Fabrication and characterization of multilayer films from amphiphilic poly(p-phenylene)s

Over the past two decades, considerable efforts have been devoted to the development of conjugated polymeric materials for electronic applications due to the tunability of their properties through variation of their chemical structure. The LB technique is one of the most effective and precise methods for controlling the organization and thereby the properties of polymer films at the nanoscale for device fabrication. A detailed study was performed on the Langmuir-Schaefer (LS) monolayer and Langmuir-Blodgett-Kuhn (LBK) multilayer formation of newly designed conjugated poly(p-phenylene)s (C(n)PPPOH), incorporated with alkoxy groups with different chain lengths (C(6)H(13)O-, C(12)H(25)O-, and C(18)H(37)O-) and hydroxyl groups on the polymer backbone. The monolayer formed at the air-water interface was characterized using surface pressure-area isotherms, including hysteresis measurements. The films were then transferred to different hydrophilic solid substrates and analyzed using surface plasmon resonance spectroscopy, UV-vis spectroscopy, fluorescence spectroscopy, and AFM measurements. The results showed that the polymer with a short alkoxy chain (C(6)PPPOH) forms uniform monolayers at the air-water interface and can be transferred as multilayer films compared to C(12)PPPOH and C(18)PPPOH. The observed film thicknesses measured by SPR and AFM studies were similar to the theoretical value obtained in the case of C(6)PPPOH, whereas this was not the case with the other two polymers. The present study shows that the polymer C(n)PPPOH with short alkoxy chain can be transferred onto different solid substrates for device fabrication with molecular level control.     

Ultrathin conjugated polymer network films of carbazole functionalized poly(p-phenylenes) via electropolymerization

Ultrathin films of a cross-linked and chemically distinct conjugated poly(p-phenylene) network via electropolymerization are described. The amphiphilic network precursor was synthesized by incorporating the alkoxy carbazole group (-O(CH2)5Cb) to a poly(p-phenylene) (C6PPPOH) backbone. In order to investigate the combined thin film electrochemical and photophysical properties of poly(p-phenylene)s and polycarbazole conjugated polymers, C6PPPC5Cb was deposited on substrates using the Langmuir Blodgett Kuhn (LBK) method. The monolayer isotherm of the polymer, C6PPPC5Cb, showed a liquid expanded region slightly different from the parent polymer C6PPPOH. Multilayers (up to 30 layers) were transferred to different substrates such as quartz, gold coated LaSFN9 and ITO substrates for analysis. For conversion to a conjugated polymer network (CPN) film, the electroactive carbazole group was electropolymerized using cyclic voltammetry (CV) resulting in polycarbazole linking units. The differences in the film properties and corresponding changes in the electrochemical behavior indicate the importance of film thickness and electron/ion transport process in cross linked network films. From the electrochemical studies, the scan rate was found to have a considerable effect on electropolymerization with higher oxidation and reduction peak values found for the rigid network polymer compared to the uncrosslinked polymers.     

烷基和烷氧基取代聚噻吩的合成、表征与光电性能

Fe(Ⅲ )氧化催化法合成了 4种聚噻吩衍生物 ,3 十二烷基聚噻吩 (Pat12 ) ,3 辛氧基聚噻吩 (Paot8) ,3,4 二 (十二烷基 )聚噻吩 (Pat12 12 )和 3 (十二烷基 )噻吩 3 (辛氧基 )噻吩共聚物 (CoPt12 o8) .发现这些衍生物易溶于多种常用有机溶剂 .用GPC法测定了各聚合物分子量 ,用1 H NMR法表征了各聚合物化学结构 .对比研究了这些聚合物紫外 可见吸收性能 ,光致发光性能和能隙 .对其电致发光性能进行测定的结果 ,得到了Pat12 ,Pat12 12和Paot8的电致发光光谱 .发射峰分别为 6 70nm ,5 6 0nm和 6 4 0nm .发光颜色分别为红色 ,黄色和红橙色 .聚合物的光电性能与主链电子结构有密切关系 .探讨了取代基种类和数量对聚合物能带结构 ,光电性能的影响 .     

基于1-(4-己氧)苯和2,4,6-三苯基-1,3,5-三嗪功能化芴单元的聚合物蓝光材料的合成与表征

以聚(9,9-二己烷芴)(1)和聚(9,9-二(1-(4-己氧)苯)芴)(2)作为参照物,通过Suzuki偶联反应合成了侧链9位碳含有4-己氧基苯和2,4,6-三苯基-1,3,5-三嗪单元的芴共聚物3.聚合物1,2和3固体粉末的5%质量热损失温度分别是274,318和401℃,玻璃化转变温度分别是91,120和139℃.聚合物1,2和3在甲苯溶液中的最大吸收峰和荧光发射峰分别在380和435 nm.从聚合物1到聚合物3,薄膜的荧光发射最大半峰宽逐渐降低.大体积刚性吸电子2,4,6-三苯基-1,3,5-三嗪基团的引入,使聚合物1,2和3的热稳定性、蓝光发射的色纯度和光谱稳定性逐渐提高,不同工作电压驱动下聚合物3稳定的电致发光光谱进一步证明了这一点.聚合物1,2和3的最高占有轨道能级分别为-5.72,-5.95和-5.96eV,最低未占有轨道能级分别为-2.70,-2.39和-2.43 eV.聚合物1,2和3的三线态能级分别为2.82,2.81和2.97 eV.聚合物1,2和3的单线态-三线态能级差分别是0.32,0.32和0.15 eV.4-己氧基苯的引入使聚合物的能隙变宽,而吸电子的2,4,6-三苯基-1,3,5-三嗪的引入使聚合物单线态-三线态能级差依次减少.聚合物1,2和3粉末均易于形成非晶薄膜.聚合物3粉末的有序性介于聚合物1和2之间,聚合物2侧链的烷氧基苯有助于提高固体粉末有序形态的多样化.综合结果表明,侧链含有刚性4-己氧基苯和2,4,6-三苯基-1,3,5-三嗪基团的无规共聚物3具有更佳的综合光电性质.     

Narrow band gap D–A copolymer of indacenodithiophene and diketopyrrolopyrrole with deep HOMO level: Synthesis and application in field‐effect transistors and polymer solar cells

A novel fused ladder alternating D–A copolymer, PIDT–DPP, with alkyl substituted indacenodithiophene (IDT) as donor unit and diketopyrrolopyrrole (DPP) as acceptor unit, was designed and synthesized by Pd‐catalyzed Stille‐coupling method. The copolymer showed good solubility and film‐forming ability combining with good thermal stability. PIDT–DPP exhibited a broad absorption band from 350 to 900 nm with an absorption peak centered at 735 nm. The optical band gap determined from the onset of absorption of the polymer film was 1.37 eV. The highest occupied molecular orbital level of the polymer is as deep as ?5.32 eV. The solution‐processed organic field‐effect transistor (OFETs) was fabricated with bottom gate/top contact geometry. The highest FET hole mobility of PIDT–DPP reached 0.065 cm² V^?1 s^?1 with an on/off ratio of 4.6 × 10⁵. This mobility is one of the highest values for narrow band gap conjugated polymers. The power conversion efficiency of the polymer solar cell based on the polymer as donor was 1.76% with a high open circuit voltage of 0.88 V. To the best of our knowledge, this is the first report on the photovoltaic properties of alkyl substituted IDT‐based polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Relaxation of photo-excitations in films of oligo- and poly-(para-phenylene vinylene) derivatives

The photo-luminescence from solid films of poly(para-phenylene vinylene) polymers and an oligomeric model system, consisting of seven repeat units, are investigated at low temperature (8 K) using time-resolved spectroscopic techniques. Results are compared to those for the materials in solution. In the case of the oligomer, the shape of the visible absorption band observed for the film is quite different from the band shape for the polymer in frozen solution and is characteristic of H-type aggregates. Theoretical models are presented describing the dependence of the band shape of absorption and emission spectra on intermolecular excited state interactions, electron-vibration coupling and disorder represented by distributions of the molecular excitation and intermolecular interaction energies. Using these models, it is concluded that intermolecular interactions in the film of the oligomer are strong (1400 cm⁻¹), and the disorder low, implying delocalization of the excitation over several molecules. In accordance with these models the fluorescence lifetime for the film (2 ns) is considerably longer than for isolated molecules in solution (0.45 ns). The emission spectra of the film, taken early after excitation, are consistent with delocalization of the excitation over several molecules. A time-dependent red shift of the fluorescence band is observed and interpreted in terms of migration of localized excitations between disorder induced trap sites, which exist in the low energy tail of the density of excited states. For the polymers, differences between the shape of the absorption bands of solid film and frozen solution are smaller than for the oligomer indicating that interchain interactions that are, on average, weaker than for the oligomer. For the polymer films, a time-dependent red shift of the emission is observed and fluorescence depolarization measurements provide direct evidence for migration of the photo-excitations between trap sites. For one polymer, a time dependent change in the band shape of the fluorescence after pulsed excitation is observed with the band shape of the long-lived emission being compatible with that expected for an excitation delocalized over at least two, nearly parallel aligned, chains. For a second polymer, the emission band shape and its time evolution indicate that the major part of the fluorescence originates from disorder induced luminescent sites. These results indicate that the spectroscopic properties of films of π-conjugated polymer critically depend on parameters such as density of defects and excited state interchain interaction energy.     

Synthesis and Properties of Poly(4,8-dialkoxy-1,5-naphthalenevinylene)s

Novel conjugated materials, poly(4,8-dialkoxy-1,5-naphthalenevinylene)s (OC_n-PNV, n = 4, 6, 8, and 12), have been prepared by a method similar to the Gilch procedure. The structure, optical and thermal properties of these polymers with various alkoxy side chain lengths have been evaluated by IR, UV-Vis absorption, fluorescence emission and thermogravimetric analysis. The band gap of OC_n-PNV increases with increasing side chain length. Moreover, wavelengths of the photoluminescence (PL) emission peaks (λ_max) of OC_n-PNV solutions decrease with increasing alkoxy side chain length. This is probably due to the entanglement of long side chains that causes distortion of the conjugated main chains and thereby raises band gap of the polymer. PL λ_max's of these polymers in film state are red-shifted by 14–59 nm than those in solution state. The red-shift is due to the more chain aggregations after spin coating from solution into film state and consequently the lower band gap in the film state. Besides, the polymer with shorter side chains is more thermally stable than that with longer side chains.     

Thienopyrazine or dithiadiazatrindene containing low band gap conjugated polymers for polymer solar cells

Four new low-band-gap alternating copolymers （P-1, P-2, P-3 and P-4） based on electron-rich benzodithiophene and newly developed electron-deficient units, thienopyrazine or dithiadiazatrindene derivatives, were synthesized by Stille polycondensation. All polymers exhibit good solubility in common organic solvents and a broad absorption band in the visible to near-infrared regions. The film optical band gaps of the polymers are in the range of 1.28-2.07 eV and the highest occupied molecular orbital （HOMO） energy levels are in the range of-4.99 eV to -5.28 eV. Bulk heterojunction polymer solar cells （PSCs） of the polymers were fabricated with phenyl-C61-butyric acid methyl ester （PC61BM） as acceptor material, and a power conversion efficiency of 0.80% was realized with P-1 as donor material.     

Incorporating perylene moiety into poly(phenothiazine-co-bithiophene) backbone for higher charge transport

Low band gap pi-conjugated polymers composed of phenothiazine, bithiophene, and perylene moieties were prepared in high yields by using a palladium-catalyzed Suzuki coupling reaction. The polymers were characterized by NMR, gel permeation chromatography, and elemental analysis. The characterizations revealed that high-molecular weight (weight-average molecular weight up to 42,400 g/mol) polymers were thermally stable with a decomposition temperature in the region of 338-354 degrees C and their glass transition temperatures (Tg) ranging from 124 to 136 degrees C. All polymers demonstrated broad optical absorption in the region of 300-550 nm with efficient blue-green light emission. The absorption was broadened further (for ca. 50 nm) when the perylene moiety was incorporated. Cyclic voltammograms displayed that the p- and n-doping processes of all the polymers were partially reversible and that electrochemical band gaps were as low as -2.30 eV with the incorporation of a perylene moiety. The hole mobility of polymers was evaluated by using the space-charge-limited current model with a device structure of ITO/PEDOT:PSS/polymer/Ca. The results show that the incorporation of perylene is beneficial for improving the hole mobility of the conjugated polymers.     

Blue-luminescent poly(p-phenylenevinylene) derivatives: Synthesis and effect of side-group size on the optical properties

New conjugated polymers based on separated PPV-type chromophores and incorporating different types of solubilizing side-groups (ethoxy: P1, hexyloxy: P2, dodecyloxy: P3 and benzyloxy: P4) were synthesized via Wittig polycondensation, using a series of bisphenol A-derived di(triphenylphosphonium) salts as starting monomers. The polymers are soluble in common organic solvents and their structures were confirmed by ¹H NMR, ¹³C NMR and FTIR spectroscopies. The optical properties of these materials were investigated by UV–vis absorption and fluorescence spectroscopies. In dilute solution, quasi-identical fluorescence spectra were obtained and all the polymers showed a blue emission (420, 445 nm) and a narrow spectrum. In thin solid films, the polymers show side-group-dependent optical behavior and, whereas the emission remains blue in the case of P2, P3 and P4, a green fluorescence was observed for the ethoxylated polymer P1. From cyclic voltammetry analysis, the electrochemical band gaps were estimated to be 2.99, 3.07, 3.15 and 3.06 eV for P1, P2, P3 and P4, respectively. Single-layer diode devices of the [indium tin oxide/polymer/aluminum] configuration have been fabricated and show relatively low turn-on voltages between 2.6 and 4.9 V.     

Synthesis of phenanthro[1,10,9,8‐cdefg]carbazole‐based conjugated polymers for organic solar cell applications

Low bandgap polymers with dithienylquinoxaline moieties based on 6H‐phenanthro[1,10,9,8‐cdefg]carbazole were synthesized via the Suzuki coupling reaction. Alkoxy groups were substituted at two different positions on the phenyl groups of the quinoxaline units of these polymers: in the para‐position (PPQP) and in the meta‐position (PPQM). The two polymers showed similar physical properties: broad absorption in the range of 400–700 nm, optical bandgaps of ～1.8 eV, and the appropriate frontier orbital energy levels for efficient charge transfer/separation at polymer/PC₇₁BM interfaces. However, the PPQM solar cell achieved a higher PCE due to its higher J_sc. Our investigation of the morphologies of the polymer:PC₇₁BM blend films and theoretical calculations of the molecular conformations of the polymer chains showed that the polymer with the meta‐positioned alkoxy group has better miscibility with PC₇₁BM than the polymer with the para‐positioned alkoxy group because the dihedral angle of its phenyl group with respect to the quinoxaline unit is higher. This higher miscibility resulted in a polymer:PC₇₁BM blend film with a better morphology and thus in a higher PCE. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 796–803     

Small band gap conjugated polymers based on thiophene–thienopyrazine copolymers

In this study, five small band gap thiophene ( TH )–thienopyrazine ( TP ) conjugated copolymers were synthesized by Stille‐coupling reaction. The polymer structures consisted of one to four thiophene rings with the TP of different side groups provided a systematical investigation on the structure–electronic property relationship. The absorption maxima of the polymer films decreased from 850 to 590 nm as the thiophene moieties increased from thiophene to quaterthiophene. The optical and electrochemical band gaps of the studied poly[2,3‐didodecyl‐5‐(thiophen‐2‐yl)thieno[3,4‐b]pyrazine] ( PTHTP‐C12 ) were 0.97 and 0.78 eV, respectively, indicating a significant intramolecular charge transfer. The theoretical geometry and electronic properties of the TH ‐ TP copolymers by the density functional theory at the B3LYP level and 6‐31G(d) basis set suggested that the bond length alternation enlarged with enhancing the thiophene content and resulted in the variation on the polymer band gap. The relatively small theoretical effective mass of poly( TH ‐alt‐ TP ) also indicated its potential applications for field transistor applications. Our study demonstrates the tunable electronic properties of small band gap copolymers by the thiophene content and the resulted geometry variation. Such polymers could be potentially used for near‐infrared electronic and optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5872–5883, 2007     

Synthesis,characterization, and electroluminescence of fluorene and carbazole‐based blue light‐emitting polymers with different noncoplanar molecular architectures

In order to investigate the explicit optoelectronic variations of the photoluminescent polymer with sterically hindered side chains, three novel alternate polymers (P0, P1, and P2) based on fluorene and carbazole moieties were successfully synthesized through Suzuki coupling reaction. The molecular structures of the polymers were fully characterized by ¹H‐NMR, ¹³C‐NMR, elemental analysis, and gel permeation chromatograph, respectively. The photophysical properties, thermal stability, and energy band gaps of polymers P0, P1, and P2 were further examined through UV–vis absorption, photoluminescent spectra, differential scanning calorimetry, thermogravimetric analysis, and cyclic voltammetry. The experimental results indicated that the polymers took on wide band gaps of about 3.50 eV with deep blue emission in thin solid films. These polymers were found to show a high thermal stability with decomposition temperatures at 5% weight loss of the compounds in the range of 353–416 °C. Blue light‐emitting electroluminescent devices of the most branched polymer P2 with highest light‐emitting efficiency as emitting layers were characterized, which showed obviously improved spectral stabilities with respect to the parent polyfluorene materials. In conclusion, we have established an effective method to improve the spectral stabilities of polyfluorene material by synthesizing the zigzag‐shaped copolymer of fluorene and carbazole with sterically hindered pendant moieties of different molecular sizes. Copyright © 2014 John Wiley & Sons, Ltd.     

Multipurpose selenophene containing conjugated polymers for optoelectronic applications

In this study, two new conjugated polymers were synthesized including benzotriazole (BTz) as the acceptor unit and selenophene as the π bridge donor segment. These acceptors were coupled with fluorene and carbazole via Suzuki condensation reactions. Electrochemical band gaps were calculated as 2.45 eV for P1 and 2.40 eV for P2. Electrochemical and optical studies of polymers indicate that both polymers are promising candidates for organic solar cell (OSC) and polymer organic light emitting diode (PLED) applications since they have suitable HOMO-LUMO energy levels and appropriate absorption and emission band ranges. Light emitting properties of synthesized polymers were investigated and the highest luminance value was found as 6608cd/m² for P1 at 8 V. Photovoltaic properties of polymers were investigated and the optimized device based on P2 showed 1.75% power conversion efficiency for P2 under AM 1.5 G illumination at 100 mW/cm².     

Synthesis of polymers containing 1,2,4‐oxadiazole as an electron‐acceptor moiety in their main chain and their solar cell applications

To explore the aptitude of 1,2,4‐oxadiazole‐based electron‐acceptor unit in polymer solar cell applications, we prepared four new polymers (P1–P4) containing 1,2,4‐oxadiazole moiety in their main chain and applied them to solar cell applications. Thermal, optical, and electrochemical properties of the polymers were studied using thermogravimetric, absorption, and cyclic voltammetry analysis, respectively. All four polymers showed high thermal stability (5% degradation temperature over 335 °C), and the optical band gaps were calculated to be 2.20, 1.72, 1.37, and 1.74 eV, respectively, from the onset wavelength of the film‐state absorption band. The energy levels of the polymers were found to be suitable for bulk heterojunction (BHJ) solar cell applications. The BHJ solar cells were prepared by using the synthesized polymers as a donor and PC₇₁BM as an electron acceptor with the configuration of ITO/PEDOT:PSS/polymer:PC₇₁BM (1:3 wt %)/LiF/Al. One of the polymers was found to show the maximum power conversion efficiency of 1.33% with a Jsc of 4.95 mA/cm², a V_oc of 0.68 V, and a FF of 40%, measured using AM 1.5 G solar simulator at 100 mW/cm₂ light illumination. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Alternating fluorene copolymers containing isothianaphthene derivatives: A study of their aggregation properties and small band gap

Several fluorene copolymers containing isothianaphthene units ( P1 , P2 , and P3 ) or similar derivatives ( P4 and P5 ) have been synthesized by Pd‐catalyzed Suzuki polymerization. The monomers containing isothianaphthene were prepared by a ring‐closure reaction with Lawesson's reagent. Strong photoluminescence (PL) quenching in the film state was observed for P1 and P2 , which was mainly due to the enhanced quinoid character formed by introducing the isothianaphthene unit. Their energy levels of the compounds were determined using cyclic voltammetry. Among the polymers tested, the polymer containing both an isothianaphthene and a selenophene unit, P2 , showed the smallest band gap of 1.85 eV. The influence of structural variation on the band gap of the polymer chains was further investigated by optimizing the geometries of several model monomers. Our results based on the optical and electrochemical properties combined with theoretical calculations showed that polymers containing isothianaphthene have small band gaps, rigid conformations, and strong tendencies to aggregation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3573–3590, 2008     

Low‐Band‐Gap BODIPY Conjugated Copolymers for Sensing Volatile Organic Compounds

Conjugated polymers with strong photophysical properties are used in many applications. A homopolymer ( P1 ) and five new low band gap copolymers based on 4,4′‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) and acceptors 3,6‐dithienyldiketopyrrolopyrrole ( P2 ), phthalimide ( P3 ), benzotriazole ( P4 ), 4,7‐dithienyl[1,2,3]triazolo[4,5g]quinoxaline ( P5 ), and 2,5‐dithienylthieno[3,4‐b]pyrazine ( P6 ) were prepared by means of Sonogashira polymerization. The characterization of polymers by using ¹H NMR, absorption, and emission spectroscopy is discussed. All polymers with high molecular weights (M_n) of 16 000 to 89 000 g mol^?1 showed absorption maxima in the deep‐red region (λ=630–760 nm) in solution and exhibited significant redshifts (up to 70 nm) in thin films. Polymers P2 , P5 , and P6 showed narrow optical band gaps of 1.38, 1.35, and 1.38 eV, respectively, which are significantly lower than that of P1 (1.63 eV). The HOMO and LUMO energy levels of the polymers were calculated by using cyclic voltammetry measurements. The LUMO energy levels of BODIPY‐based alternating copolymers were independent of the acceptors; this suggests that the major factor that tunes the LUMO energy levels of the polymers could be the BODIPY core. All polymers showed selective and reproducible detection of volatile organic solvents, such as toluene and benzene, which could be used for developing sensors.     

Cn films (n=50, 52, 54, 56, and 58) on graphite: cage size dependent electronic properties

Novel semiconducting materials have been prepared under ultrahigh-vacuum conditions by soft-landing mass-selected Cn+ (50< or =n<60; even n) on highly oriented pyrolytic graphite surfaces at mean kinetic energies of 6 eV. In all cases, Cn films grow according to the Volmer-Weber mechanism: the surface is initially decorated by two-dimensional fractal islands, which in later deposition stages become three-dimensional dendritic mounds. We infer that Cn aggregation is governed by reactive sites comprising adjacent pentagons (or heptagons) on individual cages. The resulting covalent cage-cage bonds are responsible for the unusually high thermal stability of the films compared to solid C60. The apparent activation energies for intact Cn sublimation range from 2.2 eV for C58 to 2.6 eV for C50 as derived from thermal desorption spectra. All Cn films exhibit a common valence-band ultraviolet photoelectron spectroscopy spectral feature located around the center of a broad highest occupied molecular-orbital (HOMO)-derived band (EB approximately 2.5 eV). This feature has been assigned to Cn units covalently linked to each other in polymeric structures. To within experimental accuracy, the same work function (4.8 eV) was determined for thick films of all Cn studied. In contrast, "HOMO" ionization potentials were cage size dependent and significantly lower than that obtained for C60. C58 exhibited the lowest HOMO (6.5 eV). Band gaps of Cn films have been determined by depositing small amounts of Cs atoms onto the topmost film layer. HOMO-lowest unoccupied molecular-orbital-derived band gaps between 0.8 eV (C52) and 1.8 eV (C50) were observed, compared to 1.5 eV for solid C60.     

Electrical, optical, thermoelectric power, and dielectrical properties of organic semiconductor poly(1,12-bis(carbazolyl) dodecane) film

Electrical conductivity, optical, thermoelectric, and dielectrical properties of the poly(1,12-bis(carbazolyl) dodecane) film have been investigated. The activation energy for electrical conductivity and room-temperature electrical conductivity (at 25 degrees C) values were found to be 0.25 eV and 2.65 x 10-6 S/cm, respectively. The thermoelectric power results suggest that the conductivity is due to large polarons (i.e., the carriers in polymer move by hopping in the localized states at band gap edges). Electrical conductivity and thermoelectric power results confirm that the polymer is a p-type organic semiconductor. Optical absorption results suggest that the direct allowed transitions are dominant in the fundamental absorption edge in the polymer with optical band gap value of 2.72 eV. The refractive index dispersion of the polymer obeys the single oscillator model with oscillator energy (Eo = 3.06 eV) and dispersion energy (Ed = 17.82 eV) values. Alternating current conductivity results suggest that the hopping conductivity is dominant in the polymer. The dielectrical properties exhibit a non-Debye relaxation.     

A spectroelectrochemical study on single-oscillator model and optical constants of sulfonated polyaniline film

The optical properties of sulfonated polyaniline (SPAN) thin film prepared by electrochemical method have been investigated. Polychromic behavior of SPAN thin film (transparent yellow-green-dark blue) was observed when the cyclic voltammograms were taken between -0.25 V and +1.90 V (vs. Ag/AgCl, sat.) during the growth of polyaniline film. In situ UV-vis spectra of the polymers-indium tin oxide (ITO) glass electrode were taken during the oxidation of the polymers at different applied potentials. The direct band gap values of SPAN thin film changed from 3.771 eV to 3.874 eV with the applied potentials. From in situ UV-vis spectra, the optical constants such as refractive index and dielectric constant of the SPAN thin film were determined. The important changes in absorption edge, refractive index and the dielectric constant were observed due to the applied potentials. The refractive index dispersion curves of the film obey the single-oscillator model and oscillator parameters changed with the applied potentials. The most significant result of the present work is in situ spectroelectrochemical method, which can be used to modify the optical band gaps and constants.