A series of novel diketopyrrolopyrrole (DPP)-containing polyfluorenes, coded as PF-DPP01-50, were synthesized through palladium-catalyzed Suzuki polycondensation with different feed ratios between fluorene dibromide and DPP dibromide. Their chemical structures and compositions were verified by 1H NMR and elemental analysis. DSC and TGA results show that they have good to excellent thermal stabilities. Absorption and photoluminescence (PL) properties of PF-DPP01-50, determined in both CHCl3 solutions and thin films, exhibit regular changes with increasing of DPP contents in copolymers, with absolute PL efficiencies being in the range 13.8-26.9%. Electroluminescence (EL) properties of all the copolymers were investigated with device configurations of ITO/PEDOT/copolymer/Ba/Al and ITO/PEDOT/copolymer/Al. A very low content of DPP units (1%) is needed to achieve full energy transfer from fluorene segments to DPP units; hence, exclusive emission of the latter occurs. EL colors of these copolymers vary from orange to red, corresponding to CIE coordinates from (0.52, 0.46) to (0.62, 0.37). The best performance was achieved by orange-emitting PF-DPP01 in device configuration of ITO/PEDOT/copolymer/Ba/Al, with maximum EQE of 0.45% and maximum brightness of 520 cd/m2. Devices with configuration of ITO/PEDOT/copolymer/Al prove that DPP units can effectively improve the electron affinity of these copolymers. One of these devices (ITO/PEDOT/PF-DPP25/Al) can realize maximum EQE of 0.14% and maximum brightness of 127 cd/m2. Therefore, color-tuning (red-shift) and improvement of electron affinity can be achieved at the same time through incorporation of DPP units.
Macromolecules, 39 (24 ), 8347 -8355 , 2006 .
Wednesday, July 16, 2008
Monday, June 23, 2008
Saturday, June 21, 2008
Synthesis and Properties of Novel Low-Band-Gap Thienopyrazine-Based Poly(heteroarylenevinylene)s
]pyrazine-based poly(heteroarylenevinylene)s (PHAVs) (P-1-P-6) by Horner polycondensation and cyano-PHAVs (P-7-P-9) by Knoevenagel polycondensation have been synthesized in quantitative yields. The copolymers are characterized by NMR, IR, UV, GPC, and elemental analysis. High molecular weight (
w up to 279 000 g/mol), thermostable, soluble, and film-forming materials were obtained. The absorption spectra of the polymers show two peaks located in the UV and visible region from ~384 to 650 nm and are promising for the application in polymer solar cells. The absorption and emission in solution and in solid state of the polymers revealed that the polymers generate a 
-stacked structure in the solid state, and the polymer molecules in the film were ordered. Thin films of the polymers P-1-P-9 exhibit an optical band gap of ~1.56-2.08 eV. Cyclic voltammograms display that the p-doping/dedoping and n-doping/dedoping processes of the polymers (P-1, P-2, P-3, P-5, and P-6) are reversible. The HOMO and LUMO levels of the polymers were determined from electrochemical measurements. From the absorption spectra of the polymers (P-1, P-2, and P-8) in chloroform/methanol mixtures, all the three polymers have revealed solvatochromic effects, which have been related to the formation of aggregates.
Macromolecules, 39 (23 ), 7844 -7853 , 2006
w up to 279 000 g/mol), thermostable, soluble, and film-forming materials were obtained. The absorption spectra of the polymers show two peaks located in the UV and visible region from ~384 to 650 nm and are promising for the application in polymer solar cells. The absorption and emission in solution and in solid state of the polymers revealed that the polymers generate a -stacked structure in the solid state, and the polymer molecules in the film were ordered. Thin films of the polymers P-1-P-9 exhibit an optical band gap of ~1.56-2.08 eV. Cyclic voltammograms display that the p-doping/dedoping and n-doping/dedoping processes of the polymers (P-1, P-2, P-3, P-5, and P-6) are reversible. The HOMO and LUMO levels of the polymers were determined from electrochemical measurements. From the absorption spectra of the polymers (P-1, P-2, and P-8) in chloroform/methanol mixtures, all the three polymers have revealed solvatochromic effects, which have been related to the formation of aggregates.Star-Shaped Oligofluorenes End-Capped with Carboxylic Groups: Syntheses and Self-Assembly at the Liquid–Solid Interface
A series of star-shaped oligofluorenes end-capped with carboxylic acid groups were synthesized. Different numbers of carboxyl groups that can form hydrogen bonds, and long alkane chains that have stabilizing effects, were intentionally introduced. The resulting molecular architectures of the so-prepared star-shaped oligofluorenes at the liquid–solid interface were investigated by scanning tunneling microscopy. It is found that the number of hydrogen-bonding groups and the symmetry of the target molecules have crucial influences on the structures of the ordered assemblies.
Wednesday, June 18, 2008
Facile Horner-Emmons Synthesis of Defect-Free Poly(9,9-dialkylfluorenyl-2,7-vinylene)
This paper describes a simple new strategy for preparing poly(9,9-dialkylfluorenyl-2,7-vinylenes) (PFVs) having high molecular weights and no detectable saturated defects along the conjugated backbone. The new route utilizes a modified Horner-Emmons method by coupling suitably designed comonomers to form the targeted conjugated polymers. The newly prepared PFVs were directly compared to PFVs prepared via a previously established Gilch polymerization route. The structure and optical properties of all PFVs were characterized by gel permeation chromatography (GPC), NMR spectroscopy, UV-vis, fluorescence, and photoluminescence spectroscopy. The findings indicate that the modified Horner-Emmons route gave PFVs with lower molecular weights but substantially higher yields and fewer defects than those prepared by using the Gilch route.
Macromolecules, 39 (10 ), 3494 -3499 , 2006 .
Monday, May 5, 2008
Combined Spectroelectrochemical and Theoretical Study of a Vinylene-Bridged Sexithiophene Cooligomer: Analysis of the -Electron Delocalization
The electronic and the Fourier transform Raman (FT-Raman) spectra of a novel well-barrier-well vinylene-bridged sexithiophene in neutral and in doped states have been recorded. The samples were oxidized chemically, with trifluoroacetic acid or ferric chloride, and electrochemically in dichloromethane solutions. The evolution of the Raman spectral pattern upon oxidation at different anodic potentials has been analyzed for a thin solid film of the material. Experimental observations are explained by the initial generation of a radical cation species followed by the generation of a dication species. A comprehensive assignment of the electronic and Raman spectroscopic features observed in both neutral and oxidized states has been performed on the basis of density functional theory (DFT) calculations. Time-dependent DFT calculations have been performed to calculate the electronic excitation energies. The experimental data and theoretical results give a clear picture of the structure and electronic properties of the charge defects created on this vinylene-bridged sexithiophene.
J. Phys. Chem. B, 106 (15 ), 3872 -3881 , 2002
Thursday, April 24, 2008
Saturday, April 5, 2008
Synthesis and Characterization of the Electronic and Electrochemical Properties of Thienylenevinylene Oligomers with Multinanometer Dimensions
Soluble thienylenevinylene oligomers based on 3,4-dihexylthiophene with chain length approaching 100 Å (16-mer) have been synthesized. Optical data obtained in solution and on solution-processed thin films show that chain extension produces a narrowing of the HOMO-LUMO gap (
E) and band gap (Eg) which reach values significantly smaller than that of the parent polymer. Plots of E and Eg vs the reciprocal number of carbons in the chain (1/Cn) reveal a deviation from linearity beyond the 10-12-mer suggesting a limit of convergence around the 20-22-mer. Cyclic voltammetry shows that chain lengthening induces a negative shift of the first redox potential, an increase of the number of accessible redox states, and a decrease of the Coulombic repulsion in multicationic species. Thus, the 16-mer can be charged up to the hexacationic state within a 0.60-V potential window. A plot of the potential of the various redox steps vs 1/Cn suggests full coalescence into a single-step process for the 20-22-mer. A single process is indeed observed for solution cast films of 16-mer, and the respective contributions of the intra- and intermolecular mechanisms in the recombination process are discussed.
J. Am. Chem. Soc., 120 (32 ), 8150 -8158 , 1998 .
E) and band gap (Eg) which reach values significantly smaller than that of the parent polymer. Plots of E and Eg vs the reciprocal number of carbons in the chain (1/Cn) reveal a deviation from linearity beyond the 10-12-mer suggesting a limit of convergence around the 20-22-mer. Cyclic voltammetry shows that chain lengthening induces a negative shift of the first redox potential, an increase of the number of accessible redox states, and a decrease of the Coulombic repulsion in multicationic species. Thus, the 16-mer can be charged up to the hexacationic state within a 0.60-V potential window. A plot of the potential of the various redox steps vs 1/Cn suggests full coalescence into a single-step process for the 20-22-mer. A single process is indeed observed for solution cast films of 16-mer, and the respective contributions of the intra- and intermolecular mechanisms in the recombination process are discussed.Absorption Properties of Alkoxy-Substituted Thienylene-Vinylene Oligomers as a Function of the Doping Level
In an attempt to improve on the properties of PEDOT (poly(3,4-ethylenedioxythiophene)) as a stable, conducting, and transparent coating we synthesized four different alkoxy-substituted poly(thienylene-vinylene)s, 1-4, using the Stille coupling reaction. The oligomers and polymers obtained were characterized and their NIR-vis absorption spectra were measured as a function of doping, both electrochemically as films and chemically in solution. Similar spectra of PEDOT films were gathered for comparison. In PEDOT a change in doping level does not change the energies of the absorption bands, while for the other polymers the bands shift markedly and the NIR peak at high doping level lies at a higher energy. The polymers 1-4 are much less suited for the intended coatings than PEDOT. Possible reasons for this are discussed.
Friday, April 4, 2008
Thursday, April 3, 2008
Synthesis, Spectral Stability, and Electroluminescent Properties of Random Poly(2,7-fluorenylenevinylene-co-3,6-carbazolylenevinylene) Obtained by a S
The synthesis of a series of new random poly(9,9-dioctyl-2,7-fluorenylenevinylene-co-N-octyl-3,6-carbazolylenevinylene) copolymers at 20-80% mol/mol of carbazole (P2-P6) was achieved by a versatile Suzuki-Heck reaction cascade between the suitable dibromoaryl derivatives at different monomer ratios and potassium vinyltrifluoroborate. Their properties have been investigated by 1H NMR, IR, TGA, DSC, cyclic voltammetry, UV-vis, and photoluminescence and compared to those of poly(9,9-dioctyl-2,7-fluorenylenevinylene) (P1) obtained by the same method. The control of the
-conjugation extension and the inductive effects, determined by the amount of carbazolyl-3,6-ene moieties, permitted the modulation of the HOMO and LUMO energy levels of these materials without remarkably modifying their emission properties. Furthermore, different from poly(9,9-dioctylfluorene), a good spectral stability in the solid state was proven for P1 after a thermal annealing under air at 130 
C. The electroluminescence properties of the materials were tested by constructing OLED devices of ITO/PEDOT-PSS/P1-P6/Ca/Al configuration. The improvement of the device performances for P2-P4 (20-50 mol/mol of carbazole) with respect to P1 was attributed to the better hole transport in the material because of the presence of carbazole units. The better performances of P5 (450 cd/m2 at 22 V, 0.0225 cd/A at 22 V) were ascribed to the easier injection of electrons in the device with respect to the other copolymers, as a consequence of its higher electron affinity. These figures of merit could be improved by inserting a suitable electron injecting layer (Alq3) between the cathode and P5 (890 cd/m2 at 18 V, 0.0435 cd/A at 10 V).Sunday, March 30, 2008
Synthesis of Poly(arylenevinylene)s with Fluorinated Vinylene Units
Poly(arylenevinylene) polymers bearing fluorine atoms in the vinylene units were obtained by a Stille cross-coupling reaction of (E)-(1,2-difluoro-1,2-ethenediyl)bis(tributylstannane) with diiodoaryl derivatives. The introduction of fluorine atoms on the double bond of the stannane leads to polymers with relatively high molecular weights. Furthermore, the presence of fluorinated vinylene units changes the optical properties of the polymers and shifts the emission towards the blue region of the visible spectrum. A fluorinated analogue of MEH-PPV was obtained, and it shows photoluminescence that is considerably blueshifted, also in the solid state, relative to that found for nonfluorinated MEH-PPV and to other PPVs with fluorinated double bonds.
European Journal of Organic Chemistry DOI: 10.1002/ejoc.200700815
Wednesday, March 26, 2008
Catalytic Hunsdiecker Reaction and One-Pot Catalytic Hunsdiecker–Heck Strategy: Synthesis of α,β-Unsaturated Aromatic Halides, α-(Dihalomethyl)benzene
The reaction of α,β-unsaturated aromatic (or heteroaromatic) carboxylic acids with N-halosuccinimides (1 equiv.) and catalytic tetrabutylammonium trifluoroacetate (0.2 equiv.) in dichloroethane results in facile halodecarboxylation affording the corresponding (E)-halides in good to excellent yields. A similar reaction, but with 2 equiv. of N-halosuccinimides in acetonitrile-water (1:1 v/v) results in the exclusive formation of the corresponding α-(dihalomethyl)benzenemethanols. Furthermore, a one-pot strategy has been developed combining catalytic Hunsdiecker reaction (using tetrabutylammonium trifluoroacetate in dichloroethane) and Heck coupling (using palladium acetate/triethylamine/triphenylantimony/dichloroethane) for the synthesis of 5-aryl-2,4-pentadienoic acids, esters and amides in moderate to good yields. The natural product piperine and pipergualamine has been synthesized via the above route. Mechanistic and theoretical studies (via AM1 calculations) provide a useful insight into the mechanism of the present halodecarboxylation reaction, suggesting an ionic pathway involving the attack of the halogenium ion across the carbon–carbon double bond, triggering the elimination of carbon dioxide.
Tetrahedron
doi:10.1016/S0040-4020(99)01035-2 Saturday, March 22, 2008
Tuesday, March 18, 2008
External Electric Field Effects on State Energy and Photoexcitation Dynamics of Diphenylpolyenes
External electric field effects on state energy and photoexcitation dynamics have been examined for para-substituted and unsubstituted all-trans-diphenylpolyenes doped in a film, based on the steady-state and picosecond time-resolved measurements of the field effects on absorption and fluorescence. The substitution dependence of the electroabsorption spectra shows that the dipole moment of the substituted stilbene in the Franck-Condon excited state becomes larger with increasing difference between the Hammet constants of the substituents. Fluorescence quantum yields of 4-(dimethylamino)-4'-nitrostilbene and 4-(dimethylamino)-4'-nitrodiphenylbutadiene are markedly reduced by an electric field, suggesting that the rates of the intramolecular charge transfer (CT) from the fluorescent state to the nonradiative CT state are accelerated by an external electric field. The magnitude of the field-induced decrease in fluorescence lifetime has been evaluated. The isomerization of the unsubstituted all-trans-diphenylpolyenes to the cis forms is shown to be a significant nonradiative pathway even in a film. Field-induced quenching of their fluorescence as well as field-induced decrease in fluorescence lifetime suggests that the trans to cis photoisomerization is enhanced by an electric field.
Friday, March 14, 2008
Synthesis of Regioregular Poly(p-phenylenevinylene)s by Horner Reaction and Their Regioregularity Characterization
A new synthetic route was developed to obtain highly regioregular poly[(2-methoxy-5-alkyloxy)-1,4-phenylenevinylene]s (PPVs) by the Horner reaction using asymmetrically functionalized monomers. The polymers showed good solubility in chlorobenzene at over 100
C. The high regioregularity of the polymers was confirmed by 1H NMR quantitative analysis using chlorobenzene-d5 as solvent, which was developed for the first time in this study. Assignment of the 1H NMR peaks was conducted by synthesizing four novel model compounds for PPV. UV-vis, fluorescence spectra, and XRD data revealed that these regioregular PPVs have higher crystallinity compared to regiorandom PPVs in the solid state.Sunday, February 17, 2008
Synthesis and properties of poly(arylenevinylene)s comprising of an electron-donating carbazole unit and an electron-accepting 2,1,3-benzothiadiazole
Two new soluble arylenevinylene-based polymers comprising of an electron-donating carbazole unit and an electron-accepting 2,1,3-benzothiadiazole (or fluorenone) unit in the main chain were synthesized by Heck polycondensation between 3,6-divinylene-9-decyl carbazole and 4,7-dibromo-2,1,3-benzothiadiazole (or 2,7-dibromofluorenone). In the toluene solution, a polymer with benzothiadiazole unit showed strong red photoluminescence, whereas the polymer with fluorenone unit showed white–yellow photoluminescence. The polymers had good thermal stability with 5 wt% loss temperature of more than 430 °C. Electrochemically, the polymers appeared to be reversible under reduction.
Polymer Volume 46, Issue 25, 28 November 2005, Pages 11927-11933
Alternating poly(pyridyl vinylene phenylene vinylene)s: synthesis and solid state organizations
Poly(pyridyl vinylene phenylene vinylenes) were synthesized by Heck coupling procedures. These materials display large red shifts in their optical absorption which upon protonation or alkylation of the pyridyl nitrogen. Some of the polymers were found to be liquid crystalline. The protonated or alkylated versions exhibit highly organized structures due to charge-transfer interactions between polymer chains.
doi:10.1016/S0040-4020(97)00975-7
doi:10.1016/S0040-4020(97)00975-7
Donor-acceptor copolymers for red- and near-infrared-emitting polymer light-emitting diodes
We report a comparative study of two organic soluble, vinylene-based, alternating donor-acceptor copolymers with 1,4-(2,5-dihexadecyloxyphenylene) as the donor; the acceptor is either a 2,5-linked pyridine or a 5,8-linked 2,3-diphenylpyrido[3,4-b]pyrazine. The polymers are synthesized via a Heck coupling methodology from a dihalo monomer and a divinyl monomer to yield number-average molecular weights of 16,000 g/mol for the pyridine polymer (PPyrPV) and 6500 g/mol for the pyridopyrazine polymer (PPyrPyrPV), with high solubility in common chlorinated solvents and lower solubility in less polar solvents (e.g., tetrahydrofuran). Thin-film measurements show band gaps of 2.2 and 1.8 eV for PPyrPV and PPyrPyrPV, respectively. Both polymers exhibit photoluminescence in solution and in the solid state and exhibit electroluminescence when incorporated into light-emitting diodes. In this case, a broad red emission centered at 690 nm for PPyrPV and a near-infrared emission centered at 800 nm for PPyrPyrPV have been observed
J. Polym. Sci. A Polym. Chem. Vol.43, 7 Pages: 1417-1431
Design, Synthesis, and Electroluminescent Property of CN-Poly(dihexylfluorenevinylene) for LEDs
A new green electroluminescence polymer, CN-poly(dihexylfluorenevinylene) (CN-PDHFV), which denotes poly[(9,9-dihexyl-9H-fluorene-2,7-diyl)(1-cyanoethene-1,2-diyl)(9,9-dihexyl-9H-fluorene-2,7-diyl)(2-cyaoethene-1,2-diyl)], was synthesized by condensation polymerization utilizing the Knoevenagel reaction. The resulting polymer exhibits good solubility in common organic solvents such as chloroform, THF, and ODCB. The polymer is also easily cast on a glass plate to green film. The UV-vis spectrum of the polymer exhibits characteristically a broad absorption band at 440 nm. This polymer shows photoluminescence around max = 535 nm (exciting wavelength 410 nm) and green electroluminescence around max = 530 nm. The current-voltage-luminance (I-V-L) characteristics of the polymer show a turn-on voltage of 4.8 V and a brightness of 600 cd/m2 at 5.8 V in the Al/polymer/PEDOT/ITO device. The highest efficiency was observed to be 0.85 lm/W at 5.6 V.
Macromolecules, 36 (19), 6970 -6975, 2003.
Tuesday, February 12, 2008
Thursday, January 17, 2008
Side Chain Influence on Electrochemical and Photovoltaic Properties of Yne-Containing Poly(phenylene vinylene)s
The electrochemical behaviour of four types of (phenylene ethynylene)-alt-(phenylene vinylene) hybrid polymers, 1, 2, 3, and 4 have been investigated with respect to the influence of the grafted alkoxy side chains. In the case of the fully substituted polymers 2, 3, and 4, the strong insulating nature of longer linear octadecyl or bulky branched 2-ethylhexyl side chains lowers the HOMO levels of the polymers thereby increasing the discrepancy, Eg, between the electrochemical, E, and the optical, E, bandgap energies. Thus it is not possible to establish a direct correlation between the open circuit voltage, VOC, of bulk heterojunction solar cell devices of the configuration glass substrate/ITO/PEDOT:PSS/polymer 3:PCBM(1:3, w/w)/LiF/Al and the HOMO energy levels of polymer 3 solely, as postulated in the literature. The photovoltaic (PV) parameters greatly depend on the grafted side chains.
Macromolecular Rapid Communications, 2005, 26, 1389 - 1394
Influence of the Conjugation Pattern on the Photophysical Properties of Alkoxy-Substituted PE/PV Hybrid Polymers
Alkoxy-substituted phenylene-ethynylene (PE)/phenylene-vinylene (PV) hybrid polymers of general constitutional structure (-Ar-CC-Ar-CH=CH-)n (2), (-Ar-CC-Ar-CH=CH-Ar-CC-)n (3), and (-Ar-CC-Ar-CC-Ar-CH=CH-Ar-CH=CH-)n (4) have been synthesized and characterized. Comparisons of their photophysical properties in solution as well as in solid state (photoconductivity, absorption, emission, and electroluminescence) with those of their corresponding alkoxy-substituted poly(phenylene-ethynylene) (1) and poly(phenylene-vinylene) (5) have been carried out. Large octadecyloxy groups were selected as side chains in order to reduce the effect of - stacking interaction on the properties of the polymers in the solid state. This resulted in easy detection of photoconductivity and higher fluorescence quantum yields in solid state. The hybrid conjugation pattern in 4 is more favorable for photoconductivity than that in 2. A red shift of the absorption and emission spectra in solution is observed from 1 over 2b, 3, and 4 to 5. LED devices of ITO/PEDOT/polymer/Ca configuration have been fabricated with all compounds, except 2a. The phenylvinylene side groups in 3 not only give rise to a red shift of the solid-state photoluminescence spectrum and electroluminescence spectrum (relative to 2b) but also bring about a decrease of the turn-on voltage and improve the electroluminescence efficiency for more than 100 times.
Macromolecules, 36 (25), 9303 -9312, 2003.
Stereocontrolled Synthesis and Characterization of cis-Poly(arylenevinylene)s
A highly stereocontrolled synthesis of five kinds of cis-poly[(arylenevinylene)-alt-(2,5-dioctyloxy-1,4-phenylenevinylene)]s has been accomplished by Suzuki-Miyaura-type polycondensation [arylene = p-phenylene (3af), m-phenylene (3bf), 4,4'-biphenylene (3cf), 2,7-fluorenylene (3df), 9,9-dihexyl-2,7-fluorenylene (3ef)]. Reactions of (Z,Z)-bis(2-bromoethenyl)arenes (1a-e) with 2,5-dioctyloxybenzene-1,4-diboronic acid (2fx) in toluene in the presence of Pd(PPh3)4 catalyst, aqueous KOH base, and Bu4NBr as a phase-transfer catalyst at 80 C for 24 h form 3af-ef with number-average molecular weight (Mn) of 5700-9500 in 77-99% yields. The stereoregularity of vinylene linkages in the polymer backbone has been found at least 95%. The starting monomers (1a-e) were prepared in almost geometrically pure forms (99% cis), either by ruthenium-catalyzed hydrosilylation of diethynylarenes followed by bromodesilylation of the resulting bis(2-bromoethenyl)arenes or by addition of bromine to arenediacrylic acids followed by debrominative decarboxylation promoted by Et3N. MALDI-TOF-MS analysis of cis-3af has revealed the presence of two types of polymers having different end groups. Type I polymer bears (Z)-4-(2-bromoethenyl)phenyl and 2,5-dioctyloxyphenyl group at each end, whereas type II polymer has 2,5-dioctyloxyphenyl groups at both ends. Type I polymer is successfully converted to type II polymer by palladium-catalyzed reaction with 2,5-dioctyloxybenzeneboronic acid to obtain cis-poly[(p-phenylenevinylene)-alt-(2,5-dioctyloxy-1,4-phenylenevinylene)] in a single form.
Macromolecules, 39 (6), 2039 -2048, 2006. 10.1021/ma052183l
Wednesday, January 16, 2008
A Novel Bipolar Electroluminescent Poly(arylene ethynylene) Consisting of Carbazole and Diethynylthiophene Units
A novel bipolar conjugated copolymer poly[(2, 5-diethynylthienylene)-alt-co-(9-hexyl-3,6-carbazole)] (PCT) bearing electron-affinitive moiety of 2,5-diethynylthiophene and hole-transport moiety of carbazole was synthesized via a Pd-catalyzed coupling reaction. The polymer possesses a weight average molecular weight of 23 000 with a polydispersity index of 2.5. PCT exhibits good thermal stability with a glass-transition temperature of 103°C and an onset decomposition temperature of 338°C. The HOMO and LUMO energy levels of PCT were determined to be -5.36 and -2.46 eV, respectively, using cyclic voltammetry. Single-layer and multilayer light-emitting diodes emit yellow light (peak at 580 nm). Double-layer electroluminescent device with the structure of ITO/copper phthalocyanine/PCT/Ca/Ag has an external quantum efficiency of 0.01%, higher than that of three-layer device with the structure of ITO/copper phthalocyanine/PCT/Alq3/Al, indicating that the electron injection is the limiting factor for the performance of PCT in polymer light-emitting diodes.
Macromolecular Chemistry and Physics, 201, 202, Issue 11 , Pages 2341 - 2345
Macromolecular Chemistry and Physics, 201, 202, Issue 11 , Pages 2341 - 2345
Synthesis of poly(fluorenevinylene-co-phenylenevinylene) by suzuki coupling
uzuki coupling modified by adding Ag2O instead of the Na2CO3 used in the original reaction protocol, was used as a synthetic tool for the synthesis of a copolymer in which 9,9-dialkylfluorene moieties were coupled to unsubstituted poly(p-phenylenevinylene) (PPV) units. The possibility of performing the polymerisations at moderate temperatures appears to be an advantage related to the use of Ag2O. The copolymer shows a [bar M ]w of 21 000 and [bar M ]w/[bar M ]n = 2.1 and is suitable for the construction of electroluminescent devices. Monolayer organic light-emitting diodes (OLEDs) have been built which emit greenish light.
Macromol. Chem. Phys. 2002, 203,1926-1930
Conjugated polymers for nonlinear optics. 1. Synthesis and properties of poly(aryleneethynylenevinylene)s
Rigid-rod conjugated poly(aryleneethynylenevinylene)s were prepared from diethynyl aromatic compounds containing alkoxy groups and trans,trans-1,4-bis(β-bromoviny ])benzene by palladium-catalyzed coupling reaction. Polymerizations were carried out in THF in the presence of Pd catalyst, CuI and diethyl amine and gave a series of poly(aryleneethynylenevinylene)s with weight average molecular weight up to 56,000. The characterization of polymers by IR, NMR, UV-Vis, thermogravimetry, DSC, optical microscopy and X-ray are reported. The polymers exhibited intense fluorescence in solution (THF) and absorption band shifted to longer wavelength in films of the polymers. Polymers with long alkoxy side chains showed good solubility in THF, CH2Cl2 and CHCl3.
Reactive and Functional Polymers, 1996, 30, 341-352
Reactive and Functional Polymers, 1996, 30, 341-352
Stereocontrolled Synthesis and Optical Properties of All-cis Poly(phenylene vinylenes) (PPVs): A Method for Direct Patterning of PPVs
Geometrically pure, all-cis poly(phenylene vinylenes) (PPVs) are synthesized by Suzuki-Miyaura-type polycondensation of 2,5-dioctyloxy-1,4-benzenediboronic acid with (Z,Z)-bis(2-bromoethenyl)benzenes, which are prepared by ruthenium-catalyzed (Z)-selective double hydrosilylation of diethynylbenzenes, followed by bromodesilylation of the resulting (Z,Z)-bis(2-silylethenyl)benzenes with N-bromosuccinimide. The all-cis PPVs thus obtained undergo one-way photoisomerization to the corresponding trans-PPVs both in solution and in the solid. This phenomenon is applied to direct microscale patterning of PPVs onto a quartz substrate.
J. Am. Chem. Soc., 127 (12), 4350 -4353, 2005. 10.1021/ja042853n
Tuesday, January 8, 2008
Synthesis and Characterization of Repeating Sequence Copolymers of Fluorene and Methylene Monomers
A series of well-defined multiblock (mb) copolymers consisting of alternating 9,9-dihexylfluorene and methylene segments has been prepared. Poly(9,9-dihexylfluorene-mb-methylene)s (PFMs) with repeat units of FxMy (x = 1-4, y = 10, 18 and x = 5-8, y = 18) were assembled by tandem metal-catalyzed acyclic diene metathesis (ADMET) polymerization/hydrogenation from ,-olefin bearing precursors. The polymers exhibited weight-average molecular weights ranging from Mw = 10 to 57 kDa. The PFMs exhibit photophysical properties, absorbance, and emission consistent with the length of the fluorene sequence. Glass and melting transition temperatures also increase with fluorene segment length.
Macromolecules, 41 (1), 31 -35, 2008. 10.1021/ma0703711
Monday, January 7, 2008
Friday, January 4, 2008
Synthesis and electronic properties of conjugated polymers based on rhenium or ruthenium dipyridophenazine complexes
wo series of luminescent conjugated polymers based on rhenium(I) or ruthenium(II) dipyridophenazine complexes have been synthesized by the palladium catalyzed coupling reaction using divinylbenzene and aromatic dibromides as the monomers. From the photoluminescence spectra, an energy transfer process between the conjugated backbone and the metal complexes is proposed. The ruthenium containing polymers were fabricated into light emitting devices because of their better film forming qualities. The electroluminescence (EL) of the polymers originated from the emission due to the *- or *-d transitions. Depending on the metal complex content, the polymers exhibit different absorption and EL spectra. The devices exhibit a turn-on voltage of 10 V and external quantum efficiency of 0.6%. From the cyclic voltammetry results, an additional oxidation couple was observed after the incorporation of the ruthenium complex which may contribute to the charge transport process. This was further supported by the charge mobilities measurement in which the electron and hole mobilities of the polymers are enhanced by the metal complex and are of the order of 10–4 cm2 V–1 s–1.
J. Mater. Chem., 1999, 9, 2103 - 2108
J. Mater. Chem., 1999, 9, 2103 - 2108
Synthesis and Characterization of Soluble and n-Dopable Poly(quinoxaline vinylene)s and Poly(pyridopyrazine vinylene)s with Relatively Small Band Gap
Synthesis and characterization of poly(quinoxaline vinylene)s and poly(pyridopyrazine vinylene)s with linear and branched aliphatic side chains are reported. The electron affinity of the polymers was measured with cyclic voltammetry (CV) and found to be highest for the pyridopyrazine vinylene polymers. Compared to CN-MEH-PPV, the pyridopyrazine vinylene polymers were easier to reduce, while the quinoxaline derivatives were harder. UV-vis absorption measurements showed that the polymers have relatively small band gaps.
Macromolecules, 35 (5), 1638 -1643, 2002
Macromolecules, 35 (5), 1638 -1643, 2002
Synthesis and characterization of new copolymers of thiophene and vinylene: Poly(thienylenevinylene)s and poly(terthienylenevinylene)s with thioether
Poly[3,4-bis(3-methylbutylthio)thienylenevinylene], poly[3,4-bis-(S)-(2-methylbutylthio)thienylenevinylene], poly[3,4-bis(3-methylbutylthio)-2,2:5,2-terthienylene-5,5-vinylene], and poly{3,4-bis-(S)-[2-methylbutylthio]-2,2:5,2-terthienylene-5,5-vinylene} have been synthesized. The synthesis starts from the thiophene monomers and trimers, which are formylated to give the corresponding dialdehydes. The dialdehydes are reductively polymerized using a McMurry coupling. The polymers are characterized by GPC, optical spectroscopy (FT-IR, UV-vis, circular dichroism spectroscopy and photoluminescence) and by proton and carbon NMR spectroscopy. The polymers are soluble in common organic solvents, such as THF, chloroform, toluene, benzene and 1,2-dichlorobenzene. The solvatochromism and thermochromism of the polymers in solution are investigated, while the optical activity of the polymers is used to investigate the supramolecular aggregation.
Journal of Polymer Science Part A: Polymer Chemistry, Volume 37, Issue 24 , Pages 4629 - 4639
Journal of Polymer Science Part A: Polymer Chemistry, Volume 37, Issue 24 , Pages 4629 - 4639
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