Showing papers by "Tobin J. Marks published in 2003"

Easily processable phenylene-thiophene-based organic field-effect transistors and solution-fabricated nonvolatile transistor memory elements.

Abstract: The synthesis of a new series of mixed phenylene−thiophene oligomers is reported; 2,5-bis(4-n-hexylphenyl)thiophene (dH-PTP, 1), 5,5‘-bis(4-n-hexylphenyl)-2,2‘-bithiophene (dH-PTTP, 2), 5,5‘ ‘-bis(4-n-hexylphenyl)-2,2‘:5‘,2‘ ‘-terthiophene (dH-PT3P, 3), 5,5‘ ‘‘-bis(4-n-hexylphenyl)-2,2‘:5‘,2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (dH-PT4P, 4), 1,4-bis[5-(4-n-hexylphenyl)-2-thienyl]benzene (dH-PTPTP, 5), and 2,5-bis[4(4‘-n-hexylphenyl)phenyl]thiophene (dH-PPTPP, 6) were characterized by 1H NMR, elemental analysis, UV−visible spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Vacuum-evaporated and solution-cast films were characterized by X-ray diffraction and scanning electron microscopy. All compounds display high p-type carrier mobilities as evaporated (up to 0.09 cm2/Vs) and as solution-cast (up to 0.03 cm2/Vs) films on both Si/SiO2 and ITO/GR (glass resin) substrates. The straightforwardly synthesized dH-PTTP (2) displays an unprecedented combination of mobility, on/off ratio, stab...

C2-Symmetric Bis(oxazolinato)lanthanide Catalysts for Enantioselective Intramolecular Hydroamination/Cyclization

Abstract: C2-symmetric bis(oxazolinato)lanthanide complexes of the type [(4R,5S)-Ph2Box]La[N(TMS)2]2, [(4S,5R)-Ar2Box]La[N(TMS)2]2, and [(4S)-Ph-5,5-Me2Box]La[N(TMS)2]2 (Box = 2,2‘-bis(2-oxazoline)methylenyl; Ar = 4-tert-butylphenyl, 1-naphthyl; TMS = SiMe3) serve as precatalysts for the efficient enantioselective intramolecular hydroamination/cyclization of aminoalkenes and aminodienes. These new catalyst systems are conveniently generated in situ from the known metal precursors Ln[N(TMS)2]3 or Ln[CH(TMS)2]3 (Ln = La, Nd, Sm, Y, Lu) and 1.2 equiv of commercially available or readily prepared bis(oxazoline) ligands such as (4R,5S)-Ph2BoxH, (4S,5R)-Ar2BoxH, and (4S)-Ph-5,5-Me2BoxH. The X-ray crystal structure of [(4S)-tBuBox]Lu[CH(TMS)2]2 provides insight into the structure of the in situ generated precatalyst species. Lanthanides having the largest ionic radii exhibit the highest turnover frequencies as well as enantioselectivities. Reaction rates maximize near 1:1 BoxH:Ln ratio (ligand acceleration); however, incr...

Organolathanide-catalyzed regioselective intermolecular hydroamination of alkenes, alkynes, vinylarenes, di- and trivinylarenes, and methylenecyclopropanes. Scope and mechanistic comparison to intramolecular cyclohydroaminations.

Abstract: Organolanthanide complexes of the type Cp'(2)LnCH(SiMe(3))(2) (Cp' = eta(5)-Me(5)C(5); Ln = La, Nd, Sm, Lu) and Me(2)SiCp' '(2)LnCH(SiMe(3))(2) (Cp' ' = eta(5)-Me(4)C(5); Ln = Nd, Sm, Lu) serve as efficient precatalysts for the regioselective intermolecular hydroamination of alkynes R'Ctbd1;CMe (R' = SiMe(3), C(6)H(5), Me), alkenes RCH=CH(2) (R = SiMe(3), CH(3)CH(2)CH(2)), butadiene, vinylarenes ArCH=CH(2) (Ar = phenyl, 4-methylbenzene, naphthyl, 4-fluorobenzene, 4-(trifluoromethyl)benzene, 4-methoxybenzene, 4-(dimethylamino)benzene, 4-(methylthio)benzene), di- and trivinylarenes, and methylenecyclopropanes with primary amines R' 'NH(2) (R' ' = n-propyl, n-butyl, isobutyl, phenyl, 4-methylphenyl, 4-(dimethylamino)phenyl) to yield the corresponding amines and imines For R = SiMe(3), R = CH(2)=CH lanthanide-mediated intermolecular hydroamination regioselectively generates the anti-Markovnikov addition products (Me(3)SiCH(2)CH(2)NHR' ', (E)-CH(3)CH=CHCH(2)NHR' ') However, for R = CH(3)CH(2)CH(2), the Markovnikov addition product is observed (CH(3)CH(2)CH(2)CHNHR' 'CH(3)) For internal alkynes, it appears that these regioselective transformations occur under significant stereoelectronic control, and for R' = SiMe(3), rearrangement of the product enamines occurs via tautomerization to imines, followed by a 1,3-trimethylsilyl group shift to stable N-SiMe(3)-bonded CH(2)=CMeN(SiMe(3))R' ' structures For vinylarenes, intermolecular hydroamination with n-propylamine affords the anti-Markovnikov addition product beta-phenylethylamine In addition, hydroamination of divinylarenes provides a concise synthesis of tetrahydroisoquinoline structures via coupled intermolecular hydroamination/subsequent intramolecular cyclohydroamination sequences Intermolecular hydroamination of methylenecyclopropane proceeds via highly regioselective exo-methylene C=C insertion into Ln-N bonds, followed by regioselective cyclopropane ring opening to afford the corresponding imine For the Me(2)SiCp' '(2)Nd-catalyzed reaction of Me(3)SiCtbd1;CMe and H(2)NCH(2)CH(2)CH(2)CH(3), DeltaH() = 172 (11) kcal mol(-)(1) and DeltaS() = -259 (97) eu, while the reaction kinetics are zero-order in [amine] and first-order in both [catalyst] and [alkyne] For the same substrate pair, catalytic turnover frequencies under identical conditions decrease in the order Me(2)SiCp' '(2)NdCH(SiMe(3))(2) > Me(2)SiCp' '(2)SmCH(SiMe(3))(2) > Me(2)SiCp' '(2)LuCH(SiMe(3))(2) > Cp'(2)SmCH(SiMe(3))(2), in accord with documented steric requirements for the insertion of olefinic functionalities into lanthanide-alkyl and -heteroatom sigma-bonds Kinetic and mechanistic evidence argues that the turnover-limiting step is intermolecular C=C/Ctbd1;C bond insertion into the Ln-N bond followed by rapid protonolysis of the resulting Ln-C bond

Intramolecular Hydroamination/Cyclization of Conjugated Aminodienes Catalyzed by Organolanthanide Complexes. Scope, Diastereo- and Enantioselectivity, and Reaction Mechanism

Abstract: Organolanthanide complexes of the general type Cp'(2)LnCH(TMS)(2) (Cp' = eta(5)-Me(5)C(5); Ln = La, Sm, Y; TMS = SiMe(3)) and CGCSmN(TMS)(2) (CGC = Me(2)Si(eta(5)-Me(4)C(5))((t)()BuN)) serve as effective precatalysts for the rapid, regioselective, and highly diastereoselective intramolecular hydroamination/cyclization of primary and secondary amines tethered to conjugated dienes. The rates of aminodiene cyclizations are significantly more rapid than those of the corresponding aminoalkenes. This dienyl group rate enhancement as well as substituent group (R) effects on turnover frequencies is consistent with proposed transition state electronic demands. Kinetic and mechanistic data parallel monosubstituted aminoalkene hydroamination/cyclization, with turnover-limiting C=C insertion into the Ln-N bond to presumably form an Ln-eta(3) allyl intermediate, followed by rapid protonolysis of the resulting Ln-C linkage. The rate law is first-order in [catalyst] and zero-order in [aminodiene]. However, depending on the particular substrate and catalyst combination, deviations from zero-order kinetic behavior reflect competitive product inhibition or self-inhibition by substrate. Lanthanide ionic radius effects and ancillary ligation effects on turnover frequencies suggest a sterically more demanding Ln-N insertion step than in aminoalkene cyclohydroamination, while a substantially more negative DeltaS( double dagger ) implies a more highly organized transition state. Good to excellent diastereoselectivity is obtained in the synthesis of 2,5-trans-disubstituted pyrrolidines (80% de) and 2,6-cis-disubstituted piperidines (99% de). Formation of 2-(prop-1-enyl)piperidine using the chiral C(1)-symmetric precatalyst (S)-Me(2)Si(OHF)(CpR)SmN(TMS)(2) (OHF = eta(5)-octahydrofluorenyl; Cp = eta(5)-C(5)H(3); R = (-)-menthyl) proceeds with up to 71% ee. The highly stereoselective feature of aminodiene cyclization is demonstrated by concise syntheses of naturally occurring alkaloids, (+/-)-pinidine and (+)-coniine from simple diene precursors.

Layer-by-Layer Self-Assembled Pyrrole-Based Donor-Acceptor Chromophores as Electro-Optic Materials

Abstract: The synthesis of the heterocycle-based diethanolaminomethyl-functionalized derivative 1-(pyridin-4-yl)-2-[(N-methylpyrrol-2-yl)-5-methylenediethanolamine]ethene (2) from (1-pyridin-4-yl)-2-(N-methy...

Electronic structure of conducting polymers: Limitations of oligomer extrapolation approximations and effects of heteroatoms

Abstract: Density-functional methods are used to analyze the scaling of discrete oligomeric π-electron conducting molecules towards idealized isolated polymer chains, treated in periodic boundary conditions. The band gaps of a series of conjugated oligomers of incrementally increasing lengths exactly fit a nearly-free-electron molecular-orbital picture and exhibit a smooth deviation from the classical empirical "I/N" trend for long oligomers and infinite polymers. The calculations also show a smooth convergence of bond lengths. The full band structures and densities of states of a polyacetylene, polypyrrole, polyfuran, and polythiophene show that band crossing, localized bands, and other effects cannot be accurately determined from simple extrapolation of oligomer electronic structures. Systematic comparisons of the electronic structure variations of the polymers investigated indicate that the electron affinity, rather than the electronegativity of the heteroatom or the bond-length alternation of the conjugated backbone, significantly affects the band gap of the resulting polymer as indicated by the presence of heteroatom states in the partial density of states of the conduction band, requiring revision of previous semiempirical analyses. Consequences for doping processes are also studied, along with a comparison of valence bandwidths, conduction bandwidths, and carrier effective masses as a function of heteroatom.

Organic Light-Emitting Diodes and Methods for Assembly and Enhanced Charge Injection

Abstract: New organic light-emitting diodes and related electroluminescent devices and methods for fabrication, using siloxane self-assembly techniques.

Synthesis, Spectroscopy, and Catalytic Properties of Cationic Organozirconium Adsorbates on “Super Acidic” Sulfated Alumina. “Single-Site” Heterogeneous Catalysts with Virtually 100 Active Sites

Abstract: Sulfated alumina (AlS), a highly Bronsted acidic sulfated metal oxide, is prepared by the impregnation of γ-alumina with 1.6 M H2SO4, followed by calcination at 550 °C for 3 h. 13C CPMAS NMR spectroscopy of the chemisorbed 13Cα-enriched organozirconium hydrocarbyl Cp‘2Zr(13CH3)2 (2*)/AlS (Cp‘ = η5-(CH3)5C5) reveals that the chemisorption process involves M−C σ-bond protonolysis at the strong surface Bronsted acid surface sites to yield a “cation-like” highly reactive zirconocenium electrophile, Cp‘2Zr13CH3+. In contrast, chemisorption of 2* on dehydroxylated alumina (DA) yields a similar cation via methide transfer to surface Lewis acid sites, while chemisorption onto dehydroxylated silica yields a μ-oxo Cp‘2Zr(13CH3)−OSi⋮ species. Two complementary active site kinetic assays for benzene hydrogenation show that, unlike typical heterogeneous and supported organometallic catalysts, 97 ± 2% of all Cp‘ZrMe3 (3)/AlS sites are catalytically significant, demonstrating that the species identified by 13C CPMAS NMR...

Hot microcontact printing for patterning ITO surfaces. Methodology, morphology, microstructure, and OLED charge injection barrier imaging

Abstract: A soft lithographic microcontact printing (μCP) procedure is successfully applied for the first time to form densely packed organosilane self-assembled monolayers (SAMs) on the surface of ITO (Sn-doped In2O3) coated glass via a thermally activated deposition process. Hot microcontact printing (HμCP) enables localized transfer with 1.0−40 μm feature sizes of dense docosyltrichlorosilane (CH3(CH2)20CH2SiCl3 = DTS) monolayer patterns onto ITO, which reacts sluggishly under conventional μCP conditions. X-ray reflectivity measurements yield a thickness of 12.1 ± 0.1 A and a surface roughness of 2.8 ± 0.1 A for HμCP printed DTS films, which is well within the range for self-assembled monolayer formation, while the weak reflected intensity from conventionally prepared DTS films indicates a poorly organized monolayer structure. Noncontact mode AFM studies reveal that HμCP creates uniform SAMs over a wide area with excellent line edge resolution, while the original patterns are poorly transferred by conventional μ...

Molecularly "engineered" anode adsorbates for probing OLED interfacial structure-charge injection/luminance relationships: large, structure-dependent effects.

Abstract: Molecule-scale structure effects at organic light-emitting diodes (OLED) anode−organic transport layer interfaces are probed via a self-assembly approach. A series of ITO anode-linked silyltriarylamine molecules differing in aryl group and linker density are synthesized for this purpose and used to probe the relationship between nanoscale interfacial chemical structure, charge injection and electroluminescence properties. Dramatic variations in hole injection magnitude and OLED performance can be correlated with the molecular structures and electrochemically derived heterogeneous electron-transfer rates of such triarylamine fragments, placed precisely at the anode−hole transport layer interface. Very bright and efficient (∼70 000 cd/m2 and ∼2.5% forward external quantum efficiency) OLEDs have thereby been fabricated.

Metallocene polymerization catalyst ion-pair aggregation by cryoscopy and pulsed field gradient spin-echo NMR diffusion measurements.

Abstract: Pulsed field gradient spin−echo (PGSE) NMR and cryoscopic measurements have been performed on a series of homogeneous metallocene polymerization catalyst ion-pairs to determine if aggregation is a significant phenomenon under typical polymerization conditions. Cryoscopic measurements on [(Me5Cp)2ZrMe]+[MeB(C6F5)3]- (1), [rac-Et(Indenyl)2ZrMe]+[MeB(C6F5)3]- (2), [(1,2-Me2Cp)2ZrCHTMS2]+[MeB(C6F5)3]- (3), [Me2Si(Me4Cp)(t-BuN)TiMe]+[MeB(C6F5)3]- (4), [Me2Si(Me4Cp)(t-BuN)ZrMe]+[MeB(C6F5)3]- (5), and [Me2C(Fluorenyl)(Cp)ZrMe]+[MeB(C6F5)3]- (6) were carried out in benzene in the 10−18 millimolal concentration range. PGSE measurements, using (p-tolyl)4Si as an internal standard, were also performed on catalyst ion-pairs 1, 4, 6, [(Me5Cp)2ThMe]+[B(C6F5)4]- (7), [(Me2SiCp2)ZrMe]+[MeB(C6F5)3]- (8), and [Cp2ZrMe]+[MeB(C6F5)3]- (9) in the 0.8−10.0 millimolar range. All results are consistent with a 1:1 ion-pair structural model and show little evidence for ion-quadruples or higher-order aggregates.

Realization of high-efficiency/high-luminance small-molecule organic light-emitting diodes: synergistic effects of siloxane anode functionalization/hole-injection layers, and hole/exciton-blocking/electron-transport layers

Abstract: High-efficiency/high-luminance small-molecule organic light-emitting diodes (OLEDs) are fabricated by combining thin, covalently-bound triarylamine hole injection/adhesion interlayers with hole- and exciton-blocking/electron transport interlayers in tris(8-hydroxyquinolato)aluminum (III) (Alq)-based OLEDs. Power and forward external quantum efficiencies as high as 15.2 lm/W and 4.4±0.5%, respectively, and turn-on voltages ∼4.5 V are achieved in devices of the structure ITO/TPDSi2/NPB/Alq:DIQA/BCP/Li/MgAg [NPB=(N,N′-di(1-napthl)-N,N′-diphenyl benzidine)] TPDSi2 interlayers are straightforwardly fabricated by spin-casting N,N′-diphenyl-N,N′- bis(p-trichlorosilylpropylphenyl)(1,1′-biphenyl)-4,4′-diamine TPDSi2 onto the ITO surface, while 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) interlayers are introduced by thermal evaporation. High quantum efficiencies are attributed to the synergistic enhanced hole/electron injection and exciton confinement effects of the TPDSi2 and BCP interlayers, respectively.

Vapor phase self-assembly of electrooptic thin films via triple hydrogen bonds

Abstract: The donor−acceptor π-electron chromophore 5-{4-[2-(4,6-diamino-[1,3,5]triazin-2-yl)-vinyl]-benzylidene}-pyrimidine-2,4,6-trione (DTPT) was designed and synthesized. Triple H-bonding interactions between neighboring molecules direct self-assembled chromophore alignment in a head-to-tail orientation using a straightforward vapor phase deposition process. Angle-dependent SHG interference patterns and the quadratic dependence of the 532 nm light output intensity on the thickness of the DTPT films for glass substrates coated on both sides demonstrate high, reproducible film quality and uniformity. XRD also demonstrates long-range order in the film and yields a molecular tilt angle in good agreement with polarized SHG data, clearly showing that out-of-plane ordering of chromophore molecules has been achieved.

Twisted π-system electro-optic chromophores. A CIS vs. MRD-CI theoretical investigation

Abstract: Twisted, merocyanine-type molecules are investigated theoretically as chromophores, whose optical and electro-optic responses can be controlled via steric repulsion-mediated tuning of the central dihedral angle. Employing multi-reference determinant computational methods results in significant modifications to the quantitative aspects of the response properties, compared to values computed using a single determinant ground state, and leads to computed hyperpolarizabilities even larger than previously estimated. Using either computational approach demonstrates that fine control of the sharp variations in response properties can be achieved by using substituent-induced steric repulsions to modify the internal dihedral twist angles.

Organotitanium-mediated stereoselective coordinative/insertive homopolymerizations and copolymerizations of styrene and methyl methacrylate.

Abstract: This contribution describes coordinative/insertive stereoregular homopolymerizations and copolymerizations of styrene and methyl methacrylate (MMA) mediated by a highly active single-site organotitanium catalyst. The catalyst system used to effect these polymerizations of nonpolar and polar olefinic monomers is prepared by in situ Zn reduction of the precursor derived from the reaction (Me5Cp)TiMe3 + Ph3C+B(C6F5)4-. The resulting catalyst produces polystyrene (>95% syndiotactic, 170 000 g/mol molecular weight; s-PS) by the established coordinative/insertive pathway. The same catalyst mediates polymerization of MMA to poly(methyl methacrylate) (>65% syndiotactic, >70 000 g/mol molecular weight; s-PMMA) by a group transfer protocol-like (GTP-like) pathway (1,4 insertion mechanism). Under optimal conditions, this catalyst also mediates the copolymerization of MMA + styrene (1:19 ratio) at 50 °C to yield random ∼80% coisotactic poly[styrene-co-(methyl methacrylate)] (coiso-PSMMA) which contains ∼4% MMA. Contr...

Interrupted-Growth Studies of the Self-Assembly of Intrinsically Acentric Siloxane-Derived Monolayers

Abstract: The evolution of an intrinsically acentric monolayer formed by self-assembly of a trimethoxysilane-functionalized, high-β azobenzene-based chromophore from solution onto hydrophilic silicon oxide s...

Second-generation approach to all-organic modulators based on intrinsically polar self-assembled molecular superlattices

Abstract: T. J. MarksNorthwestern UniversityDepartment of ChemistryandMaterials Research CenterEvanston, Illinois 60208-3113Abstract. Intrinsically acentric self-assembled superlattices(SASs) have been directly grown in a layer-by-layer processon the commercially available polymer Cyclotene™. Usingthe high-temperature/high-transparency fluoropolyether Cy-top™ as a cladding layer, the SAS films have been used tosuccessfully fabricate traveling-wave electro-optic (EO)modulators, demonstrating a straightforward approach to-ward ‘‘all-organic’’ modulators.

Improved Transparent Conducting Oxides for Photovoltaics: Final Research Report, 1 May 1999--31 December 2002

Abstract: This subcontract focused on next-generation transparent conducting oxides (TCOs) for improved PV performance. More specifically, there were two research foci: (1) improved Sn-based, n-type TCOs aimed at enhanced CdTe PV cell performance, and (2) novel Cu-based, p-type TCOs applicable to a variety of PV designs. The objective of the research under this subcontract was to identify, explore, evaluate, and develop future generations of photovoltaic technologies that can meet the long-term goal of producing low-cost electricity from sunlight.

Electro-optic waveguide modulators by the integration of self-assembled superlattices with polymeric and semiconductor materials

Abstract: We describe here the fabrication and characterization of novel organic electro-optic materials composed of self-assembled superlattices. The SAS structures are intrinsically acentric and exhibit large second harmonic generation and electro-optic responses. This approach using SAS electro-optic materials has advantages such as not requiring poling for creating nonlinearity in the films and efficient film growth on a variety of substrates over large areas. Prototype waveguide electro-optic modulators have been fabricated using SAS films integrated wtih low-loss polymeric materials functioning as partial guiding and cladding layers. The waveguide EO modulators are fabricated using a multistep process including e-beam deposition, plasma-enhanced chemical vapor deposition, photolithogrpahy, and reactive ion etching. Electro-optic parameters such as thehalf-wave voltage and the effective electro-optic coefficient, and the velocity mismatch between the optical and radio frequency waves have been evaluated.

Nanoprecise Self-Assembly of Electro-Optic and Electroluminescent Molecular Arrays

Abstract: Although the current state of molecular synthesis has reached an impressive level of sophistication in the past decades, the ability of scientists to organize array of engineered molecular building blocks to achieve certain specific materials functions is currently in its infancy. Of particular attraction would be pathways which led via spontaneous self-organization processes to robust arrays of molecules with designed electronic and/or opto-electronic characteristics and spatial relationships. Ideally, the structural control of the assembly process would be at the sub-nm level and the structures would “click” into place after initial self-assembly. In the present contribution, we briefly discuss two complementary efforts to achieve such capabilities. In one effort, we focus on self-assembly routes to fabricate nanoscopically acentric arrays of high-hyperpolarizability building blocks for electro-optic function and in the other on the nanoscopic interfacial phenomena that tune charge injection and radiative recombination efficiencies in electroluminescent molecule-based organic heterostructures. Each approach makes use of well-characterized siloxane condensation chemistry, which can be used in successions of self-limiting chemisorptive processes, to deposit conformai, adherent, and virtually pin hole-free layers of molecular entities with sub-nm precision. An important consideration here is to apply a battery of physical characterization techniques to precisely define nanostructure and to correlate this with photonic response.

N- and P-Type Building Blocks for Organic Electronics Based on Oligothiophene Cores

Abstract: Organic semiconductors exhibiting complementary-type carrier mobility are the key components for the development of the field of “gplastic electronics” We present here a novel series of α,ω- and isomerically pure ββ’-diperfluorohexyl-substituted thiophene and study the impact of fluoroalkyl substitution and conjugation length vis-a-vis the corresponding fluorinefree analogues. Trends between the fluorinated and fluorine-free families in molecular packing, HOMO-LUMO gap, and π-π interactions are found to be strikingly similar. TFT measurements indicate that all members of the fluorinated series are n-type semiconductors

Materials for n-type organic electronics: synthesis and properties of fluoroarene-thiophene semiconductors

Abstract: Recent progress in the field of organic electronics is due to a fruitful combination of both innovative molecular design and promising low-cost material/device assembly. Targeting the first strategy, we present here the general synthesis of fluoroarene-containing thiophene-based semiconductors and the study of their properties with respect to the corresponding fluorine-free hole-transporting analogues. The new compounds have been characterized by elemental analysis, mass spectrometry, and 1H- and 19F NMR. The dramatic influence of fluorine substitution and molecular architecture has been investigated by solution/film optical absorption, fluorescence emission, and cyclic voltammetry. Single crystal data for all of the oligomers have been obtained and will be presented. Film microstructure and morphology of this new class of materials have been studied by XRD and SEM. Particular emphasis will be posed on the solution-processable oligomers and polymers.