Search

The article focuses on the electrochemical and optical properties of n-type conjugated polymers, containing naphthalene diimide (NDI) acceptor units in their neutral and reduced states. Cyclic voltammetry reveals significant differences between the electrochemical stability of NDI-based polymers in the first and second reduced states. Combined electrochemical, spectral and conductivity results show that the first reduced state is related to the formation of radical anions delocalised on NDI units, with formation of interchain π-stacks between adjacent reduced NDI units being probable. The second reduced state is related to the formation of spinless species, whose properties are modified to a greater extent by the donor units. These results indicate that n-doping of naphthyl diimide-based conjugated polymers is significantly different from the doping of typical p-type conjugated polymers, which entails the formation of delocalised charge carriers, such as polarons and bipolarons. The n-type (electron acceptor) performance of NDI-based polymers was practically verified by employing them, along with poly(3-hexylthiophene) electron donor, in bulk heterojunction photovoltaic devices.

The synthesis and characterization of a family of indene-C60 adducts obtained via Diels–Alder cycloaddition [4 + 2] are reported. The new C60 derivatives include indenes with a variety of functional groups. These adducts show lowest unoccupied molecular orbital energy levels to be at the right position to consider these compounds as electron-transporting materials for planar heterojunction perovskite solar cells. Selected derivatives were applied into inverted (p–i–n configuration) perovskite device architectures, fabricated on flexible polymer substrates, with large active areas (1 cm2). The highest power conversion efficiency, reaching 13.61%, was obtained for the 6′-acetamido-1′,4′-dihydro-naphtho[2′,3′:1,2][5,6]fullerene-C60 (NHAc-ICMA). Spectroscopic characterization was applied to visualize possible passivation effects of the perovskite’s surface induced by these adducts.

The first comprehensive spectroelectrochemical account of the behaviour of regioregular (RR-P3HT) and statistical (ST-P3HT) poly(3-hexylthiophenes) in solution is presented, in contrast to the many reports dealing with P3HT films merely deposited from solution. The conducted experiments revealed that the two types of P3HTs behave in sharply different ways upon the application of electrochemical stimuli: ST-P3HT readily precipitates at mildly oxidative potentials, while the precipitation of the RR-P3HT takes place to a much lesser extent, even at higher potentials. The two polymers, studied via UV–Vis–NIR–EPR spectroelectrochemistry, exhibited properties mostly in line with earlier reports. Further study revealed that RR-P3HT largely remains in solution, even in its doped form, whereas only traces of the doped ST-P3HT are observed in solution in identical conditions. The high concentration of the doped RR-P3HT in solution can be explained by its ability to form soluble polymer agglomerates, in which the positive charge of the p-doped chains is stabilised by and delocalised over neighbouring, interacting undoped chains. These conclusions are consistent with SEM micrographs, which show that after cycling the potential of the electrode in a solution of ST-P3HT, a uniform layer is formed, covering most of the surface of the electrode, whereas in the case of RR-P3HT surface coverage is marginal and formed layer has the appearance of veined blotches. Graphical abstract

First report of π-conjugated push-pull copolymer systems with 4,4′-bipyridine moieties in the main macromolecular chain is presented. C-substitution pattern of electropolymerisable bithiophene pendants at the 4,4′-bipyridine unit offered the versatility to retain the latter as free amine, or convert it into bipyridylium salt. Both structures have been prepared and investigated, delivering the first example of a polymer with viologen unit making up the extended π-bond. Detailed electrochemical, spectroelectrochemical and quantum chemical study of these new polymer systems and their 2,2′-bipyridine analogues has shown that while linear structure and extended conjugation in the latter help it to accommodate charge carriers characteristic for heavily doped polythiophene, the conjugation break afforded by the meta substitution pattern across the 4,4′-pirydyl unit makes the polymer behave like an ensemble of shorter oligomeric segments with better defined electron transitions and sharper, and faster electrochromic response. Effective π-π interchain coupling between α,ω-bis(2-pyridyl)quaterthiophene repeating units was observed, whereas intramolecular interactions were found to dominate in the linear 2,2′-bipyridyl based polymer. While the bithiophene derivative of methyl viologen electropolymerised less easily than its corresponding non-quaternised derivative, the resulting polymer films demonstrated decent stability when subject to subsequent p- and n-doping, featuring pronounced charge trapping/detrapping signatures. Furthermore, ion pairing between the viologen and weakly basic PF 6 − and CF 3 SO 3 − counterions has been found to impact the redox chemistry of bithiophene functionalised viologen structure. Experimental findings have been confronted with results of quantum chemical computations helping to elucidate the electrochemical and spectroelectrochemical observations made. Presented study delivers insights into the doping processes taking place in conjugation disrupted 4,4'-bipyridine core copolymers, helping to evaluate their potential as substrates for new tuneable π-conjugated polymeric systems.

1,3,4-Thiadiazole, 2,2'-bi(1,3,4-thiadiazole), 2,2':5',2″-ter(1,3,4-thiadiazole), and 2,2':5',2″:5″,2‴-quater(1,3,4-thiadiazole) symmetrically disubstituted with 3-alkyl-(2,2'-bithiophen)-5-yl were synthesized by new procedures using readily available ethyl 3-alkyl-(2,2'-bithiophene)-5-carboxylate as a convenient substrate. These new compounds with a fixed number of donor rings and increasing number of acceptor rings showed very interesting, tunable redox properties. In particular, they exhibited electron affinities (EAs) ranging from -3.06 to -3.83 eV, reaching EA values desired for air-operating n-type organic semiconductors. Their electrochemically determined ionization potentials were only moderately dependent on the number of thiadiazole rings, varying from 5.83 to 6.01 eV. Emission spectra of these compounds could also be tuned in a wide range (from 470 to 600 nm). Spectroscopic and electrochemical data were confirmed by density functional theory calculations demonstrating full consistency.

A structure-property study across a series of donor-acceptor-donor structures composed of mono- and bi-(1,3,4-oxadiazole) units symmetrically substituted with alkyl functionalized bi-, ter- and quaterthiophene segments is presented. Synthetically tailoring the ratio of electron-withdrawing 1,3,4-oxadiazole to electron-releasing thiophene units and their alkyl grafting pattern permitted us to scrutinize the impact of these structural factors on the redox, absorptive and emissive properties of these push-pull molecules. Contrasting trends of redox potentials were observed, with the oxidation potential closely following the donor-to-acceptor ratio, whereas the reduction potential being tuned independently by either the number of acceptor units or the conjugation length of the donor-acceptor system. Increasing the thiophene unit contribution delivered a shift from blue to green luminescence, while the structural rigidity afforded by intramolecular non-covalent interactions between 1,3,4-oxadiazole and the thiophene moieties has been identified as the prime factor determining the emission efficiency of these molecules. All six structures investigated electro-polymerize easily, yielding electroactive and electrochromic polymers. The polymer doping process is largely influenced by the length of the oligothiophene repeating unit and the alkyl chain grafting density. Polymers with relatively short oligothiophene segments are able to support polarons and polaron-pairs, whereas those with segments longer than six thiophene units could also stabilize diamagnetic charge carries - bipolarons. Increasing the alkyl chain grafting density improved the reversibility and broadened the working potential window of the p-doping process. Stable radical anions have also been investigated, bringing detailed information about the conjugation pattern of these electron-surplus species. This study delivers interesting clues towards the conscious structural design of bespoke frontier energy level oligothiophene functional materials and their polymers by incorporating a structurally matching 1,3,4-oxadiazole unit.

The effect of oxygen conditioning on the performance of polyaniline (PANI) membranes is presented and discussed. The presence of the conditioning effect in such kind of polymer matrix was confirmed by measuring a variation in spin concentration using electron paramagnetic resonance (EPR) spectroscopy. The observed decrease in spin concentration indicates the presence of the dissolved oxygen incompletely removed from PANI matrix. After the prolonged contact between oxygen and PANI membrane, a pronounced decrease in membrane’s selectivity was observed, which may be explained by the firm and permanent interaction between oxygen molecules and nitrogen paramagnetic centers of PANI and could be considered as a kind of PANI irreversible doping process.

In the rapidly developing field of conjugated polymer science, the attribute of electrochromism these materials exhibit provides for a multitude of innovative application opportunities. Featuring low electric potential driven colour change, complemented by favourable mechanical and processing properties, an array of non-emissive electrochromic device (ECD) applications lays open ahead of them. Building up from the simplest two-colour cell, multielectrochromic arrangements are being devised, taking advantage of new electrochromic materials emerging at a fast pace. The ultimate device goal encompasses full control over the intensity and spectrum of passing light, including the two extremes of complete and null transmittance. With numerous electrochromic device architectures being explored and their operating parameters constantly ameliorated to pursue this target, a summary and overview of developments in the field is presented. Discussing the attributes of reported electrochromic systems, key research points and challenges are identified, providing an outlook for this exciting topic of polymer material science.

Synthesis, spectral and electrochemical properties of a series of new panchromatic BODIPY donor–acceptor–donor derivatives, comprising carbazole conjugated with systematically elongated framework by thiophene – based linkers were investigated. It has been found that elongation of the π-system with one thiophene unit shifts the spectra toward near infrared, while incorporation of next thiophene derivatives has only limited influence on the lowest energy transition, causing no further shift of absorption maxima. Elongation of π-conjugation of the donor arm tunes the electron properties, influencing the ionization potential (IP) and electron affinity (EA) values of the molecules. The experimental results are supported by quantum chemical computations revealing that electron density of SOMO orbital is low at the 3-positions of terminal carbazole units in BODIPY push–pull oligomers while elongating their backbone, thus preventing them to undergo electrochemical polymerization giving reversibly p- and n-dopable products. Presented study tests the influence and limitations of incorporation of electron – rich substituents for designing panchromatic BODIPY systems.

Five and six heterocycle ring assemblies, comprising triazole or oxadiazole acceptor (A) units and thiophene or alkylthiophene donor (D) units in a DDADD and DDAADD arrangement, have been synthesised and characterised by spectroscopic and electrochemical means. It is demonstrated that the replacement of a weaker acceptor (triazole) by a stronger one (oxadiazole) in DDADD compounds results in lowering of the frontier molecular energy gap by 70 meV from 2.94 to 2.87 eV. For oxadiazole-centred compounds these gaps can be further lowered by increasing the number of A units and alkyl solubilising substituents, down to 2.76 eV for the DDAADD compound containing four alkyl pendants. The photoluminescence quantum yield exceeds 50 % for DDADD compounds and reaches 78 % for DDAADD ones. All compounds, when dispersed in a blend consisting of 70 % poly(vinylcarbazole) (PVK) and 30 % of 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) (host–guest configuration), demonstrate light-emitting diode behaviour, affording blue, tuneable emission with luminances reaching 120 cd m−2 and luminous efficiencies of 0.12 cd A−1 for non-optimised devices.

N-Protected 4-(anilinomethyl)thiophene-2-carbaldehydes were prepared by the reaction of easily available 4-chloromethylthiophene-2-carbaldehyde with N-(2-halogenophenyl) substituted acetamides, 4-methylbenzenesulfonamides and carbamates in the presence of K2CO3 or Cs2CO3. The compounds obtained were converted to 4,5-dihydrothieno [3,2-c]quinoline-2-carbaldehydes by palladium catalyzed intramolecular cyclization in homogenous or heterogenous (Pd/C) conditions with good yields and subsequently used for preparing of 2-functionally substituted thieno [3,2-c]quinoline derivatives (nitriles, carboxamides, carboxylic acids, esters). The optical properties of 2-functionally substituted thieno[3,2-c]quinolines and 4H-thieno[3,2-c]chromenes have been studied. Moderate to high fluorescence quantum yields are observed for these compounds ranging from 0.15 to 0.87. Structure - optical properties relationships have been established for the compounds synthesized, and their prospective application as invisible ink dyes was practically demonstrated.

The influence of different thiophene donor units on electrochemical and spectroscopic properties of benzothiadiazole based donor–acceptor π-conjugated organic materials is studied. Two different structure modification vectors of the donor units are being considered – one addressing the intermolecular interactions through off-conjugation side chain architecture, and the other focusing on intramolecular interactions tuned by in-conjugation substituents. Electrochemical and simultaneous in situ EPR-UV-Vis-NIR spectroelectrochemical studies of the oxidative (p-) and reductive (n-) doping processes, which are responsible for the optoelectronic properties of these materials, revealed their disparate course and dissimilar effects of redox reactions of the conjugated π-bond. While p-doping prevalent species were found to comprise intensively interacting spin bearing and spinless charge carriers, the n-doping state was found to involve only one type of negatively charged carrier, with spin carrying species being selectively generated at due cathodic potentials. No spin pairing of these negative polarons was observed with their increasing population behaving like a collection of localised charge carriers. Qualitative and quantitative comparisons between the p- and n-doping carrier populations provided independent support for the spin pairing phenomena of positive charge carriers. Steric effects of varying alkyl side chain substitution have demonstrated predominant impact on the electrochemical properties of investigated polymers, and, thereto related, stability of n-doped state, while mesomeric effects of different 3,4-ethylenechalcogenide thiophene functionalities have been found to shape the energy level related spectral properties of these polymers, with particular reference to p-doping induced charged states. These findings provide new insights into the factors requiring attention during structure tailoring of donor–acceptor assemblies for organic optoelectronic applications.

Electrochemical and spectroelectrochemical properties of a series of new penta-ring donor–acceptor compounds, comprising 1,3,4-oxadiazole, 1,3,4-thiadiazole, and 1,2,4-triazole central ring, symmetrically connected to substituted bithiophenes, were investigated. Aromaticity and electrophilic–nucleophilic traits of the aza-heterocyclic units, fostering inductive and resonance effects that translate to conjugation enhancement and electron (de)localization, were found a major factor determining the key electron properties of ionization potential (IP) and electron affinity (EA) of these molecules. Replacing the alkyl thiophene substituent for an alkoxy one afforded certain control over the two parameters as well. All studied compounds were found to undergo electrochemical polymerization giving p- and n-dopable products, featuring good electrochemical reversibility of their oxidative doping process, as demonstrated by cyclic voltammetry and UV–vis–NIR, EPR spectroelectrochemistry. While electropolymerization o...

Mono- and disubstituted EHBG (HBED) ligands of different kind: forming hydrogen bonds ( p -OMe, p -NHAc) and of high lipophilicity (3,4-Me 2 , p -Ph) were obtained. The ligands were complexed with Fe(III). Complexes so obtained were studied for their stability in different pH environments; and r 1 relaxivity, which turned out the highest for Fe-EHBG-NHAc, i.e. 0.95 mM −1 s −1 in aqueous solution and 1.34 mM −1 s −1 for Fe-EHBG-Me 2 in bovine serum. EPR signals were observed at g -factor of 4.27 indicative of Kramer's doublet transitions of a rhombically distorted high-spin paramagnetic center.

The redox processes accompanying electrochemical oxidation of 1,3,5-tris(bithiophene)benzene (6TPh) and its products have been investigated using a suite of spectroelectrochemical tools. Investigated tri-functional molecule, featuring reactive bithiophene units can be considered a model of numerous star shaped compounds – the building blocks of dense π-conjugated polymer networks. Accounting for conjugation disruption between the meta-arranged bithiophene groups, it is found that electrochromic films generated upon 6TPh electrooxidation comprise primarily dimers (6TPh)2, whose α,ω-diphenylquaterthiophene units are the principal redox doping active species. Upon reaching a certain, electrochemically inconspicuous oxidation threshold, profound changes take place in the oligomer film, incurring irreversible changes to its electroactive properties, previously observed for these systems. An attempt is made to examine the nature of these changes and the impact they have on the doping behaviour of this intriguing π-conjugated system.

Thin films of poly(3-dodecylpyrrole) have been found to yield multi-electrochromic characteristics. Optimisation of the polymer electrodeposition process enabled fabrication of layers exhibiting three distinct colourations at different oxidation levels. Coupled EPR-UV-Vis-NIR spectroelectrochemistry enabled correlation of these colour changes with the formation and decay of polaron and bipolaron charge carriers, offering an insight into the mechanism of doping/dedoping processes taking place in this polymer. The ionisation potential of the polymer was found to be very low, with valence band edge located at -3.7 eV, explaining the relative oxidation ease of the polymer and accounting for an ample number of spins present in the electrochemically dedoped polymer film. Maximum optical contrast of up to 15% and a visible light range averaged one of 10% was observed. Dynamic colour switching contrast of 10% is attainable at 5 s switching time, while switching steps as short as 0.5 s afford 6% contrast value. The fully oxidised polymer features broad UV-Vis absorption, making the system an interesting candidate for transmissive-to-black electrochromic devices.

Here we report the preparation of 3,6- bis(bithenyl)-N-decylcarbazole with low oxidation potential due to extended conjugation that underwent facile electrochemical polymerization to form stable electroactive polymer. We extended the conjugation of the monomers in comparison to the carbazole and large decrease were observed in the oxidation potential at which polymerization occurs. To lower the oxidation potential of the monomer and control the optical and electronic properties of the polycarbazole, we attached the thiophene, bithiophene and 3,4-ethylenedioxythiophene (EDOT) at both the 3 and 6 positions of N-substituted carbazole. The monomers and their polymers were compared through electron paramagnetic resonance (EPR) and UV-Vis-NIR spectroelectrochemistry resulting in interesting properties. As optically active materials the CIE L*a*b chromaticity and other optical properties were observed.

Electrochemical polymerisation of 3-octylthiophene and 4,4′-dioctyl-2,2′-bithiophene in acetonitrile is reported. The nature of the resultant films was investigated through electrochemical and spectroelectrochemical means, in concert with quantum mechanical calculations to evidence the oligomeric nature of the deposits. Control of conjugation length through solubility modification is demonstrated through investigation of UV–vis spectra of polymers prepared in different solvents. ESR–UV–vis–NIR spectroelectrochemical measurements were used to gauge the differences in the behaviour of regioregular and regiorandom deposits. Conjugation length was found to vary significantly between the two polymers. This is shown to influence the nature of charge carriers generated upon p-doping of the system.

Polymer films of poly(3,4-ethylenedithiothiophene) obtained by electrochemical oxidative polymerisation of the corresponding monomer have been investigated. p-Doping process of the polymer was characterized by in situ EPR spectroelectrochemisty. Compared to its close relative – PEDOT, the polymer features two distinct voltammetric peaks. The results of our studies indicate that both represent faradaic processes and that each manifests generation of charge carriers in the polymer.

The π-electron delocalisation in conjugated thienylenevinylenes bearing arylethenyl chromophores, makes those materials interesting candidates for electro-optic applications. In this study, we report the results of electrochemical and UV–Vis/ESR spectroelectrochemical studies of a pair of thienylenevinylenes substituted by the 4-cyanostyryl group, bearing either a hydrogen, or methyl group terminated α carbons at the peripheral thiophene rings. The reactivity of various functional segments of investigated molecules was assessed by comparing the reactivity of the protected and unprotected counterparts and the behaviour of their electrooxidation products. For the capped derivative, two irreversible anodic redox processes giving electrochemically inactive products were observed, while the uncapped molecule yields electroactive materials already upon its first oxidation step.

A type of graft copolymer based on polysiloxane and regioregular poly(3-hexylthiophene) (P3HT) has been synthesised and its properties have been studied alongside those of its parent conjugated polymer&mdash, regioregular P3HT. Electrochemical analysis has revealed more significant changes in conformation of the copolymer film than was observed for P3HT. UV-Vis-NIR spectroelectrochemical investigation provided evidence of improved doping reversibility of the copolymer, despite its marginally increased band gap, as also confirmed by electroconductometric analysis. Evidence has been shown, indicating that polaron mobilities in both P3HT and the copolymer are higher than those of bipolaronic charge carriers, even though both systems exhibit standard doping/dedoping patterns. The grafted copolymer was tested in bulk heterojunction solar cells. Preliminary studies show a great potential of these polymers for application in photovoltaics. Power conversion efficiency of up to 2.46% was achieved despite the dilution of the P3HT chains in the copolymer.

Electrochemically synthesised polymers of long, 2-oxaalkyl chain derivatives of 3,4-ethylenedioxythiophene (EDOT) have been studied using in situ EPR spectroelectrochemistry. Originally developed as promising candidates for preparation of soluble PEDOT derivatives, their polymers themselves reveal interesting spectroelectrochemical properties, in some cases even superior to their family's parent. Our results indicate notable differences in potential dependencies of concentration of spins and Δ B pp width between the two polymers, indicating a major influence of the alkyl side chain length on specific properties of paramagnetic charge carriers appearing in these polymers in the course of their redox processes. Certain features of their spectroscopic response however, like the hysteresis of potential dependence of concentration of spins and Δ B pp widths, point to similarities of their doping - dedoping mechanism with the one of PEDOT.

Quantitative in-situ EPR spectroelectrochemical studies of poly(3,4-ethylenedioxythiophene) (PEDOT) have been carried out with an aim to gain new insights into the doping processes taking place in this polymer. Corroborating the findings made during previous studies of this polymer, absolute measurements conducted in this study provided new detailed information regarding some of the basic parameters characterising the doping process of this conjugated polymer. It was found that concentrations of paramagnetic centres in PEDOT vary from 0.02 spin per mer in the dedoped state up to a maximum of 0.12 spin per mer at 0.15 [e−/mer] doping level, corresponding to 1 spin per ca. 8.5 meric units. Such notable concentration values indicate that polarons represent a numerous charge carrier group in PEDOT, contrary to observations made for other members of polythiophene family. Furthermore polarons do not disappear at high doping levels of PEDOT but rather decrease their numbers gradually down to 0.08 spins per mer at a maximum doping level of 0.55 [e−/mer] attained in this study. Based on information about concentrations of spins and polymer doping charges, concentrations of bipolarons have been evaluated as a function of doping level. Results indicate that bipolaron formation starts at ca. 0.06 [e−/mer] doping level when spin generation efficiency begins to deviate from 1 and interspin interactions emerge as evidenced by doping level dependency of EPR signal linewidth (ΔBpp). Decomposition of complex EPR spectra of PEDOT in its doped state corroborated the presence of two groups of paramagnetic centres in this polymer. Based upon doping level dependencies of their spectroscopic parameters (concentration, ΔBpp linewidth and g-factor), the identity of these centres has been redefined compared to our previous reports, linking their properties with the type of polymer phase (crystalline or amorphous) they reside in.

Electrochemically synthesised polymers of ω-bromine 2-oxaalkyl derivatives of 3,4-ethylenedioxythiophene (EDOT) have been studied using in-situ ESR spectroelectrochemistry. While these compounds are versatile intermediates en route to EDOT derivatives bearing special functional groups, their polymers themselves show interesting properties. Results indicate differences in potential dependencies of concentration of spins, ΔB PP width and g-factor between the two polymers, indicating an influence of the alkyl side chain length on specific properties of paramagnetic charge carriers appearing in these polymers in the course of their redox processes. Compared to their parent polymer-PEDOT, some similarities in the behaviour of charge carries may be observed notably the hysteresis of potential dependence of concentration of spins and ΔB PP width, indicating that the doping-dedoping mechanism of these polymers may resemble the one in PEDOT.

Electrochemical doping and dedoping processes in poly(3,4-ethylenedioxythiophene)—PEDOT have been studied by in situ ESR spectroelectrochemistry with an aim to investigate the behaviour of charge carrying species, generated and annihilated in these processes, with changing potential. As an extension of earlier studies, we investigated the behaviour of PEDOT at high oxidation potentials, beyond the limit of electrochemical stability of the polymer located at ca. 1.6 V. Past this limit, a sudden and irreversible drop in the concentration of spins together with narrowing of the ESR signal is observed. Changes in the spectroscopic response of the film are irreversible as evidenced by the course of the subsequent reduction process, which by no means resembles the reduction process of the polymer recorded within the potential window in which the polymer is stable. Supplemented by results of electrochemical studies, it is concluded that direct overoxidation of the polymer chain most probably leads to a decrease in the conjugation length of the polymer's delocalised π-bond, through cross-linking of the polymer chains. Consequently, the remaining spins become trapped in isolated packets where they behave more like oligomer type radicals.

In situ ESR spectroelectrochemical studies of poly(3,4-butylenedioxythiophene) (PBuDOT) have been performed, in order to investigate more closely the species responsible for the conductivity of this polymer in the doped state. In the process of electrochemical doping of the polymer, ESR spectra at progressively changed potentials were recorded. Then the subsequent dedoping process was studied accordingly. The results reveal that PBuDOT’s ESR spectroscopic properties are markedly different form its close relative, poly(3,4-etylenedioxythiophene) (PEDOT). Firstly, the potential dependence of the spin concentration displays a clear peak-shaped transient with a gradual decrease at higher oxidation potentials. Similar behaviour is seen for the ΔB pp widths of the ESR signal, indicating that the type of interactions between paramagnetic centres is potential sensitive. The course of the reduction process of the polymer is more or less the reverse of the oxidation one, with only a slight hysteresis of the spin concentration and a barely discernible one of ΔB pp widths being observed. In PBuDOT, as in PEDOT, distinct narrow ESR lines revealing a noteworthy spin concentration in the reduced state of the polymer have also been observed. The presence of these residual spins in the dedoped polymer may indicate that the dedoping process of this polymer is indeed a slow one. The presence of trace amounts of impurities or oxygen may hinder the dedoping process, especially for thicker films.

Polymer support such as polypyrrole was selected as a matrix for heteropolyacid H 5 PMo 10 V 2 O 40 in an attempt to prepare heterogeneous catalysts containing two different active centers: protons and transition metal ions. Exchanging protons from heteropolyanions dispersed in polymer matrix into ferric or ferrous ions cause the modifications of their catalytic properties. It is manifested by decrease of activity of acid-base centers and increase of activity of oxidative-reductive centers. Oxidation state of iron in all samples before and after catalytic reaction is the same (Fe(III)), but their structure is not similar. For catalysts doped with ferric ions the structural order is much more pronounced than for these doped with ferrous ions.

Electrochemical studies of a series of regioregular 3-octylthiophene oligomers with 5–8 thiophene rings, chlorine end-capped at one α terminal position, have been conducted in solution and in thin film state. Results indicate gradual coalescing of the oxidation potentials of neutral and radical cation oligomer molecule, indicative of coming close to sufficient length of the molecule to allow for two separate radical cations to exist along its chain. With increasing number of thiophene rings in the molecule, further quasi-reversible oxidation reactions upon which trication and tetracation were formed have been observed at ever decreasing potentials. It was also observed that the oxidation of radical cations comes about more easily than that of electron-paired cations, the latter process being strongly dependent on the length of oligothiophene chain. Thin film electrochemistry revealed that the processes taking place during redox reactions differ from those in solution. Sharp oxidation peaks were observed which were attributed to conformational changes taking place in the oligomer molecules upon transition to the conductive form, alongside the film's oxidative doping process. To shed some light on the issue of charge carriers appearing in the film upon its oxidation, supplemental ESR spectroelectrochemical measurements were carried out and confirmed that, radical cations are generated in the film.

In situ ESR spectroelectrochemical studies of poly(3,4-ethylenedioxythiophene) (PEDOT) have been performed, in an attempt to take a closer look at species responsible for the conductivity of the polymer in the doped state. A series of ESR spectra at progressively changed potentials applied to the polymer film in the oxidation and subsequently, reduction half-cycles were recorded. The results reveal distinct ESR lines with a noteworthy concentration of spins in the reduced state of the polymer and marked changes in both the intensities and ΔBpp widths of the ESR signal across the studied potential range, indicating non-trivial changes in the character of charge carriers with changing potential. Also, interesting phenomena like the potential hysteresis of the spin concentration and of ΔBpp linewidths between the oxidation and reduction cycles of the polymer are observed. The presence of residual spins in the polymer in the reduced state may indicate that at least to some partial extent, PEDOT chains exist in the quinoid rather than benzoid configuration in the dedoped state. Hysteresis of spectroscopic parameters may imply that certain hindrance factors like slow anion expulsion speed accompany the dedoping process of the polymer. Keywords: Electrochemistry, PEDOT, ESR spectroscopy, Polarons, Bipolarons

In situ EPR spectroelectrochemical studies of two members of poly(3,4-alkylenedioxythiophene) family of polymers, namely poly(3,4-ethylenedioxythiophene) – PEDOT and poly(3,4-butylenedioxythiophene) – PBuDOT have been performed with an aim to investigate the effect of doping and subsequent dedoping on charge carriers in these polymers. The objectives of investigations were to characterise the type of paramagnetic centres appearing in the polymer and to observe the influence of doping on their concentration and other spectroscopic properties. It was found that the evolution of spins in both polymers upon doping follows a trend similar to that observed for other thiophene-based polymers. The characteristic points of these curves are different however for each polymer. The maximum spin concentration in PEDOT takes place at 0.2 V and for PBuDOT it is at 0.35 V. While generally similar in behaviour during doping, the behaviour of these two polymers upon dedoping is markedly different. For PBuDOT the concentration of spins follows a more or less reverse path of the doping curve whereas in PEDOT a hysteresis of concentration of spins appears. Similar trends are observed for the signals’ ΔBpp widths. Both polymers display distinct narrow EPR lines at the end of the reduction half-cycle suggesting that a noteworthy concentration of spins exist in them even in the fully reduced (dedoped) state. Analysis of the EPR spectra of the polymers in their doped states revealed their complex character. It was found that these complex spectra could be decomposed into two separate components – one Gaussian and one Lorentzian. Based on EPR microwave saturation studies the Gaussian component was attributed to highly mobile polarons which are confined in isolated spin packets and the Lorentzian one to delocalised less mobile polarons, homogeneously distributed within the material, which thus could be associated with the electrons of conductivity.

A series of hybrid tetrathiafulvalene-oligothiophene compounds has been synthesised, where the tetrathiafulvalene unit is fused at each side to an end-capped oligothiophene chain of varying length (terthiophene, quinquithiophene and septithiophene). Each hybrid structure (1-3) has been studied by cyclic voltammetry and triple EPR-UV-Vis-NIR spectroelectrochemistry in the case of the quinquithiophene compound (2). Comparison is made with the corresponding half-units, which lack the fulvalene core and contain just one oligothiophene chain. The highest hole mobility of quinquithiophene-TTF 2 was obtained from field effect transistors (8.61 × 10-3 cm 2 V-1 s-1); its surface morphology was characterised by tapping mode atomic force microscopy and a power conversion of 2.5% was achieved from a bulk heterojunction organic solar cell device using PC71BM as the acceptor.

We prepared 2,3,4,5-tetrahydrothieno[3,4-b][1,4]dioxocine- BuDOT and [3,4-b][3',4'-l]-dithieno-1,4,11,14-tetraoxacycloeicosane. We tried to electropolymerise both and found that while BuDOT polymerises easily the second monomer shows difficulty polymerising in organic solvents used. Electrochemical stability of PBuDOT was investigated using cyclic voltammetry and the polymer was found to be stable in the (-0.6 V) 1.55 V potential range.

In an effort to extend the conjugation system of boron-dipyrrin (BODIPY), the dye was coupled with polymerisable units of carbazole, alkylthiophene, and 3,4-ethylenedioxythiophene (EDOT). Due to electron donating character of the units connected to the strong electron accepting segment of tri-coordinated boron, the optical and electrochemical properties of the dye changed, and followed the strength of the electron donating substituent. All studied compounds exhibited electroactivity in both anodic and cathodic potential ranges, however, electropolymerisation was only observed for BODIPY modified with EDOT, leading to trimeric and tetrameric substituents. Potential controlled optical changes (spectroelectrochemistry) and in situ spin density distribution measurements, supported by quantum chemical calculations using density functional theory, were undertaken in order to understand the reversibility of the electrochemical processes. Hyperfine split ESR spectra of the radical anion species were successfully modelled revealing intriguing, hyperconjugation type unpaired spin delocalisation patterns.