Effect of Oxidants on Properties of Electroactive Ultrathin Polyazulene Films Synthesized by Vapor Phase Polymerization at Atmospheric Pressure

A non-benzenoid aromatic hydrocarbon azulene, naturally found in plants and mushrooms, is known for its derivatives applications in medicines. However, the processability of its chemically synthesized high-capacitance polymer is constrained by the sparingly soluble nature of its polymeric form. Oxidative chemical synthesis on a desirable substrate overcomes this difficulty. In this report, polyazulene (PAz) thin films are synthesized by vapor phase polymerization at atmospheric pressure using oxidants, such as CuCl2, CuBr2, FeCl3, and FeTOS. The effect of oxidants on morphologies of PAz films is studied using atomic force microscopy and microscope imaging. Each oxidant produced distinct microstructures in the films. The films synthesized using Cu(II) salts showed organized and knitted structures, whereas Fe(III) salts formed casted sheet-like disordered arrangements. The films synthesized using CuCl2 created uniform porous film assemblies. The pre-peak formations and their splitting observed in the cyclic voltammograms revealed phase segregations in the films. Oxidant-dependent structural and chemical differences such as charge carrier formation, doping levels, and polymer chain length in the PAz films are studied by using UV–Vis and FTIR spectroscopy. The results indicated that 240 and 180 mM are the optimum concentration of CuCl2 to produce high capacitance and well-organized single- and triple-layered PAz films, respectively

The Role of the Exciplex State in Photoinduced Electron Transfer of Phytochlorin−[60]Fullerene Dyads

The photoinduced electron transfer (ET) in five structurally different phytochlorin-fullerene dyads was studied in polar and nonpolar solvents using femtosecond fluorescence up-conversion and pump−probe transient-absorption techniques. Small changes in the structures of the dyads result in considerable changes in the ET properties and allow the determination of reorganization energies of the photoinduced reactions and electronic couplings between the initial and final states. After the excitation of the phytochlorin moiety to the second excited singlet state, the dyads relax rapidly to the first excited singlet state of phytochlorin. The first excited singlet state of phytochlorin is in equilibrium with an intramolecular exciplex state. In polar benzonitrile, the exciplex undergoes an electron transfer, and a complete-charge-separated (CCS) state is formed with a quantum yield close to unity. In contrast to the previously studied phytochlorin−fullerene dyads, the dyads in the present study form the CCS state also in nonpolar toluene with a yield influenced by minor changes in the molecular structure. The new dyads have a weaker phytochlorin−fullerene interaction due to longer separation distances between the two moieties. Therefore, the energies of the exciplex states are increased, and thus, their formation rates are reduced. In addition, the rates and yields of the complete charge separations are increased both in polar and nonpolar solvents. In benzonitrile, the reorganization energies for the transitions from the exciplex to the CCS and from the CCS to the ground state are 0.38 and 1.05 eV, respectively. The electronic couplings between the corresponding initial and final states of the two transitions mentioned above are 22 and 15 cm-1

Preparation of Supercapacitors on Flexible Substrates with Electrodeposited PEDOT/Graphene Composites

Composite films consisting of poly­(3,4-ethylenedioxythiophene) (PEDOT) and graphene oxide (GO) were electrochemically polymerized by electrooxidation of EDOT in ionic liquid (BMIMBF₄) onto flexible electrode substrates. Two polymerization approaches were compared, and the cyclic voltammetry (CV) method was found to be superior to potentiostatic polymerization for the growth of PEDOT/GO films. After deposition, incorporated GO was reduced to rGO by a rapid electrochemical method of repetitive cathodic potential cycling, without using any reducing reagents. The films were characterized in 3-electrode configuration in BMIMBF₄. Symmetric supercapacitors with aqueous electrolyte were assembled from the composite films and characterized through cyclic voltammetry and galvanostatic discharge tests. It was shown that PEDOT/rGO composites have better capacitive properties than pure PEDOT or the unreduced composite film. The cycling stability of the supercapacitors was also tested, and the results indicate that the specific capacitance still retains well over 90% of the initial value after 2000 consecutive charging/discharging cycles. The supercapacitors were demonstrated as energy storages in a room light energy harvester with a printed organic solar cell and printed electrochromic display. The results are promising for the development of energy-autonomous, low-power, and disposable electronics

Cationic Imidazolium Polythiophenes: Effects of Imidazolium-Methylation on Solution Concentration-Driven Aggregation and Surface Free Energy of Films Processed from Solvents with Different Polarity

Cationic imidazolium-functionalized polythiophenes with single- or double-methylation of the imidazolium ring were used to study the impact of imidazolium-methylation on (i) the solution concentration-driven aggregation in the presence of paramagnetic probes with different ionic and hydrophobic constituents and (ii) their surface free energy (SFE) as spin-coated films deposited on plasma-activated glass. Electron paramagnetic resonance spectroscopy shows that the differences in film structuration between the polymers with different methylations originate from the early stages of aggregation. In the solid state, higher degree of imidazolium-methylation generates smaller values of total SFE, γS, (by around 2 mN/m), which could be relevant in optoelectronic applications. Methylation also causes a decrease in the polar contribution of γS (γSp), suggesting that methylation decreases the polar nature of the imidazolium ring, probably due to the blocking of its H-bonding capabilities. The values of γS obtained in the present work are similar to the values obtained for doped films of neutral conjugated polymers, such as polyaniline, poly­(3-hexylthiophene), and polypyrrole. However, imidazolium-polythiophenes generate films with a larger predominance of the dispersive component of γS (γSd), probably due to the motion restriction in the ionic functionalities in a conjugated polyelectrolyte, in comparison to regular dopants. The presence of 1,4-dioxane increases γSp, especially, in the polymer with larger imidazolium-methylation (and therefore unable to interact through H-bonding), probably by a decrease of the imidazolium–glass interactions. Singly-methylated imidazolium polythiophenes have been applied as electrode selective (“buffer”) interlayers in conventional and inverted organic solar cells, improving their performance. However, clear structure–function guidelines are still needed for designing high-performance polythiophene-based interlayer materials. Therefore, the information reported in this work could be useful for such applications