Comparative study of the optical,electrochemical, electrolumiscent,and photovoltaic properties of dendritic pendants modified poly(p‐phenylene vinylene)s

In this study, the optical, electrochemical, electrolumiscent, and photovoltaic properties of a series of poly(p‐phenylene vinylene) (PPV) derivatives bearing different dendritic pendants, poly{2‐[3′,5′‐bis(2″‐ethylhexyloxy)benzyloxy]‐1,4‐phenylenevinylene} (BE‐PPV), poly{2‐[2′,5′‐bis(3″,7″‐dimethyl)octyloxy]‐1,4‐phenylenevinylene} (BD‐PPV), poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV), poly{2‐[3′,5′‐bis(2″‐ethylhexyloxy)benzyloxy]‐1,4‐phenylenevinylene}‐co‐poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (BE‐co‐MEH‐PPV), and poly{2‐[2′,5′‐bis(3″,7″‐dimethyl)octyloxy]‐1,4‐phenylenevinylene}‐co‐poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (BD‐co‐MDMO‐PPV), were investigated. The steric pendants strongly affect the absorption spectra, photoluminescence (PL) sepctra, the onset oxidation/reduction potentials, and further affect the electrolumiscent and photovoltaic properties. Copolymerization can reduce the steric effect and improve the electrolumiscent and photovoltaic properties. The brightness of light‐emitting diodes base on copolymer BE‐co‐MEH‐PPV and BD‐co‐MDMO‐PPV reached 3988 and 3864 cd/m², respectively, much higher than that based on homopolymer BE‐PPV (523 cd/m²) and BD‐PPV (333 cd/m²), also higher than that based on MEH‐PPV (3788 cd/m²). The power conversion efficiency (PCE) of solar cells based on BE‐co‐MEH‐PPV and BD‐co‐MDMO‐PPV reached 1.41, 0.76%, respectively, much higher than that based on BE‐PPV (0.24%) and BD‐PPV (0.14%). Copyright © 2010 John Wiley & Sons, Ltd.     

Syntheses and electroluminescence properties of conjugated poly(p‐phenylene vinylene) derivatives bearing dendritic pendants

A series of new poly(p‐phenylene vinylene) derivatives with different dendritic pendants—poly{2‐[3′,5′‐bis(2″‐ethylhexyloxy)benzyloxy]‐1,4‐phenylenevinylene} (BE–PPV), poly{2‐[3′,5′‐bis(3″,7″‐dimethyl)octyloxy]‐1,4‐phenylenevinylene} (BD–PPV), poly(2‐{3′,5′‐bis[3″,5″‐bis(2?‐ethylhexyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene) (BBE–PPV), poly(2‐{3′,5′‐bis[3″,5″‐bis(3?,7?‐dimethyloctyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene) (BBD–PPV), and poly[(2‐{3′,5′‐bis[3″,5″‐bis(2?‐ethylhexyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene)‐co‐(2‐{3′,5′‐bis[3″,5″‐bis(3?,7?‐dimethyloctyloxy)benzyloxy]benzyloxy}‐1,4‐phenylenevinylene)] (BBE‐co‐BBD–PPV; 1:1)—were successfully synthesized according to the Gilch route. The structures and properties of the monomers and the resulting conjugated polymers were characterized with ¹H and ¹³C NMR, elemental analysis, gel permeation chromatography, thermogravimetric analysis, ultraviolet–visible absorption spectroscopy, photoluminescence, and electroluminescence spectroscopy. The obtained polymers possessed excellent solubility in common solvents and good thermal stability, with a 5% weight loss temperature of more than 328 °C. The weight‐average molecular weights and polydispersity indices of BE–PPV, BD–PPV, BBE–PPV, BBD–PPV, and BBE‐co‐BBD–PPV (1:1) were in the range of 1.33–2.28 × 10⁵ and 1.35–1.53, respectively. Double‐layer light‐emitting diodes (LEDs) with the configuration of indium tin oxide/polymer/tris(8‐hydroxyquinoline) aluminum/Mg:Ag/Ag devices were fabricated, and they emitted green‐yellow light. The turn‐on voltages of BE–PPV, BD–PPV, BBE–PPV, BBD–PPV, and BBE‐co‐BBD–PPV (1:1) were approximately 5.6, 5.9, 5.5, 5.2, and 4.8 V, respectively. The LED devices of BE–PPV and BD–PPV possessed the highest electroluminescent performance; they exhibited maximum luminance with about 860 cd/m² at 12.8 V and 651 cd/m² at 13 V, respectively. The maximum luminescence efficiency of BE–PPV and BD–PPV was in the range of 0.37–0.40 cd/A. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3126–3140, 2005     

Synthesis and characterization of diphenylaminodiphenyl stryl based alternating copolymers

Diphenylaminobiphenylated stryl based alternating copolymers with phenyl or fluorene, which were expected to have a terphenylene vinylene backbone containing an (N,N‐diphenylamino)biphenyl pendant and a phenyl/fluorene/phenylene vinylene backbone containing an (N,N‐diphenylamino)biphenyl pendant, were synthesized by a Suzuki coupling reaction. The obtained copolymers were confirmed with various types of spectroscopy. The alternating copolymers showed good hole‐injection properties because of their low oxidation potential and good solubility and high thermal stability with a high glass‐transition temperature. The alternating copolymers showed blue emissions because of the adjusted conjugation lengths; the maximum wavelength was 460 nm for poly{4,4′‐biphenylene‐α‐[4″‐(N,N′‐diphenylamino)diphenyl]vinylene‐alt‐5‐(2′‐ethylhexyloxy)‐2‐methoxybenzene} and 487 nm for poly{4,4′‐biphenylene‐α‐[4″‐(N,N′‐diphenylamino)diphenyl] vinylene‐alt‐9,9‐dihexylfluorene}. The maximum brightness of indium tin oxide/poly(3,4‐ethylene dioxythiophene)/polymer/LiF/Al devices with poly{4,4′‐biphenylene‐α‐[4″‐(N,N′‐diphenylamino)diphenyl]vinylene‐alt‐5‐(2′‐ethylhexyloxy)‐2‐methoxybenzene} or poly{4,4′‐biphenylene‐α‐[4″‐(N,N′‐diphenylamino)diphenyl]vinylene‐alt‐9,9‐dihexylfluorene} as the emitting layer was 250 or 1000 cd/m², respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 341–347, 2007     

Novel route to poly(p‐phenylene vinylene) polymers

Poly(p‐phenylene vinylene) (PPV), poly(2,5‐dioctyl‐p‐phenylene vinylene) (PDOPPV), and poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylene vinylene] (MEHPPV) were synthesized by a liquid–solid two‐phase reaction. The liquid phase was tetrahydrofuran containing 1,4‐bis(bromomethyl)benzene, 1,4‐bis(chloromethyl)‐2,5‐dioctylbenzene, or 1,4‐bis(chloromethyl)‐2‐methoxyl‐5‐(2′‐ethylhexyloxy)benzene as the monomer and a certain amount of tetrabutylammonium bromide as a phase‐transfer catalyst. The solid phase consisted of potassium hydroxide particles with diameters smaller than 2 mm. The experimental results demonstrated that the reaction conversions of PPV and PDOPPV were fairly high (～65%), but the conversion of MEHPPV was only 45%. Moreover, gelation was found in the polymerization processes. As a result, PPV was insoluble and PDOPPV and MEHPPV were partially soluble in the usual organic solvents, such as tetrahydrofuran and chloroform. Soluble PDOPPV and MEHPPV were obtained with chloromethylbenzene or bromomethylbenzene as a retardant regent. The molar mass of soluble PDOPPV was measured to be 2 × 10⁴ g mol^?1, and that of MEHPPV was 6 × 10⁴ g mol^?1. A thin, compact film of MEHPPV was formed via spin coating, and it emitted a yellow light. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 449–455, 2003     

Synthesis,Electrochemical, and Optical Properties of a Novel PPV/PPE Block‐Copolymer

Summary: A novel poly(p‐phenylene vinylene) (PPV)/poly(p‐phenylene ethynylene) (PPE) block‐copolymer was synthesized by a cross‐coupling polycondensation with Pd(PPh₃)₂Cl₂ and a phase‐transfer catalyst, and was confirmed by ¹H NMR and IR spectroscopy and elemental analysis. The thermal, electrochemical, and photoluminescent properties of the new copolymer have been investigated. The incorporation of triple bonds into the cyano‐substituted PPV (CN‐PPV) backbone leads to higher oxidation and reduction potentials than poly(2‐methoxy‐5‐(2‐ethylhexyloxy)‐p‐phenylene vinylene) (MEH‐PPV) and CN‐PPV, potentially making the copolymer a good electron‐transporting material for use in a light‐emitting‐diode device.

The cyclic voltammogram of the novel poly(p‐phenylene vinylene) (PPV)/poly(p‐phenylene ethynylene) (PPE) block‐copolymer synthesized here.     

Green‐emitting poly[(1,3‐phenylenevinylene)‐alt‐ (1,4‐phenylenevinylene)]s: Effect of the substitution patterns on the optical properties

Green‐emitting substituted poly[(2‐hexyloxy‐5‐methyl‐1,3‐phenylenevinylene)‐alt‐(2,5‐dihexyloxy‐1,4‐phenylenevinylene)]s ( 6 ) were synthesized via the Wittig–Horner reaction. The polymers were yellow resins with molecular weights of 10,600. The ultraviolet–visible (UV–vis) absorption of 6 (λ_max = 332 or 415 nm) was about 30 nm redshifted from that of poly[(2‐hexyloxy‐5‐methyl‐1,3‐phenylenevinylene)‐alt‐(1,4‐phenylenevinylene)] ( 2 ) but was only 5 nm redshifted with respect to that of poly[(1,3‐phenylenevinylene)‐alt‐(2,5‐dihexyloxy‐1,4‐phenylenevinylene)] ( 1 ). A comparison of the optical properties of 1 , 2 , and 6 showed that substitution on m‐ or p‐phenylene could slightly affect their energy gap and luminescence efficiency, thereby fine‐tuning the optical properties of the poly[(m‐phenylene vinylene)‐alt‐(p‐phenylene vinylene)] materials. The vibronic structures were assigned with the aid of low‐temperature UV–vis and fluorescence spectroscopy. Light‐emitting‐diode devices with 6 produced a green electroluminescence output (emission λ_max ～ 533 nm) with an external quantum efficiency of 0.32%. Substitution at m‐phenylene appeared to be effective in perturbing the charge‐injection process in LED devices. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1820–1829, 2004     

A phenylenevinylene‐thiophene‐phenyleneethynylene copolymer: synthesis,characterization, and photovoltaic properties

A phenylenevinylene‐thiophene‐phenyleneethynylene copolymer, poly{[1′,4′‐bis‐(thienyl‐vinyl)]‐2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylene‐vinylene‐alt‐1,4‐dioctyloxyl‐phenyleneethynylene}(PTPPV‐ PPE), was synthesized by the Sonogashira Pd‐catalyzed cross‐coupling reaction. The copolymer possesses higher thermal decomposition temperature (T_d = 382°C) compared with poly{[1′,4′‐bis‐ (thienyl‐vinyl)]‐2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylene‐vinylene} (PTPPV). The absorption and photoluminescence (PL) peaks of PTPPV‐PPE solution and solid film locate in between those of the homopolymers of PTPPV and poly(1,4‐dioctyloxyl‐phenyleneethynylene) (PPE), and closer to that of PTPPV. Photovoltaic cell was fabricated based on the blend of PTPPV‐PPE and PCBM with a weight ratio of 1:1. The primary result shows an open circuit voltage (V_oc) of 0.72 V which is higher than that of the PTPPV (0.67 V), and a power conversion efficiency (PCE) of 0.3% under the illumination of AM1.5, 100 mW/cm² which is much better than that of PPEs. Copyright © 2008 John Wiley & Sons, Ltd.     

NMR signal assignment of cis/trans‐conformational segments in MEH‐CN‐PPV

Poly[2‐(2′‐ethylhexyloxy)‐5‐methoxy‐1,4‐phenylene‐(1‐cyanovinylene)] MEH‐CN‐PPV and its all‐trans model compound 1,4‐bis(α‐cyanostyryl)‐2‐(2‐ethylhexyloxy)‐5‐methyloxybenzene were synthesized via Knoevenagel condensation. All‐cis isomer and cis–trans isomer of 1,4‐bis(α‐cyanostyryl)‐2‐(2‐ethylhexyloxy)‐5‐methyloxybenzene were prepared by the photoisomerization reaction. Comparison of the ¹H NMR spectra between MEH‐CN‐PPV and three model compounds proved the occurrence of cis‐vinylene in the backbone of MEH‐CN‐PPV. According to the ratio between the cis‐vinylene signal and trans‐vinylene signal, the content of the cis‐vinylene could be estimated to be 15% in MEH‐CN‐PPV. This large cis‐vinylene content came from the rapid photochemical isomerization of cyanovinylene and was likely relative to the poor electroluminescence property of MEH‐CN‐PPV. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1105–1113, 2008     

Synthesis of new polyfluorene copolymers with a comonomer containing triphenylamine units and their applications in white‐light‐emitting diodes

Novel conjugated polyfluorene copolymers, poly[9,9‐dihexylfluorene‐2,7‐diyl‐co‐(2,5‐bis(4′‐diphenylaminostyryl)‐phenylene‐1,4‐diyl)]s (PGs), have been synthesized by nickel(0)‐mediated polymerization from 2,7‐dibromo‐9,9‐dihexylfluorene and 1,4′‐dibromo‐2,5‐bis(4‐diphenylaminostyryl)benzene with various molar ratios of the monomers. Because of the incorporation of triphenylamine (TPA) moieties, PGs exhibit much higher HOMO levels than the corresponding polyfluorene homopolymers and are able to facilitate hole injection into the polymer layer from the anode electrode in light‐emitting diodes. Conventional polymeric light‐emitting devices with the configuration ITO/PEDOT:PSS/polymer/Ca/Al have been fabricated. A light‐emitting device produced with one of the PG copolymers (PG10) as the emitting layer exhibited a voltage‐independent and stable bluish‐green emission with color coordinates of (0.22, 0.42) at 5 V. The maximum brightness and current efficiency of the PG10 device were 3370 cd/m² (at 9.6 V) and 0.6 cd/A, respectively. To realize a white polymeric light‐emitting diode, PG10 as the host material was blended with 1.0 wt % of a red‐light‐emitting polymer, poly[9,9‐dioctylfluorene‐2,7‐diyl‐alt‐2,5‐bis(2‐thienyl‐2‐cyanovinyl)‐1‐(2′‐ethylhexyloxy)‐4‐methoxybenzene‐5′,5′‐diyl] (PFR4‐S), and poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV). The device based on PG10:PFR4‐S showed an almost perfect pure white electroluminescence emission, with Commission Internationale de l'Eclairage (CIE) coordinates of (0.33, 0.36) at 8 V; for the PG10:MEH‐PPV device, the CIE coordinates at this voltage were (0.30, 0.40) with a maximum brightness of 1930 cd/m². Moreover, the white‐light emission from the PG10:PFR4‐S device was stable even at different driving voltages and had CIE coordinates of (0.34, 0.36) at 6 V and (0.31, 0.35) at 10 V. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1199–1209, 2007     

Blue‐emitting poly(1,3‐phenylenevinylene) derivatives: Effect of substitution patterns on optical properties

Blue‐emitting poly{[5‐(diphenylamino)‐1,3‐phenylenevinylene]‐alt‐(2‐hexyloxy‐5‐methyl‐1,3‐phenylenevinylene)} ( 3 ), poly{[5‐bis‐(4‐butyl‐phenylamino)‐1,3‐phenylenevinylene]‐alt‐(1,3‐phenylene vinylene)} ( 4 ), and poly(2‐hexyloxy‐5‐methyl‐1,3‐phenylenevinylene) ( 5 ) were synthesized by the Wittig–Horner reaction. Although polymers 3–5 possess fluorescent quantum yields of only 13–34% in tetrahydrofuran solution, their films appear to be highly luminescent. Attachments of substituents tuned the emission color of thin films to the desirable blue region (λ_max = 462–477 nm). Double‐layer light‐emitting‐diode devices with 3 and 5 as an emissive layer produced blue emission (λ_em = 474 and 477 nm) with turn‐on voltages of 8 and 11 V, respectively. The external quantum efficiencies were up to 0.13%. © 2005Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2800–2809, 2005     

High electroluminescent properties of conjugated copolymers from poly[9,9‐dioctylfluorenyl‐2,7‐vinylene]‐co‐(2‐(3‐dimethyldodecylsilylphenyl)‐1,4‐phenylene vinylene)] for light‐emitting diode applications

A new series of copolymers with high brightness and luminance efficiency were synthesized using the Gilch polymerization method, and their electro‐optical properties were investigated. The weight‐average molecular weights (M_w) and polydispersities of the synthesized poly(9,9‐dioctylfluorenyl‐2,7‐vinylene) [poly(FV)], poly[2‐(3‐dimethyldodecylsilylphenyl)‐1,4‐phenylenevinylene] [poly(m‐SiPhPV)], and poly[9,9‐di‐n‐octylfluorenyl‐2,7‐vinylene]‐co‐(2‐(3‐dimethyldodecylsilylphenyl)‐1,4‐phenylene vinylene)] [poly(FV‐co‐m‐SiPhPV)] were found to be in the ranges of (8.7–32.6) × 10⁴ and 2.3–5.4, respectively. It was found that the electro‐optical properties of the copolymers could be adjusted by controlling the feed ratios of the comonomers. Thin films of poly(FV), poly(m‐SiPhPV), and poly(FV‐co‐m‐SiPhPV) were found to exhibit photoluminescence quantum yields between 21% and 42%, which are higher than those of MEH‐PPV. Light‐emitting diodes were fabricated in ITO/PEDOT/light‐emitting polymer/cathode configurations using either double layer (LiF/Al) or triple layer (Alq₃/LiF/Al) cathode structures. The performance of the polymer light‐emitting diodes (PLEDs) with triple layer cathodes was found to be better than that of the PLEDs with double layer cathodes in poly(FV) and poly(FV‐co‐m‐SiPhPV). The turn‐on voltages of the PLEDs were in the range of 4.5–6.0 V, with maximum brightness and luminance efficiency up to 9691 cd/m² at 16 V and 3.27 cd/A at 13 V, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5062–5071, 2005     

Synthesis and characterization of poly(fluorene)‐based copolymer containing triphenylamine group

The copolymers that are composed of poly(fluorene) (PF), poly(p‐phenylene), and Poly(p‐phenylenevinylene) as backbone and a large 4′‐(N,N′‐diphenylamino)diphenyl or 4′‐(N,N′‐diphenylamino)phenyl as pendent group were synthesized by the nickel(0)‐mediated polycoupling. The composition of the obtained copolymers was confirmed by H NMR. All the copolymers possessed a high weight‐average molecular weight and good solubility in common organic solvents. As the content of triphenyl amine pendants increases, the copolymers showed increased thermal stability due to increased glass transition temperature and increased hole injection ability because of decreased onset of the oxidation potential. In the photoluminescence spectra of copolymers, poly (BDAV₃₀‐co‐DHF₇₀) and poly(BDAPV₃₀‐co‐DHF₇₀) showed efficient energy transfer. indium tin oxide/poly(styrene sulfonate)‐doped poly(3,4‐ethylene dioxythiophene)/poly (BDAV₃₀‐co‐DHF₇₀)/LiF/Al device showed maximum brightness of 2267 cd/m² and efficiency of 0.80 cd/A, with turn‐on voltage at 9.1 V. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 172–182, 2006     

Cationic,water‐soluble,fluorene‐containing poly(arylene ethynylene)s: Effects of water solubility on aggregation,photoluminescence efficiency,and amplified fluorescence quenching in aqueous solutions

Three novel fluorene‐containing poly(arylene ethynylene)s with amino‐functionalized side groups were synthesized through the Sonogashira reaction. They were poly{9,9‐bis[6′‐(N,N‐diethylamino)hexyl]‐2,7‐fluorenylene ethynylene}‐alt‐co‐{2,5‐bis[3′‐(N,N‐diethylamino)‐1′‐oxapropyl]‐1,4‐phenylene} ( P1 ), poly{9,9‐bis[6′‐(N,N‐diethylamino)hexyl]‐2,7‐fluorenylene ethynylene} ( P2 ), and poly({9,9‐bis[6′‐(N,N‐diethylamino)hexyl]‐2,7‐fluorenylene ethynylene}‐alt‐co‐(1,4‐phenylene)) ( P3 ). Through the postquaternization treatment of P1 – P3 with methyl iodide, we obtained their cationic water‐soluble conjugated polyelectrolytes (WSCPs): P1′ – P3′ . The water solubility was gradually improved from P3′ to P1′ with increasing contents of hydrophilic side chains. After examining the ultraviolet–visible absorption and photoluminescence (PL) spectra, fluorescence lifetimes, and dynamic light scattering data, we propose that with the reduction of the water solubility from P1′ to P3′ , they exhibited a gradually increased degree of aggregation in H₂O. The PL quantum yields of P1′ – P3′ in H₂O displayed a decreasing tendency consistent with the increased degree of aggregation, suggesting that the pronounced degree of aggregation was an important reason for the low PL quantum yields of WSCPs in H₂O. Two structurally analogous water‐soluble trimers of P2′ and P3′ , model compounds 2,7‐bis(9″,9″‐bis{6‴‐[(N,N‐diethyl)‐N‐methylammonium] hexyl}‐2″‐fluorenylethynyl)‐9,9‐bis{6′‐[(N,N‐diethyl)‐N‐methylammonium]hexyl}fluorene hexaiodide and 1,4‐bis(9′,9′‐bis{6″‐[(N,N‐diethyl)‐N‐methylammonium]hexyl}‐2′‐fluorenylethynyl)benzene tetraiodide, were synthesized. The amplified fluorescence quenching of these WSCPs by Fe(CN)₆⁴⁻ in H₂O was studied by comparison with a corresponding analogous trimer. The effects of aggregation on the fluorescence quenching may be two‐edged in these cases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5778–5794, 2006     

A solution‐processible poly(p‐phenylene vinylene) without alkyl substitution: Introducing the cis‐vinylene segments in polymer chain for improved solubility,blue emission,and high efficiency

A soluble all‐aromatic poly(2,5‐diphenyl‐1,4‐phenylenevinylene) (2,5‐DP‐PPV) is synthesized by utilizing aromatic phosphonium and aldehyde monomers through Wittig reaction. The H¹ NMR and FTIR measurements indicate that over 50% content of cis‐vinylene units exist in polymer backbone. The diphenyl‐substituted benzaldehyde monomer plays an important role to enhance cis‐products (Z‐selectivity) in Wittig reactions. The twisted cis‐segments in polymer backbone reduce the interchain interactions and enhance the solubility of such all‐aromatic PPV derivative in common organic solvents. 2,5‐DP‐PPV exhibits good solubility in common organic solvents, such as tetrahydrofuran and chloroform. The polymer film exhibits a blue light emission (λ_max = 485 nm) and a very high photoluminescence efficiency of 78%. The cis‐trans photo isomerization of this polymer in solution and the impact on the optical properties are also investigated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5242–5250, 2008     

Synthesis of Poly[2‐decyloxy‐5‐(4′‐tert‐butylphenyl)‐1,4‐phenylenevinylene] as a Light Emitting Material

In this study, a new electroluminescent poly(2‐decyloxy‐5‐(4′‐tert‐butylphenyl)‐1,4‐phenylene‐vinylene) (designated as DBP‐PPV) with no tolane‐bis–benzyl (TBB) structure defect was prepared by dehydrohalogenation of 1,4‐bisbromomethyl‐2‐decyloxy‐5‐(4′‐tert‐butyl‐phenyl) benzene (as monomer). The monomer bearing decyloxy and 4′‐tert‐butylphenyl substituents was synthesized via alkylation, bromination and Suzuki coupling reactions. The two asymmetric substituents of the monomer can suppress the formation of TBB defect during polymerization process and make the resultant polymer be soluble in common organic solvents. The structure and properties of DBP‐PPV were examined by ¹H‐NMR, FT‐IR, UV/Vis, TGA and photoluminescence (PL) analyses. Moreover, with the DBP‐PPV acting as a light‐emitting polymer, a device with sequential lamination of ITO/PEDOT/DBP‐PPV/Ca/Ag was fabricated. The electroluminescence (EL) spectrum of the device showed a maximum emission at around 546 nm, corresponding to a yellowish‐green light. The device showed a turn‐on voltage of about 8.4 V and a maximum luminescence efficiency of 0.11 cd/A at an applied voltage of 12 V.     

Copoly(p‐phenylene)s containing bipolar triphenylamine and 1,2,4‐triazole groups: Synthesis,optoelectronic properties,and applications

Two novel copoly(p‐phenylene)s ( P1 – P2 ) containing bipolar groups (12.8 and 6.8 mol %, respectively), directly linked hole transporting triphenylamine and electron transporting aromatic 1,2,4‐triazole, were synthesized to enhance electroluminescence (EL) of poly(p‐phenylene vinylene) (PPV) derivatives. The bipolar groups not only enhance thermal stability but also promote electron affinity and hole affinity of the resulting copoly(p‐phenylene)s. Blending the bipolar copoly‐(p‐phenylene)s ( P1 – P2 ) with PPV derivatives ( d6‐PPV ) as an emitting layer effectively improve the emission efficiency of its electroluminescent devices [indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene) (PEDOT):poly(styrenesulfonate) (PSS)/polymer blend/Ca (50 nm)/Al (100 nm)]. The maximum luminance and maximum luminance efficiency were significantly enhanced from 310 cd m^?2 and 0.03 cd A^?1 ( d6‐PPV ‐based device) to 1450 cd m^?2 and 0.20 cd A^?1 (blend device with d6‐PPV / P1 = 96/4 containing ～0.5 wt % of bipolar groups), respectively. Our results demonstrate the efficacy of the copoly(p‐phenylene)s with bipolar groups in enhancing EL of PPV derivatives. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Reactive intermediates in the initiation step of the photo‐oxidation of MDMO‐PPV

Because oxygen cannot be fully eliminated from organic solar cells, the occurrence of oxidative photo‐degradation of the device in operating conditions has to be considered. Polyphenylene‐vinylene‐based photovoltaic devices have a short lifetime that currently limits their applications. In this article, we focus on various transient species that are potentially involved in the initiation step of the photo‐oxidation of poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (MDMO‐PPV). The role of the transient species was investigated by a combination of quenching and sensitization experiments. Complementary information was obtained by transient absorption spectroscopy. Results evidenced the fact that ¹O₂ was not the principal reactive intermediate involved in the photo‐oxidation of MDMO‐PPV. This result was in contradiction with previous reports. It was shown that the MDMO‐PPV^?+ radical cation was generated after excitation. The presence of oxygen and the photo‐aging favored the formation of the radical cation, suggesting that oxygen and photoproducts act as electron acceptors. The charged radicals formed are likely to evolve and give radicals that initiate the oxidation of the polymer by abstraction of the labile hydrogen in α position of the ether function and by addition on the double bonds. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6044–6052, 2009     

Synthesis and electrochemical and electroluminescent properties of N‐phenylcarbazole‐substituted poly(p‐phenylenevinylene)

An N‐phenylcarbazole‐containing poly(p‐phenylenevinylene) (PPV), poly[(2‐(4′‐carbazol‐9‐yl‐phenyl)‐5‐octyloxy‐1,4‐phenylenevinylene)‐alt‐(2‐(2′‐ethylhexyloxy)‐5‐methoxy‐1,4‐phenylenevinylene)] (Cz‐PPV), was synthesized, and its optical, electrochemical, and electroluminescent properties were studied. The molecular structures of the key intermediates, the carbazole‐containing boronic ester and the dialdehyde monomer, were crystallographically characterized. The polymer was soluble in common organic solvents and exhibited good thermal stability with a 5% weight loss at temperatures above 420 °C in nitrogen. A cyclic voltammogram showed the oxidation peak potentials of both the pendant carbazole group and the PPV main chain, indicating that the hole‐injection ability of the polymer would be improved by the introduction of the carbazole‐functional group. A single‐layer light‐emitting diode (LED) with a simple configuration of indium tin oxide (ITO)/Cz‐PPV (80 nm)/Ca/Al exhibited a bright yellow emission with a brightness of 1560 cd/m² at a bias of 11 V and a current density of 565 mA/cm². A double‐layer LED device with the configuration of ITO/poly(3,4‐ethylenedioxy‐2,5‐thiophene):poly (styrenesulfonic acid) (60 nm)/Cz‐PPV (80 nm)/Ca/Al gave a low turn‐on voltage at 3 V and a maximum brightness of 6600 cd/m² at a bias of 8 V. The maximum electroluminescent efficiency corresponding to the double‐layer device was 1.15 cd/A, 0.42 lm/W, and 0.5%. The desired electroluminescence results demonstrated that the incorporation of hole‐transporting functional groups into the PPVs was effective for enhancing the electroluminescent performance. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5765–5773, 2005     

High red,green, and blue color purity electroluminescence from MEH‐PPV and polyalkyfluorenes‐based bright white polymer light emitting displays

A series of white polymer light emitting displays (PLEDs) based on a polymer blend of polyalkylfluorenes and poly(2‐methoxy‐5,2′‐ethyl‐hexyloxy‐1,4‐phenylene vinylene) (MEH‐PPV) was developed. MEH‐PPV or red light emitting alkyfluorene copolymer (PFR) was blended with blue light emitting alkyfluorene copolymer (PFB), and MEH‐PPV was blended with both green light emitting alkyfluorene copolymer (PFG) and PFB to generate white light emission PLEDs. Low turn on voltage (2.7 V), high brightness (12,149 nits), high efficiency (4.0 cd/A, 4.0 lm/W), and good color purity (Commission Internationale de L'Eclairage (CIE_x,y) co‐ordinates (0.32, 0.34)) were obtained for the white PLEDs based on the PFB and MEH‐PPV polymer blend. Exciplex formation in the interface between PFR and PFB induced a new green emission peak for these two components based white PLEDs. As a result, strong white emission (4078 nits) was obtained by mixing the red, green, and blue (RGB) three primary colors. High color purity of blue (CIE, x = 0.14, y = 0.08), green (CIE, x = 0.32, y = 0.64) and red (CIE, x = 0.67, y = 0.33) emissions was achieved for white PLEDs combining with dielectric interference color‐filters. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 330–341, 2007     

Poly[(2‐alkoxy‐5‐methyl‐1,3‐phenylene vinylene)‐alt‐(phenylene vinylene)] derivatives with different contents of cis‐ and trans‐olefins: The effect of the olefin bond geometry and conjugation length on luminescence

Poly[(2‐alkyloxy‐5‐methyl‐1,3‐phenylenevinylene)‐alt‐(1,3‐phenylenevinylene)]s ( 8 ) and poly[(2‐alkyloxy‐5‐methyl‐1,3‐phenylenevinylene)‐alt‐(1,4‐phenylenevinylene)]s ( 10 ) were synthesized by the Wittig reaction to provide materials containing 45–62% cis‐vinylene bonds. The optical characteristics of 8 and 10 were compared with those of their respective isomers, 3 and 4 , the cis‐vinylene contents of which were significantly lower (9–16%). Although a greater fraction of cis‐CH?CH linkages caused the absorption maximum (λ_max) of 8 and 10 to be slightly blueshifted (by ～3–6 nm) from that of 3 and 4 , the impact of the vinylene bond geometry appeared to be negligible on their fluorescence spectra. The fluorescence quantum efficiencies of 8 and 10 were estimated to be approximately 0.25 and 0.72, respectively. Both 8 (λ_max ≈ 445 or 462 nm) and 10 (λ_max ≈ 480 or 506 nm) were electroluminescent, showing effective color tuning by the controlled insertion of m‐phenylene moieties. The external electroluminescence quantum efficiencies were determined to be 4.26 × 10^?3% for 8 and 0.63% for 10 . The cis/trans‐vinylene bond ratio had a great impact on the electroluminescence device performance of 8 but a much smaller impact on the performance of 10 . © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 303–316, 2004