A novel high-contrast ratio electrochromic material from spiro[cyclododecane-1,9′-fluorene]bicarbazole

Overoxidation of Intrinsically Conducting Polymers

Intrinsically conducting polymers may undergo significant changes of molecular structure and material properties when exposed to highly oxidizing conditions or very positive electrode potentials, commonly called overoxidation. The type and extent of the changes depend on the experimental conditions and chemical environment. They may proceed already at much lower rates at lower electrode potentials because some of the processes associated with overoxidation are closely related to more or less reversible redox processes employed in electrochemical energy conversion and electrochromism. These changes may be welcome for some applications of these polymers in sensors, extraction, and surface functionalization, but in many cases, the change of properties affects the performance of the material negatively, contributing to material and device degradation. This report presents published examples, experimental observations, and their interpretations in terms of both structural and of material property changes. Options to limit and suppress overoxidation are presented, and useful applications are described extensively.

Improving the Electropolymerization Properties of Fluorene-Bridged Dicarbazole Monomers through Polyfluoroalkyl Side Chains

The facile functionalization of the fluorene scaffold at the 2,7-positions was utilized to provide access to two soluble carbazole-π-carbazole derivatives CFC-H1 and CFC-F1 featuring fully hydrogenated and polyfluorinated alkyl chains at the 9-position of the fluorene π-bridging unit, respectively. The optical and electrochemical properties of the new dicarbazoles were investigated. Their electrochemical polymerization over Pt and indium tin oxide electrodes allowed the generation of electroactive polymeric films, whose physicochemical characteristics were strongly dependent on the kind of alkyl chain present on the fluorene bridge. In particular, the electropolymerization of the polyfluorinated monomer allowed the fabrication of thin films with good electrical conductivity, reversible electrochemical processes, good electrochromic properties, and enhanced water repellency with respect to its nonfluorinated analogue.

Electrosynthesis of Aromatic Poly(amide-amine) Films from Triphenylamine-Based Electroactive Compounds for Electrochromic Applications

Two electropolymerizable monomers with a methoxytriphenylamine core linked via amide groups to two triphenylamine (TPA) or N-phenylcarbazole (NPC) terminal groups, namely 4,4'-bis(4-diphenylaminobenzamido)-4''-methoxytriphenylamine (MeOTPA-(TPA)₂) and 4,4'-bis(4-(carbazol-9-yl)benzamido)-4''-methoxytriphenylamine (MeOTPA-(NPC)₂), were synthesized and characterized by FTIR and ¹H NMR spectroscopy, mass spectrometry, and cyclic voltammetry. The electrochemical polymerization reactions of these MeOTPA-cored monomers over indium tin oxide (ITO) electrode allow the generation of electroactive poly(amide-amine) films. The electro-generated polymer films exhibited reversible redox processes and multi-colored electrochromic behaviors upon electro-oxidation, together with moderate coloration efficiency and cycling stability. The optical density changes (ΔOD) were observed in the range of 0.18⁻0.68 at specific absorption maxima, with the calculated coloration efficiencies of 42⁻123 cm²/C. Single-layer electrochromic devices using the electrodeposited polymer films as active layers were fabricated for the preliminary investigation of their electrochromic applications.

Facile Synthesis of Electroactive and Electrochromic Triptycene Poly(ether-imide)s Containing Triarylamine Units via Oxidative Electro-Coupling

Two bisimide compounds, TPA–TPDI and NPC–TPDI, consisting of a triptycene core and two triphenylamine (TPA) or N-phenylcarbazole (NPC) end groups were successfully synthesized by the condensation reactions from 1,4-bis(3,4-dicarboxyphenoxy)triptycene dianhydride with 4-aminotriphenylamine and N-(4-aminophenyl)carbazole, respectively. These two monomers could polymerize electrochemically via the oxidative coupling reactions of triarylamine units. The electrochemical and spectroelectrochemical properties of the electro-generated triptycene poly(ether-imide)s (TPA–TPPI and NPC–TPPI) were studied. Both polymers have two colored oxidation states, and TPA–TPPI showed better electrochromic performance than NPC–TPPI.

Electrochemical synthesis of electrochromic polycarbazole films from N-phenyl-3,6-bis(N-carbazolyl)carbazoles

Electroactive and electrochromic polycarbazole films were directly prepared on electrodes from N-phenyl-3,6-bis(N-carbazolyl)carbazoles by carbazole-based electrochemical oxidative coupling.

Electrosynthesis and electrochromic properties of poly(amide-triarylamine)s containing triptycene units

Redox-active and electrochromic films of poly(amide-triarylamine)s with triptycene units have been directly fabricated on the electrode surface via the electrochemical oxidative coupling of triphenylamine or carbazole units.

Spectroelectrochemical characterization of isomeric conjugated polymers containing 2,7- and 3,6-carbazole linked by vinylene and ethynylene segments

The ability to form multi-colored oxidation states upon applied positive potentials, and the narrow band gap of 2,7-substituted carbazole derivatives, had encouraged the development of new carbazole containing polymers with interesting optoelectronic properties. Four conjugated polymers containing substituted carbazole units spaced in the main chain by vinylene and 1,4-phenyleneethynylene segments were synthesized via Stille and Sonogashira coupling reactions. Two different substitution positions of carbazole, such as 2,7- and 3,6-carbazole were used to tune the conjugation length and the charge transfer properties of the resulting polymers. The structures of the obtained polymers were characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy while the electronic and optical properties were investigated as function of carbazole substitution positions or spacer nature by ultraviolet-visible spectroscopy and cyclic voltammetry. The redox behaviour of polymers as films deposited on working electrode was investigated using cyclic voltammetry technique, and the lowest unoccupied molecular orbital and highest unoccupied molecular orbital energy levels values were also determined. Spectroelectrochemical measurements suggested the existence of polaronic and bipolaronic structures of polymers backbones accompanied by multi-electrochromic behavior.