengthredistribution;thisemphasizesthatelectroncorrelation is the key to understanding the factors governingtheTPAresponseinp-conjugatedorganicchromophores.Con-figuration mixing also affects the lowest one-photon excitedstate and, in this way, reduces the overall TPA response thatcanbeachieved.Moreover,wefindstrongindicationsthatTPAintotheone-photonallowedstate(S 1 )ismediatedbychannelsinvolving vibrational sublevels of the ground state, therebysupportingthetheoreticalpredictionsinref.[18] Methodology Detailsregardingthesynthesisofthecompoundsandtheirspec-troscopic investigations are contained in the Supporting Informa-tion.Thespecificvaluesofthefluorescencequantumyieldsdeter-minedforIandIIare68and72%,respectively.Quantum-Chemical Modeling: To calculate the TPA cross-sections,westartfrommoleculargeometriesoptimizedwiththesemiempir-icalAM1Hamiltonian.

Reaction of 1,4-(BBr 2 ) 2 C 6 H 4 with cobaltocene gives a bimetallic cobalt complex with cyclopentadienyl and boratabenzene ligands. Oxidation allows the dicationic dicobalt(III) complex to be isolated; the bis(hexafluorophosphate) salt has been structurally characterized. Variable-temperature magnetic susceptibility measurements on the neutral dicobalt(II) complex showed substantial deviation from the Curie-Weiss law; a fit to the Bleaney-Bowers equation for a singlet ground state and a triplet excited state gave an exchange interaction of J = ca. -28 cm - 1 . Electrochemical studies, as well as near-infrared data on the mixed-valence species, suggest that the interaction between the metal centers is weak.

Bis(dioxaborine)fluorenes (DOB) have been studied as potential electron-transport materials. These materials are reversibly reduced at ca. −1.31 V vs ferrocenium/ferrocene, indicating that they have considerably higher electron affinities than tris(8-hydroxyquinoline)aluminum (AlQ3). They are also highly fluorescent in both solution and the solid state. Time-of-flight measurements show the room-temperature electron mobility of one example to be 2 orders of magnitude higher than the commonly used electron-transport material AlQ3. Organic light emitting diode (OLED) devices based on the dioxaborine and poly(9-vinylcarbazole) have been fabricated and show a red emission that can be attributed to an exciplex or a charge-transfer complex formed between the two organic components. Forster energy transfer from the exciplex or the charge-transfer complex to a phthalocyanine dopant in the dioxaborine electron-transport layer leads to a near-infrared-emitting OLED.

The dehydro[3](1,1′)ferrocenophanes, 1,1′-(1-propene-1,3-diyl)-ferrocene (3a), and 1,1′-(3-phenyl-1-propene-1,3-diyl)-ferrocene (3b) were synthesised under Shapiro conditions from the tosylhydrazones of the corresponding α-oxo-[3](1,1′)ferrocenophanes. Electrochemistry shows 3a is oxidised at smilar potential to ferrocene; according 3a can be chemically oxidised using silver trifluoromethanesulfonate. The structure of 3a shows a ring tilt of 11.3°. Attempts to polymerise 3a using the ROMP initiator Mo(CHCMe2Ph)[N(2,6-iPr2C6H3)][OCMe(CF3)2]2 led to a mixture of insoluble material and a soluble mixture of apparently cyclic oligomers ([3a]n).

A series of new thiophene-bridged chromophores based on the powerful heterocyclic acceptor 3-(dicyanomethylene)-2,3-dihydrobenzothiophene-1,1-dioxide has been synthesized; the dependence of the linear and second-order nonlinear optical properties and thermal stability of these species upon the donor group and the bridging group have been studied. In addition, the synthesis of a related new acceptor, not containing the fused benzene ring, is described and a chromophore based upon this acceptor is studied.

We report on photocrosslinkable hole-transport polymers and their use as photodefinable hole-transport layers in organic light-emitting diodes. The polymers were obtained by copolymerization of bis(diarylamino)biphenyl-based acrylate monomers with cinnamate-functionalized acrylate moieties. Polymers with a range of redox potentials were obtained by varying the substitution patterns of the bis(diarylamino)biphenyl units. The 2 + 2 cycloaddition of the cinnamate moieties following UV irradiation renders the material insoluble. This allows for patterning of the polymer and simultaneously enables the fabrication of multilayer structures from solution. Hole mobilities were measured in these copolymers with the time-of-flight technique. Their performance as hole-transport layers in light-emitting diodes, with tris(8-hydroxyquinolinato)aluminum as the emitter and electron-transport layer, is evaluated. Electroluminescent devices with multiple hole-transport layers having different ionization potentials were fabricated from solution, and the quantum efficiency of these devices was greater than that for devices based on a single hole-transport layer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2726–2732, 2003

A series of chromophores with high second-order nonlinearities has been synthesized; the chromphores consist of triarylamine or dialkylarylamine donors linked by a conformationally locked polyene bridge to a dicyanomethylidene acceptor. The use of bridges of this type, combined with the replacement of dialkylarylamine with triarylamine donors, leads to high thermal stability without adverse affects on the nonlinear optical properties of the chromophores.

The effect of substitution on hole mobility in N,N‘-bis(m-tolyl)-N,N‘-diphenyl-1,1‘-biphenyl-4,4‘-diamine (TPD) derivatives doped in polystyrene was studied using the time-of-flight technique. Mobility data were collected as a function of electric field and temperature to yield the energetic and positional disorder parameters defined in the disorder formalism. Substituted derivatives exhibit lower mobilities than regular TPD. This decrease is influenced by the change in dipole moment upon substitution of the molecule. However, the dipolar disorder contribution is found to account only partially for the large differences in mobility.

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.

This study investigates electron transport and distribution of an organometallic dimer-based dopant (RuCp*Mes)2 in benchmarked P(NDI2OD-T2) films, in which electron transport is not affected by deep traps originating from atmospheric contaminants. The electron mobility of P(NDI2OD-T2) can be enhanced by >10‚ in diodes with reduced thermal activation energy using (RuCp*Mes)2 dopants, which is rationalized by the filling up of tail electronic states by doping induced carriers. n-doping with (RuCp*Mes)2 can also improve electron injection at Schottky contacts in nanoscale transport measurements confirmed by conducting atomic force microscopy. The results suggest that the (RuCp*Mes)2 dopants are homogenously distributed throughout the P(NDI2OD-T2) film, at least laterally, at moderate doping concentrations. Thus, these results demonstrate an opportunity of using air-stable molecular n-doping to modulate charge transport properties for solution-processed organic optoelectronic devices.

Doping of graphene is a viable route toward enhancing its electrical conductivity and modulating its work function for a wide range of technological applications. In this work, the authors demonstrate facile, solution-based, noncovalent surface doping of few-layer graphene (FLG) using a series of molecular metal-organic and organic species of varying n- and p-type doping strengths. In doing so, the authors tune the electronic, optical, and transport properties of FLG. The authors modulate the work function of graphene over a range of 2.4 eV (from 2.9 to 5.3 eV)—unprecedented for solution-based doping—via surface electron transfer. A substantial improvement of the conductivity of FLG is attributed to increasing carrier density, slightly offset by a minor reduction of mobility via Coulomb scattering. The mobility of single layer graphene has been reported to decrease significantly more via similar surface doping than FLG, which has the ability to screen buried layers. The dopant dosage influences the properties of FLG and reveals an optimal window of dopant coverage for the best transport properties, wherein dopant molecules aggregate into small and isolated clusters on the surface of FLG. This study shows how soluble molecular dopants can easily and effectively tune the work function and improve the optoelectronic properties of graphene.

Top-gate bottom-contact field-effect transistors based on solution-processed films of molecules in which two naphthalene-1,8:4,5-bis(dicarboxdiimide)s are bridged by thieno[3,2-b]thiophene, dithien...

The dimers of some Group 8 metal cyclopentadienyl/arene complexes and Group 9 metallocenes can be handled in air, yet are strongly reducing, making them useful n-dopants in organic electronics. In this work, the X-ray molecular structures are shown to resemble those of Group 8 metal cyclopentadienyl/pentadienyl or Group 9 metal cyclopentadienyl/diene model compounds. Compared to those of the model compounds, the DFT HOMOs of the dimers are significantly destabilized by interactions between the metal and the central CC σ-bonding orbital, accounting for the facile oxidation of the dimers. The lengths of these CC bonds (X-ray or DFT) do not correlate with DFT dissociation energies, the latter depending strongly on the monomer stabilities. Ru and Ir monomers are more reducing than their Fe and Rh analogues, but the corresponding dimers also exhibit much higher dissociation energies, so the estimated monomer cation/neutral dimer potentials are, with the exception of that of [RhCp2 ]2 , rather similar (-1.97 to -2.15 V vs. FeCp2 (+/0) in THF). The consequences of the variations in bond strength and redox potentials for the reactivity of the dimers are discussed.

An efficient protocol for the double symmetrical arylation using aryl bromides, one-pot or sequential arylation using two different aryl bromides or monoarylation of difluorobenzothiadiazole is developed.

By preventing aggregation of polymethine molecules at high number density, we have developed organic materials with large third-order nonlinearities and low nonlinear absorption in the near-infrared thereby enabling demonstration of an all-optical signal processing application.

Four compounds have been studied which contain ferrocene or octamethylferrocene donors linked by CH 2 bridges to cobaltocenium or pentamethylcobaltocenium acceptors. The electronic spectra of these compounds cannot be accounted for by superposition of those of the constituent metallocenes; in each case, a low-energy solvatochromic absorption is observed, the energy of which parallels the difference in electrode potentials between the iron and cobalt centers. This absorption is assigned to Fe I I -to-Co I I I charge transfer; analysis using Hush theory gives delocalization parameters V and a in the ranges 46-130 meV and 0.019-0.069, respectively, indicating much stronger coupling between the metal centers than in structurally similar ferrocene/ferrocenium systems.

We investigate by means of gas-phase ultraviolet photoelectron spectroscopy complemented by quantum-chemical calculations how the frontier levels of the 4,4‘-bis(N-m-7tolyl-N-phenylamino)biphenyl (TPD) molecule are affected upon substitution of the terminal aryl rings with methoxy groups or fluorine atoms. These results provide strategies to modulate energy barriers at metal/organic or organic/organic interfaces involving TPD and its derivatives; it is shown that the change in the energy of the HOMO level of TPD upon derivatization is strongly affected by inductive effects taking place in the σ skeleton.