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A recently developed combinatorial method utilizing angular dependence of evaporation rate was used to create compositional spread thin film libraries of Tris(2-pyridin-2-yl-indolizino[3,4,5-ab] isoindole-C(1), N('))iridium(III) [Ir(pin)(3)] and 4,4(')-N,N(')-dicarbazol-biphenyl (CBP) composite, with the molar fraction of Ir(pin)(3) complex varying in the 0.0003chi(Ir(pin)(3) )0.96 range. Spatially correlated absorbance and photoluminescence (PL) measurements were used to quantify luminescence quenching of photo-excited CBP molecules by the Ir(pin)(3) complex as a function of the average distance between two molecules. It was found that the CBP--Ir(pin)(3) energy transfer proceeds by the Forster mechanism with the Forster radius of 30 A. The CBPxIr(pin)(3) composite has the highest photoluminescence quantum efficiency approximately 0.95, for chi(Ir(pin)(3) )=0.03 and is characterized by a structured green emission (lambda(max)=538 nm) originating from the ligand-centered (pi-pi(*))(3) state of the Ir(pin)(3) complex. On the contrary, the PL spectra of Ir(pin)(3) bulk are characterized by a weak red emission (lambda(max)=673 nm) attributed to the lowest metal-to-ligand charge transfer state. A statistical analysis based on a binomial distribution indicates that the emission from the (pi-pi(*))(3) state is quenched in Ir(pin)(3) molecules that are in a direct contact with each other.

We report steady-state photo-induced absorption (PIA) and photo-induced reflectance (PIR) in films of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and poly[2,5-bis cholestanoxy-1,4 phenylene vinylene] (BCHA-PPV) blended with fullerenes. Absorption from the metastable charge-transferred state is probed by PIA; the modulated absorption spectrum causes changes in the real part of the index of refraction, Δn, which can be measured directly by PIR. The charge transfer gives rise to pronounced features in Δn, including vibrational structure in the mid-infrared, and broad spectral windows with negative Δn in the mid- and near-infrared. Our measurements over a wide spectral range (0.05 eV–1.9 eV) allow quantitative comparison of Δn obtained from PIR with that obtained from Kramers–Kronig transformation of the PIA data. We find good agreement throughout the infrared, indicating that our method for measuring Δn is useful as an analytical tool for optical characterization and for prediction of optical spectral ranges for nonlinear optical response.

The photoinduced electron transfer between conjugated polymers and a series of functionalized fullerenes was studied. A new photoluminescence signal was observed in the near IR (∼1.4 eV). This weak IR photoluminescence does not result from direct excitation of the fullerene, but from radiative electron-hole recombination between the fullerene excited state and the polymer ground state. The intensity of this recombination luminescence depends on the electrochemical nature of the functional group; it is observed only for fullerenes with first reduction potential higher than that of C60.

We report the fabrication of polymer grid triodes (PGTs) using C60 as the semiconducting medium. The structure, a self-assembling porous conducting polyaniline network placed between two semiconducting layers of C60, and sandwiched between two metal electrodes, demonstrates the I–V characteristics of a three terminal device in which the current is controlled by the grid potential. As a result of the higher mobilities of the fullerenes compared to those of conjugated polymers, the fullerene devices offer some performance advantages; the operating voltages are less than 5 V with current densities exceeding 1 mA/cm2. By fabricating devices with different grid densities, it is shown that the grid exhibits a strong influence on the I–V characteristics for high grid densities, and a correspondingly low influence for low densities, in agreement with theory. The I–V characteristics of the C60 PGTs are well described by an effective diode model, similar to that used for vacuum triodes.

Bright, efficient, and stable white polymer light-emitting diodes based on blue polyfluorene doped by a “twistacene,” 6, 8, 15, 17-tetraphenyl-1.18, 4.5, 9.10, 13.14-tetrabenzoheptacene (3) (TBH), are demonstrated. In “twistacene” the terminal pyrene moieties serve two functions: (i) to stabilize the inherently unstable heptacene and (ii) to enable the oligoacene to be a strongly fluorescent molecule. As a result, efficient and very bright white polymer light-emitting diodes are obtained. The maximum luminance of the devices exceeds 20000cd∕m2. The maximum luminous efficiency is 3.55cd∕A at 4228cd∕m2 while the maximum power efficiency is 1.6lm∕W at 310cd∕m2. The device obtains a stable white balance by a combination of energy transfer from the blue polyfluorene to TBH by 1% TBH doping plus the host emission. The device emission color is not a function of bias current, which is ideal for various applications, from lighting to the backlight for liquid crystal displays.

Near-steady-state photoinduced absorption (PIA) and photoluminescence studies are presented on photoinduced electron transfer reactions from poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and poly[3-(2-(3-methylbutoxy)ethyl)thiophene] (P3MBET) as donors (D) onto a homologous series of tetracyano-p-quinodimethane (TCNQ) derivatives containing fused aromatic rings as acceptors (A) to systematically study the effect of acceptor electron affinity. We observe that composite films of these D/A couples give rise to long-lived charge separated states upon photoexcitation, as evidenced from the formation of polaron bands (radical cation absorption) in the PIA and the concomitant loss of the metastable triplet PIA and photoluminescence that are observed in pristine MEH-PPV and P3MBET. We find that the efficiency of the photoinduced electron transfer reaction correlates with the reduction potential of the acceptors.

We present near-steady-state photoinduced absorption (PIA), photoluminescence, and light-induced electron spin resonance (LESR) studies on photoinduced electron transfer reactions from poly(bis-2,5-epi-cholestanoxy-1,4-phenylene vinylene) (BeCHA-PPV) as a donor to Buckminsterfullerene (C60) and a number of functionalized fullerenes as acceptors. We show that functionalized fullerenes with a solubilizing side chain linked to C60 in a [5,6] (fulleroid) or [6,6] (methanofullerene) fashion, are efficient electron acceptors towards BeCHA-PPV, as evidenced from changes in the PIA, the efficient quenching of the photoluminescence, and the LESR spectra of BeCHA-PPV cation and fullerene anion radicals. The increased miscibility of the functionalized fullerenes with the conjugated polymer as compared to C60, can be important for the preparation of future electrooptic devices, based on the photoinduced charge separation.

We report the results of initial measurements on two derivatives of poly(1,6‐heptadiyne): a di‐ketone (PHDK) and a di‐ester (PHDE). Both polymers have the degenerate ground state of poly(1,6‐heptadiyne); both are soluble in common organic solvents. Electron spin resonance (ESR) measurements on pristine samples place an upper limit of 10−4 spins per monomer for both polymers. At low doping levels, we observe a single doping‐induced absorption band at an energy of approximately half the π−π* gap, Eg/2; the doping‐induced spectral features were fully reversible. In situ ESR and absorption measurements during doping show that charge is stored predominantly in spinless charge carriers. Because of the inequivalent carbons on the conjugated backbone, the results are discussed in terms of the (A=B)n polymer. Both PHDK and PHDE are relatively stable in air; the strength of the π−π* absorption band is nearly constant over a period of a week in air, decreasing to 80% of the initial value.

A hybrid inkjet printing (HIJP) technology, which combines a pin-hole free polymer buffer layer and an inkjet printed polymer layer, allows the patterning of high quality polymer light-emitting devices. In this letter, we present a successful demonstration of controllable patterning of dual-color polymer light-emitting pixels using this HIJP technique. In this demonstration, the polymer buffer layer is a wide band gap, blue emitting semiconducting polymer prepared by the spin-casting technique. The inkjet printed layer is a red-orange semiconducting polymer which was printed onto the buffer layer. When a proper solvent was selected, the printed polymer diffused into the buffer layer and efficient energy transfer took place generating a red-orange photoluminescence and electroluminescence from the inkjet printed sites. Based on this principle, blue and orange-red dual-color polymer light-emitting pixels were fabricated on the same substrate. The use of this concept represents an entirely new technology for...

Nonlinear optical absorption in solid films of poly(3‐octylthiophene) (P3OT) sensitized with methanofullerene was investigated for wavelengths from 620 to 960 nm. The nonlinear absorption is enhanced over that in either of the component materials by more than two orders of magnitude at 760 nm. The large nonlinearity results from efficient photoinduced intermolecular charge transfer from P3OT to methanofullerene, followed by absorption in the charge separated excited state. P3OT/fullerene films are promising as optical limiters; the transmission clamps at an average fluence of approximately 0.1 J/cm2. The damage threshold was 15 μJ/pulse (≊1 J/cm2 in average fluence), above which there is a permanent change in the linear transmission.

The characterization of rectifying heterojunctions (diodes) fabricated from a semiconducting polymer, a soluble derivative of poly(phenylene‐vinylene), and buckminsterfullerene, C60, are reported. Rectification ratios in the current versus voltage characteristics exceed 104. When illuminated, the devices exhibit a large photoresponse as a result of photoinduced electron transfer across the heterojunction interface from the semiconducting polymer (donor) onto C60 (acceptor). The photodiode and photovoltaic responses are characterized. Photoinduced electron transfer across the donor‐accepted rectifying heterojunction offers potential for photodetector and for solar cell applications.

The authors demonstrate the operation of an organic single-crystal complementary circuit in the form of a simple inverter. The device is constructed from a high mobility p-type organic single-crystal transistor of tetramethylpentacene (TMPC) and a n-type single-crystal transistor of N,N′-di[2,4-difluorophenyl]-3,4,9,10-perylenetetracarboxylic diimide (PTCDI). Field-effect mobilities of up to 1.0cm2∕Vs are reported for TMPC devices, while a mobility of 0.006cm2∕Vs is reported for a n-type PTCDI single-crystal device. Considering that organic single-crystal inverters have not yet been explored, they are representative of potential candidates for use in high-performance complementary circuits.

A twofold absolute photoluminescence quantum yield (PLQY) enhancement of poly(2-methoxy 5-[2′-ethylhexyloxy]-p-phenylenevinylene) (MEH-PPV) is demonstrated by simple preparation of films where the polymer is blended with the small organic molecule 7,8,10-triphenylfluoranthene (3PF). The photophysical investigation of this particular energy transfer process was carried out using steady state absorption/luminescence spectroscopy and optically detected magnetic resonance techniques. The enhanced PLQY is attributed to direct sensitization of the intrachain emitting state of MEH-PPV by energy transfer from 3PF.

We report an organic, nonvolatile memory based on dopant concentration-induced conductance changes in a conjugated polymer. Consisting of a polymer poly [2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV)/ionic conductor (RbAg4I5) bilayer sandwiched between two metal electrodes, the device is electrically switched between its low-conductance “off” state and high-conductance “on” state reversibly and repeatedly with on/off ratios above two orders of magnitude and pulse durations as short as 1μs when a voltage exceeding its threshold values (>+3.5V or

We present valence effective Hamiltonian (VEH) band‐structure calculations on polyisothianaphthene and some of its simple derivatives. Our goal is to rationalize the lowering of the band gap by about 1 eV which is experimentally observed in polyisothianaphthene (Eg=∼1 eV) relative to the parent polymer, polythiophene (Eg=∼2 eV). We show that the smaller band gap found in polyisothianaphthene can be understood on the basis of a relationship which can be established between the band gap energy and the importance of the effective quinoid contributions to the electronic structure. Our theoretical results also indicate that simple dimethyl, dimethoxy, or dicyano substitutions are not expected to affect the size of the band gap in any significant way.

Preparation and some properties of tetramethyldithiadiselenafulvalene (TMDTDSF) are described. It forms the expected (donor)2 X salts. Properties of the PF−6 salt are described as well as properties of alloys of the title compound with tetramethyltetraselenafulvalene (TMTSF). (TMDTDSF)2PF6 is a relatively poor conductor even though it is isomorphous with the high‐pressure superconductor (TMTSF)2PF6. The profound difference in properties between these two solids is ascribed to disorder in the arrangement of sulfur and selenium atoms along the donor stacks in (TMDTDSF)2PF6. Alloying very small amounts of TMDTDSF into (TMTSF)2PF6 causes the metal‐to‐insulator transition temperature (TMI) to move up smoothly from 11 K for pure (TMTSF)2PF6 to ∼200 K for pure (TMDTDSF)2PF6 due to increasing disorder as TMDTDSF is incorporated.

Geometry optimizations and band structure calculations are reported on two polymeric vinylene derivatives of pyrene: poly(1,6‐pyrenylene vinylene) and poly(2,7‐pyrenylene vinylene). The results are indicative of a dramatic sensitivity of the electronic structure on the mode of connection of the two vinylene units to the pyrene rings, in agreement with the chemist’s intuition. An analysis of the atomic π orbital contributions to the one‐electron wave functions shows that the HOMO–LUMO characteristics of both compounds are markedly different. The 1‐6 mode of connection leads to an electronic structure similar to that of polyparaphenylene with a bandgap of 2.9 eV. The 2‐7 mode of connection results in a significantly lower bandgap, around 1.7 eV, due to the stabilization of quinoid resonance structures.

The solid state physical properties of an isomorphous series of TTF salts (TTF11 (SCN)6, TTF11 (SeCN)6, and TTF7I5) were examined. While there was no noticeable trend in the conductivity (as a function of temperature and anion), the effective Fermi energy (?F) and the magnetic susceptibility transition temperature exhibited a definite trend as a function of anion. There is a correlation between the above properties and subtle variations in solid state structure of each of the above salts.

High resolution x‐ray photoelectron spectra are presented for tetrathiotetracene, tetrathionaphthalene, and tetraselenotetracene. C1s and S2p core levels and their shake‐up satellites, as well as valence band spectra, are related with molecular geometry to give a detailed picture of electronic structure and bonding. The model is applied to the semiconducting properties of these solids compared to those of their complexes with electron acceptors, and those of the corresponding acenes, shedding light on the particular role of the disulfide (or diselenide) groups.

The physical and electronic properties of poly(isothianaphthene) PITN, are reported, including initial characterization, electrochemical cyclic voltammetry, spectroscopy, and transport properties. PITN has the smallest energy gap of any known conjugated organic polymer, Eg≂1 eV. This novel conjugated polymer exhibits reversible chemical and electrochemical p‐type doping with an associated high contrast color change. After doping, thin films of PITN have very low optical density in the visible portion of the spectrum. Thus, PITN is the first example of a transparent highly conducting polymer (σ∼50 Ω−1 cm−1).

The solid state properties of the title compound are described. The material undergoes a metal to insulator transition at 86 K which is not driven by spin density waves. The metal to insulator transition is reflected by very sharp changes in conductivity and magnetic susceptibility.

The electrochromic performance of all solid‐state cells employing phosphotungstic acid and phosphomolybdic acid is reported. These cells employ SnO2 as the viewing electrode and graphite as the back electrode. Diffuse reflectivity changes of ∼50% are readily achieved in ∼10 msec. The cells, in the bleached state, can be made white to red, and become black in the colored state.

The spin resonance of holes in the single‐stack organic conductor (TMTSF)2PF6 is readily observed from room temperature down to ∼l2 K with monotonically decreasing linewidth. Below that temperature no signal is observed at low microwave power but if the sample is exposed to microwave electric fields parallel to the needle axis the resonance reappears suddenly at higher microwave power. The threshold power for spin ’’resurrection’’ rises on cooling below 12 K and, in samples of improved purity, a second threshold marked by a distinct change in line shape appears below ∼9 K. These nonlinear magnetic effects are also accompanied by sharp but weak changes in the sample’s loading of the microwave cavity and may be qualitatively correlated with a decrease in DC conductivity accompanied by nonlinear electric‐field response, as well as anomalous variations of the magnetic susceptibility. These results suggest a spin‐density‐wave ground state which is very easily disturbed by experimental probes.