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1997
Exciplex emission in heterojunctions of poly(pyridyl vinylene phenylene vinylene)s and poly(vinyl carbazole).
Synthetic Metals,vol.85,p.1205–1208,1997Photoluminescence and electroluminescence spectra were obtained, of heterojunctions formed from poly(vinyl carbazole) (PVK) and poly(pyridyl vinylene phenylene vinylene) (PPyVPV) conjugated polymers. Bilayers of PVK and PPyVPV show a photoluminescence peak which cannot be assigned to either the PVK or the PPyVPV layer. Absorption spectra show that the addnl. feature results from an exciplex at the bilayer interface. The electroluminescence spectrum from the heterojunctions is due to exciplex emission, with internal efficiency of ∼0.1-0.5%. [on SciFinder(R)] -
1997
Light-emitting devices based on pyridine-containing conjugated polymers.
Synthetic Metals,vol.85,p.1179–1182,1997The emitting properties of polypyridine and various copolymers were measured and prototype light-emitting devices based on pyridine-contg. conjugated polymers and copolymers were assembled in various configurations. The high electron affinity of pyridine based polymers enables the use of relatively stable metals such as Al or even ITO as electron injecting contacts. Bilayer devices utilizing poly(9-vinyl carbazole) (PVK) as hole transporting/electron blocking polymer were assembled, which show improved efficiency and brightness, due to charge confinement and exciplex emission at the PVK/emitting polymer interface. The incorporation of a conducting polyaniline network electrode in the PVK structure, lowers the device turn-on voltage significantly while maintaining high efficiency. Control of aggregate formation in the polymer films by blending with insulating host polymers [PMMA] opens up the possibility of making voltage-controlled multi-color light-emitting devices. [on SciFinder(R)] -
1997The low energy photophysics of the pyridine-based polymers poly(p-pyridine)(PPy), poly(p-pyridylvinylene) (PPyV) and copolymers made up of PPyV and poly(p-phenylenevinylene) (PPyVPV). The absorption and luminescence properties are morphol. dependent. The primary photoexcitations within these polymers are singlet excitons which may emit from individual chains following a random walk to lower energy segments, depending upon the excitation energy. Films display red shifted absorption and emission properties with a decrease in photoluminescence efficiency which can be attributed to aggregate formation in comparison to powder and soln. forms. Photoinduced absorption (PA) studies show direct conversion of singlet to triplet excitons on the ps time scale. Polaron signatures and the transition between triplet exciton states are seen in powder forms using ms PA techniques. Film forms display only a polaron signature at millisecond times indicating that morphol. plays a key role in the long-time photophysics for these systems. Photoluminescence detected magnetic resonance studies also have signatures due to both polarons and triplet excitons. The size of the triplet exciton is limited to a single ring suggesting that the triplet exciton may be trapped by extrinsic effects. [on SciFinder(R)]
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1997
Alternating poly(pyridyl vinylene phenylene vinylene)s: synthesis and solid state organizations.
Tetrahedron,vol.53,p.15487–15494,1997Poly(pyridylvinylenephenylenevinylenes) were synthesized by Heck coupling procedures. These materials display large red shifts in their optical absorption which upon protonation of alkylation of the pyridyl nitrogen. Some of the polymers were found to be liq. cryst. The protonated or alkylated versions exhibit highly organized structures due to charge-transfer interactions between polymer chains. [on SciFinder(R)] -
1996
Design of conducting redox polymers. A polythiophene-Ru(bipy)3n+ hybrid material.
Advanced Materials (Weinheim, Germany),vol.8,p.497–500,19965,5′-Bis(2”-bithiophene)-2,2′-bipyridine ligand (L) and its Ru complex [Ru(L)3(PF6)2] were synthesized and underwent polymn. upon electrochem. oxidn. The resultant polythiophene-Ru(L)3n+ hybrid material displayed both the conducting properties of the polymer and the redox properties of the isolated metal centers which was shown by cyclovoltammetry. [on SciFinder(R)] -
1996
Chiral Metallocalix[4]arenes: Resolution by Diastereomeric Tungsten(VI) Alkoxides
Angewandte Chemie, International Edition,vol.35,p.2094–2097,1996The chiral metallocalix[4]arene [W(L)Cl2] (L = 3,4-dimethylcalix[4]arene) was resolved by means of tungsten alkoxide complex prepn. The dichloride was reacted with (1S,2S)-trans-1,2-cyclohexanediol or (S,S)-(-)-hydrobenzoin to give the substituted complexes. The hydrobenzoin complex diastereomers were more easily sepd. than those of the cyclohexanediol complex and were converted back to the dichlorides or to the oxides [WO(L)] as pure enantiomers. The CD spectra of the thus prepd. [W(L)Cl2] complexes are mirror images, confirming that they are enantiomers. [on SciFinder(R)] -
1996
Tungsten and molybdenum oxo complexes of tetrakis(phenyldiazenyl)calix[4]arene substituted derivatives: EHMO calculations, spectroscopic characterization, and perturbations of the photophysical properties by neutral guest molecules.
Canadian Journal of Chemistry,vol.74,p.2279–2288,1996Bowl-shaped chromophores fabricated with tungsten and molybdenum oxo complexes of calix[4]arenes substituted at the para positions with phenyldiazenyl (R2C6H3N2) derivs. are investigated. The nature of the lowest energy excited states has been addressed theor. using EHMO calcns. and exptl. using UV-visible, luminescence, and polarized emission spectroscopy at 77 K. The lowest energy excited states are intraligand (azobenzene fragment) $π$$π$* (S2 and T2) and n$π$* states (S1 and T1). The compds. are weakly luminescent in the 600-630 nm range exhibiting emissions arising from the 1($π$$π$*) states (S2 → S0, 1 < $tau$e < 4 ns, and 3 × 10-3). The region located above 900 nm was not investigated. Evidence for guest-host chem. has been demonstrated by 1H-NMR spectroscopy, and the binding consts. for two of the compds. with pyridine in toluene as a solvent were obtained by UV-visible spectroscopy. The presence of a guest mol. inside the luminescent metal oxo complex of a calix[4]arene hosts decreases the emission lifetimes. [on SciFinder(R)] -
1996
Stabilization of Nondiscoid Columnar Liquid Crystals: Studies of Unsymmetrical Copper Bis-$beta$-diketonates.
Chemistry of Materials,vol.8,p.907–911,1996Cu(bis-$beta$-diketonate) complexes are reported which display columnar liq.-crystal phases with a hexagonal disordered structure (Dhd). The complexes do not have the disk-shape characteristic of most Dhd materials, but produce a disk shape by forming dimers with 90° rotations between nearest neighbors. In the liq.-cryst. state this dimerized nature produces short-range rotational correlations. Three side-chain Cu bis-$beta$-diketonates with a single Ph substituent are not liq. cryst., and an extension of the mesogenic core is necessary to introduce liq. crystallinity. The simple Ph analogs are monotropic, and the addn. of electron-withdrawing substituents to the Ph moiety results in a stabilization of the mesophase. These substituents produce favorable dipolar interactions which stabilize the mesophase. Consistent with this explanation, electron-donating substituents are not effective at stabilizing the mesophase. Substitution of the complex with thiophene groups rather than phenyls produces stable mesophases with greatly lowered melting and clearing points. This latter result indicates that thiophene substitution provides dispersive forces which destabilize the crystal phase. Thiophene substitution may provide a general method for reducing transition temps. in metallomesogens. [on SciFinder(R)] -
1996
3-Methylcalix[4]arene: A New Versatile Precursor to Inherently Chiral Calix[4]arenes.
Journal of Organic Chemistry,vol.61,p.802–804,1996This paper describes the first synthesis of 3-methylcalix[4]arene, an inherently chiral mol. which can be readily functionalized. The procedure involves hydromethylation of the readily available 4-bromo-3-methylphenol followed by dehydrative cyclization with TiCl4 to give 4-bromo-3-methylcalix[4]arene. Debromination proceeds in near quant. yield to give the targeted 3-methylcalix[4]arene-25,26,27,28-tetrol. 3-Methylcalix[4]arene undergoes reactions at the para position to give functionalized chiral calix[4]arenes in good to excellent yields. [on SciFinder(R)] -
1996
Conducting Polymetallorotaxanes: A Supramolecular Approach to Transition Metal Ion Sensors.
Journal of the American Chemical Society,vol.118,p.8713–8714,1996Two metallo-rotaxane complexes, assemble when the macrocyclic phenanthroline and Cu+ or Zn2+ ions are combined in CH2Cl2. Anodic electrochem. polymn. produce the corresponding polymetallorotaxanes. Electrochem. investigations indicate that the conductivities of the polymers exhibit redox-like profiles. It was demonstrated that the polyrotaxane structure reversibly bind Zn2+ ions, thereby confirming the potential of the structures as sensory materials. [on SciFinder(R)] -
1996
Equilibrium Flexibility of a Rigid Linear Conjugated Polymer.
Macromolecules,vol.29,p.7323–7328,1996The unusual electronic and optical properties of many electroluminescent and conducting polymers arise from extended conjugation along the polymer backbone, which can also lead to insoly., aggregation, and gelation. Synthetic efforts to produce an optimal structure require a balance between the persistence length and the effective conjugation length for the successful implementation of these materials in photonic and electronic devices. The soln. properties of a group of poly(phenyleneethynylenes) were investigated using a variety of light scattering techniques, including polarized and depolarized intensity measurements, dynamic light scattering, and size exclusion chromatog. with a multiangle light scattering detector (SEC/LS). Interpretation of light scattering in the presence of absorption, fluorescence, and optical anisotropy is discussed. The mol. wts. detd. by light scattering encompassed the range from 10 × 105 to 5 × 106, with the root-mean-square radius of gyration as high as 250 nm. The results may be interpreted with a wormlike chain model to yield a persistence length of about 15 nm, so that these high-M polymers are coil-like in soln., rather than rigid rods. This persistence length is still expected to be several times larger than the effective conjugation length. [on SciFinder(R)] -
1996
Metallomesogens: Synthesis Properties, and Applications edited by J. L. Serrano.
Molecular Crystals and Liquid Crystals Science and Technology, Section A: Molecular Crystals and Liquid Crystals,vol.289,p.317–318,1996 -
1996
Photoluminescence in pyridine-based polymers: role of aggregates.
Physical Review B: Condensed Matter,vol.54,p.9180–9189,1996The morphol. dependence of the photoluminescence (PL) properties of the pyridine-based polymers, poly(p-pyridylvinylene), poly(p-pyridine), and poly(p-pyridylvinylene-p-phenylenevinylene) (PPyVPV) was studied. The photoluminescence of soln. samples is characterized by high quantum efficiency (>70% in PPyVPV), weak coupling to vibrational modes (Huang-Rhys parameter ∼0.5) and a single-exponential decay (radiative lifetime ∼1 ns). On the other hand, film samples display strongly red shifted, featureless emission with low quantum yield (<20%) and highly nonexponential decay dynamics. Through consideration of absorption and excitation spectra, the "site-selectivity" of the PL, and the concn. dependence of the PL spectrum, we demonstrate that the red shifted film spectra are a result of the formation of low-energy aggregate sites due to strong interchain interactions. Time-resolved measurements suggest a longer radiative lifetime for the aggregate vs. soln., leading to the lower efficiency. Aggregate formation is morphol. dependent, and is minimal in "powder" samples which are pptd. after polymn. [on SciFinder(R)] -
1996
Spatially and temporally resolved emission from aggregates in conjugated polymers.
Physical Review B: Condensed Matter,vol.54,p.R3683–R3686,1996The authors present results of cw, time-resolved, and spatially resolved spectroscopic studies of emission and absorption in a model conjugated polymer, poly(p-pyridyl vinylene) (PPyV). The red shifted film spectra suggest the formation of aggregated regions. The ∼4X redn. in emission efficiency in films vs. soln. is attributed to a longer radiative lifetime for aggregate excitons, as is evidenced by time-resolved fluorescence measurements. The authors present direct optical imaging of aggregates in a conjugated polymer via near-field scanning optical microscopy. The aggregate emission and absorption are localized to partially aligned regions of the film ∼200 nm in size. [on SciFinder(R)] -
1996We present results of picosecond photoinduced absorption (PA) and time-resolved photoluminescence studies on solid and soln. forms of poly(p-pyridylvinylene). The nearly identical PA response of all forms of the polymer reflects the generation of the same primary photoexcitation, a Couloumbically bound intrachain singlet exciton, and the absence of exotic species such as interchain excimers. The time dependence of the PA points to direct intersystem crossing as the origin of triplet excitons, ruling out generation of free carriers as a precursor to exciton formation. [on SciFinder(R)]
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1996
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1995
Synthesis of regioregular poly(methylpyridinium vinylene). An isoelectronic analog to poly(phenylenevinylene).
Advanced Materials (Weinheim, Germany),vol.7,p.145–147,1995The prepn. of head-to-head (I), head-to-tail (II), and random (III) regioisomeric forms of the title compd. is described. Electrochem. data from cyclic voltammograms are reported. Methylation to give the quaternary regioisomers resulted in a decrease in cond. for the reduced forms of I and III isomers (to <10-7 S/cm). The quaternary II isomer had a cond. of ~{}2.5 x 10-5 S/cm. [on SciFinder(R)] -
1995
Electroluminescent properties of self-assembled polymer thin films.
Advanced Materials (Weinheim, Germany),vol.7,p.395–398,1995A novel class of photo- and electroluminescent polymers (poly(p-pyridyl vinylene), poly(p-pyridinium vinylene), and their butyl-substituted analogs), and their application in org. light emitting devices (OLED) are reported. Polymer thin films for OLEDs were prepd. by both spin coating and a new self-assembly technique on a variety of substrates. They exhibit good fluorescence quantum yields, and the Bu derivs. are sol. in org. solvents. A device consisting of a 50-nm poly(p-phenylenevinylene) layer as hole conductor between the In/Sn oxide-coated glass support and the Bu poly(p-pyridyl vinylene) film and capped with an Al cathode operates with good quantum efficiency (5 × 10-4 photons/electron) for several hours. [on SciFinder(R)] -
1995
Lyotropic polymorphism in oxovanadium complexes.
Advanced Materials (Weinheim, Germany),vol.7,p.280–283,1995Oxovanadium-based surfactants which display binary (surfactant/H2O) and ternary (surfactant/H2O/decanol) mesomorphism at room temp. are reported. The phase behavior of the ternary system was studied and both hexagonal and lamellar phases were identified.the investigated ligand systems are based on a tetra-anionic diamidate-diphenolate ligand which forms dianionic oxovanadium complexes with high stability in aq. environments. [on SciFinder(R)] -
1995
Controlling Intermolecular Interactions between Metallomesogens: Side-Chain Effects in Discotic Copper, Palladium, and Vanadyl Bis($beta$-Diketonates).
Chemistry of Materials,vol.7,p.2067–2077,1995A systematic study of the liq.-cryst. properties of 30 metal bis($beta$-diketonate) complexes (M = Cu, VO, Pd) that exhibit discotic mesophases is reported. This study has detd. that the ability of the metal center to influence the mesophase stability depends upon the d. of side chains. In the 10-side-chain complexes I, all of the materials were liq. cryst. In this series the M = VO analogs have lower melting and clearing points than those with M = Cu and M = Pd. For the 12-side-chain series II the opposite is true, and the M = VO materials have substantially higher clearing points. The differences between series I and II arise from the enhanced core-core interactions that accompany the increased side-chain d. The side-chain-induced organization assists the expression of the metal center’s character in detg. the stability and nature of the mesophase. The fact that the transition temps. of the M = Cu and M = Pd compds. differ more in series II than in series I is also a manifestation of this greater organization. The influence of the metal centers is discussed in the context of intermol. dative assocns. and for some phases of the M = VO materials these interactions produce polymeric (-V:O-V:O-)n structures. [on SciFinder(R)]
