Exploring the Influence of P3HT on PTCA Crystallization and Phase Behavior in Thin Films.

The thermal properties and alignment of crystallinity of materials in thin films play crucial roles in the performance and reliability of various devices, especially in the fields of electronics, materials science, and engineering. The slight variations in the molecular packing of the active layer can make considerable differences in the optical and thermal properties. Herein, we aim to investigate the tuning of the physical properties of a blended thin film of n-type small organic molecules of perylene-3,4,9,10-tetracarboxylic acid (PTCA-SMs) with the mixing of the p-type polymer poly(3-hexylthiophene) (P3HT). The resulting thin films exhibit an enhanced surface crystallinity compared to the pristine material, leading to the formation of long crystallites, and these crystallites are thermally stable in the solid state, as confirmed by X-ray diffraction (XRD), atomic force microscopy (AFM), and thermal analysis using variable-temperature spectroscopic ellipsometry (VTSE) and differential scanning calorimetry (DSC). We believe that the crystalline structure of the obtained P3HT/PTCA-SMs blends is a combination of edge-on and face-on orientations, which enable the potential use of this material as an active layer in organic electronics.

N,N-Bis(9-methyl-3-carbazolyl)-4-anisidine as an Electroactive Material for Use in Perovskite Solar Cells.

Di(9-methyl-3-carbazolyl)-(4-anisyl)amine is presented as an effective hole-transporting material suitable for application in perovskite solar cells. It is obtained by a three-step synthesis from inexpensive starting compounds. It has a relatively high glass transition temperature of 93 °C and thermal stability with 5% weight loss at 374 °C. The compound exhibits reversible double-wave electrochemical oxidation below +1.5 V and polymerization at higher potential. A mechanism for its oxidation is proposed based on electrochemical impedance and electron spin resonance spectroscopy investigations, ultraviolet-visible-near-infrared absorption spectroelectrochemistry results, and density functional theory-based calculations. Vacuum-deposited films of the compound are characterized by a low ionization potential of 5.02 ± 0.06 eV and hole mobility of 10-3 cm2/(Vs) at an electric field of 4 × 105 V/cm. The newly synthesized compound has been used to fabricate dopant-free hole-transporting layers in perovskite solar cells. A power conversion efficiency of 15.5% was achieved in a preliminary study.

Naphthalene Phthalimide Derivatives as Model Compounds for Electrochromic Materials.

Electrochromism of organic compounds is a well-known phenomenon; however, nowadays, most research is focused on anodic coloring materials. Development of efficient, cathodic electrochromic materials is challenging due to the worse stability of electron accepting materials compared with electron donating ones. Nevertheless, designing stable cathodic coloring organic materials is highly desired-among other reasons-to increase the coloration performance. Hence, four phthalimide derivatives named 1,5-PhDI, 1,4-PhDI, 2,6-PhDI and 3,3'-PhDI were synthesized and analyzed in depth. In all cases, two imide groups were connected via naphthalene (1,5-PhDI, 1,4-PhDI, 2,6-PhDI) or 3,3'-dimethylnaphtidin (3,3'-PhDI) bridge. To observe the effect of chemical structure on physicochemical properties, various positions of imide bond were considered, namely, 1,5- 1,4- and 2,6-. Additionally, a compound with the pyromellitic diimide unit capped with two 1-naphtalene substituents was obtained. All compounds were studied in terms of their thermal behavior, using differential calorimetry (DSC) and thermogravimetric analysis (TGA). Moreover, electrochemical (CV, DPV) and spectroelectrochemical (UV-Vis and EPR) analyses were performed to evaluate the obtained materials in terms of their application as cathodic electrochromic materials. All obtained materials undergo reversible electrochemical reduction which leads to changes in their optical properties. In the case of imide derivatives, absorption bands related to both reduced and neutral forms are located in the UV region. However, importantly, the introduction of the 3,3'-dimethylnaphtidine bridge leads to a noticeable bathochromic shift of the reduced form absorption band of 3,3'-PhDI. This indicates that optimization of the phthalimide structure allows us to obtain stable, cathodic electrochromic materials.

UV-vis and ECD spectroelectrochemistry of atropisomeric naphthalenediimide derivative.

The UV-vis and ECD spectroelectrochemistry (SEC) of a chiral binaphthalenylamine derivative of the N-butyl naphthalenediimide (NDIB-NH2) enantiomers were applied to measure UV-vis and ECD spectra of NDIB-NH2 radicals and dianion formed in the reduction and oxidation processes observed in cyclic voltammetry (CV). The CV curves and EPR spectroelectrochemistry enabled us to establish conditions at which a radical-anion [NDIB-NH2]̇.-, a dianion [NDIB-NH2]2-, and a radical-cation [NDIB-NH2]̇.+ are formed. The DFT restricted open-shell CAM-B3LYP-D3/def2TZVP/PCM calculations demonstrated that in the radical-anion [NDIB-NH2]̇.-, spin is spread over the NDI system while in the radical-cation [NDIB-NH2]̇+ it is spread over the aminonaphthalene moiety. The UV-vis spectra of radical-anion and dianion show the most significant changes in the 400-800 nm range. In that range, the ECD spectra varied with the change of electrode potential more than the UV-vis did and enabled the identification of a new ECD band of [NDIB-NH2]̇.- at ca. 400 nm hidden in the background in the UV spectra at -1000 mV. A broad structured ECD pattern with a maximum at ca. 530 nm was observed for [NDIB-NH2]̇.- (-1000 mV), while a single smooth ECD band of [NDIB-NH2]2- was located at 520 nm (-1750 mV). For the first time, an isosbestic point (455 nm) was found in ECD spectroelectrochemical measurements for the radical-cation [NDIB-NH2]̇.+ in equilibrium with the NDIB-NH2 neutral form. The TD-DFT CAM-B3LYP-D3/6-31G** calculations combined with the hybrid (explicit combined with implicit) solvation model fairly well reproduced the UV-vis and ECD SEC of neutral and redox forms of NDIB-NH2 but the ECD spectrum of [NDIB-NH2]̇.+ above 390 nm.

The Role of Electrochemical and Spectroelectrochemical Techniques in the Preparation and Characterization of Conjugated Polymers: From Polyaniline to Modern Organic Semiconductors.

This review article presents different electrochemical and spectroelectrochemical techniques used to investigate conjugated polymers. The development of this research area is presented from an over 40-year perspective-the period of research carried out by Professor Mieczyslaw Lapkowski. Initial research involved polymers derived from simple aromatic compounds, such as polyaniline. Since then, scientific advances in the field of conductive polymers have led to the development of so-called organic electronics. Electrochemical and spectroelectrochemical methods have a great influence in the development of organic semiconductors. Their potential for explaining many phenomena is discussed and the most relevant examples are provided.

Potent strategy towards strongly emissive nitroaromatics through a weakly electron-deficient core.

Nitroaromatics seldom fluoresce. The importance of electron-deficient (n-type) conjugates, however, has inspired a number of strategies for suppressing the emission-quenching effects of the strongly electron-withdrawing nitro group. Here, we demonstrate how such strategies yield fluorescent nitroaryl derivatives of dipyrrolonaphthyridinedione (DPND). Nitro groups near the DPND core quench its fluorescence. Conversely, nitro groups placed farther from the core allow some of the highest fluorescence quantum yields ever recorded for nitroaromatics. This strategy of preventing the known processes that compete with photoemission, however, leads to the emergence of unprecedented alternative mechanisms for fluorescence quenching, involving transitions to dark nπ* singlet states and aborted photochemistry. Forming nπ* triplet states from ππ* singlets is a classical pathway for fluorescence quenching. In nitro-DPNDs, however, these ππ* and nπ* excited states are both singlets, and they are common for nitroaryl conjugates. Understanding the excited-state dynamics of such nitroaromatics is crucial for designing strongly fluorescent electron-deficient conjugates.

Perinone-New Life of an Old Molecule.

A review of publications on the synthesis and properties of a family of compounds called perinones was carried out. The basic molecule has been known for several decades mainly as a photostable pigment, and in recent years it has become increasingly used in organic electronics. This paper describes the methods of synthesis of low molecular weight compounds and polymers based on that molecule; the basic spectroscopic, photochemical, electrochemical and electronic properties important for the construction of organic electronics and optoelectronics devices are also discussed.

Chemical and Electronic Structure Characterization of Electrochemically Deposited Nickel Tetraamino-phthalocyanine: A Step toward More Efficient Deposition Techniques for Organic Electronics Application.

Phthalocyanines (Pc), with or without metal ligands, are still of high research interest, mainly for the application in organic electronics. Because of rather low solubility, Pc-based films are commonly deposited applying various advanced and demanding vacuum techniques, like physical vapor deposition (PVD). In this work, an alternative straightforward approach of NiPc layer formation is proposed in which NH2-side groups of nickel(II) tetraamino-phthalocyanine (AmNiPc) are engaged in the process of electrochemical deposition of (AmNiPc)layer on indium-tin oxide (ITO) substrates. The resulting layer is widely investigated by cyclic voltammetry, atomic force microscopy, UV-vis, and ATR-IR spectroscopies, X-ray diffraction, and photoemission techniques: X-ray and UV-photoelectron spectroscopies. The chemical and electronic structure of (AmNiPc)layer is characterized. It is shown that the electronic properties of the formed (AmNiPc)layer/ITO hybrid correspond to the ones previously reported for PVD-NiPc films.

Electrically-responsive antimicrobial coatings based on a tetracycline-loaded poly(3,4-ethylenedioxythiophene) matrix.

The growth of bacteria and the formation of complex bacterial structures on biomedical devices is a major challenge in modern medicine. The aim of this study was to develop a biocompatible, conducting and antibacterial polymer coating applicable in biomedical engineering. Since conjugated polymers have recently aroused strong interest as controlled delivery systems for biologically active compounds, we decided to employ a poly(3,4-ethylenedioxythiophene) (PEDOT) matrix to immobilize a powerful, first-line antibiotic: tetracycline (Tc). Drug immobilization was carried out simultaneously with the electrochemical polymerization process, allowing to obtain a polymer coating with good electrochemical behaviour (charge storage capacity of 19.15 ± 6.09 mC/cm2) and high drug loading capacity (194.7 ± 56.2 µg/cm2). Biological activity of PEDOT/Tc matrix was compared with PEDOT matrix and a bare Pt surface against a model Gram-negative bacteria strain of Escherichia coli with the use of LIVE/DEAD assay and SEM microscopy. Finally, PEDOT/Tc was shown to serve as a robust electroactive coating exhibiting antibacterial activity.

Electrochemical and Spectroelectrochemical Studies on the Reactivity of Perimidine-Carbazole-Thiophene Monomers towards the Formation of Multidimensional Macromolecules versus Stable π-Dimeric States.

During research on cross-linked conducting polymers, double-functionalized monomers were synthesized. Two subunits potentially able to undergo oxidative coupling were used-perimidine and, respectively, carbazole, 3,6-di(hexylthiophene)carbazole or 3,6-di(decyloxythiophene)carbazole; alkyl and alkoxy chains as groups supporting molecular ordering and 14H-benzo[4,5]isoquinone[2,1-a]perimidin-14-one segment promoting CH⋯O interactions and π-π stacking. Electrochemical, spectroelectrochemical, and density functional theory (DFT) studies have shown that potential-controlled oxidation enables polarization of a specific monomer subunit, thus allowing for simultaneous coupling via perimidine and/or carbazole, but mainly leading to dimer formation. The reason for this was the considerable stability of the dicationic and tetracationic π-dimers over covalent bonding. In the case of perimidine-3,6-di(hexylthiophene)carbazole, the polymer was not obtained due to the steric hindrance of the alkyl substituents preventing the coupling of the monomer radical cations. The only linear π-conjugated polymer was obtained through di(decyloxythiophene)carbazole segment from perimidine-di(decyloxythiophene)-carbazole precursor. Due to the significant difference in potentials between subsequent oxidation states of monomer, it was impossible to polarize the entire molecule, so that both directions of coupling could be equally favored. Subsequent oxidation of this polymer to polarize the side perimidine groups did not allow further crosslinking, because rather the π-π interactions between these perimidine segments dominate in the solid product.

2,1,3-Benzothiadiazole Small Donor Molecules: A DFT Study, Synthesis, and Optoelectronic Properties.

We herein report the design and synthesis of small-donor molecules, 2,1,3-benzothiadiazole derivatives (2a-d), by Stille or Suzuki reaction. The synthesized compounds were characterized by spectroscopic and electrochemical methods. The compounds 2a-d absorb the light in a wide range (the UV-green/yellow light (2c)) and emit from green to red/near IR light (2c). Furthermore, these compounds show a narrow energy gap (1.75-2.38 eV), and high Ea values increasing for polymers, which prove their electron-donating nature and semiconductor properties. The measurements were enhanced by theoretical modeling.

ECD spectroelectrochemistry: A review.

The electronic circular dichroism (ECD) spectroscopy is probably the most important chiraloptical method, and the role of chirality in contemporary chemistry, pharmacy, and material science constantly increases. On the other hand, the electrochemical methods are also very sensitive tools for studying multivarious redox processes. Nevertheless, the first ECD spectroelectrochemical (SEC) study was only published by Daub, Salbeck and Aurbach in 1988, and since then, the ECD SEC method has been mentioned in only thirty papers. By the summer of 2020, the ECD SEC studies were mainly focused around molecular systems for organic, and marginally, inorganic chiroptical switching studies of biochemical redox reactions. The review provides more details about the ECD SEC studies carried out so far. At the end, we suggest some future applications for the ECD spectroelectrochemistry.

Going beyond the borders: pyrrolo[3,2-b]pyrroles with deep red emission.

A two-step route to strongly absorbing and efficiently orange to deep red fluorescent, doubly B/N-doped, ladder-type pyrrolo[3,2-b]pyrroles has been developed. We synthesize and study a series of derivatives of these four-coordinate boron-containing, nominally quadrupolar materials, which mostly exhibit one-photon absorption in the 500-600 nm range with the peak molar extinction coefficients reaching 150 000, and emission in the 520-670 nm range with the fluorescence quantum yields reaching 0.90. Within the family of these ultrastable dyes even small structural changes lead to significant variations of the photophysical properties, in some cases attributed to reversal of energy ordering of alternate-parity excited electronic states. Effective preservation of ground-state inversion symmetry was evidenced by very weak two-photon absorption (2PA) at excitation wavelengths corresponding to the lowest-energy, strongly one-photon allowed purely electronic transition. π-Expanded derivatives and those possessing electron-donating groups showed the most red-shifted absorption- and emission spectra, while displaying remarkably high peak 2PA cross-section (σ 2PA) values reaching ∼2400 GM at around 760 nm, corresponding to a two-photon allowed higher-energy excited state. At the same time, derivatives lacking π-expansion were found to have a relatively weak 2PA peak centered at ca. 800-900 nm with the maximum σ 2PA ∼50-250 GM. Our findings are augmented by theoretical calculations performed using TD-DFT method, which reproduce the main experimental trends, including the 2PA, in a nearly quantitative manner. Electrochemical studies revealed that the HOMO of the new dyes is located at ca. -5.35 eV making them relatively electron rich in spite of the presence of two B--N+ dative bonds. These dyes undergo a fully reversible first oxidation, located on the diphenylpyrrolo[3,2-b]pyrrole core, directly to the di(radical cation) stage.

Enantioselective sensing of (S)-Thalidomide in blood plasma with a chiral naphthalene diimide derivative.

Fast, simple in use and highly effective voltammetric enantiosensor dedicated for determination of thalidomide (TD) enantiomers (especially towards the toxic (S)-enantiomer) in blood plasma is still desirable. Here we have proven that newly synthesized chiral naphthalene diimide (NDI) derivatives are excellent electroactive materials for TD enantiosensors. The recognition process relies on the specific interaction between the chiral NDI receptor and the thalidomide enantiomer of the opposite configuration. This unique specific interaction between (S)-thalidomide and (R)-NDI derivative counterparts, evident in the DPV voltammograms, was confirmed by molecular modeling. The demonstrated voltammetric enantiosensors are characterized by the low detection limit at the level of µg·L-1, wide analytical range from 5·10-4 - 10 mg·L-1, high selectivity and long lifetime. The results of the recovery rates showed a very good degree of accuracy towards the determination of (S)-thalidomide in the blood samples, so it can be successfully used in the analysis of clinical samples.

An Insight into Ionic Conductivity of Polyaniline Thin Films.

The work addresses an issue of the conductivity phenomenon in conductive polymer thin films. Polyaniline was chosen as a broadly used and thoroughly investigated conductive polymer in order to test and show capabilities of the developed original approach based on impedance spectra analysis. A number of films of different thickness were deposited onto a Pt electrode surface and consequently investigated in aqueous solution containing perchloric acid as an electrolyte. The processes that occur in polyaniline film were studied by cyclic voltammetry, electrochemical quartz crystal microgravimetry (EQCM) and electrochemical impedance spectroscopy (EIS). The role of incorporated ions as charge carriers was investigated with respect to the control of the conductivity properties of the film. Along with detailed polyaniline behavior study, the work makes up a fundamental scientific impact on theoretical electrochemistry and electroanalytical techniques.

Bacterial Surface Colonization of Sputter-Coated Platinum Films.

Due to its biocompatibility and advantageous electrochemical properties, platinum is commonly used in the design of biomedical devices, e.g., surgical instruments, as well as electro-medical or orthopedic implants. This article verifies the hypothesis that a thin layer of sputter-coated platinum may possess antibacterial effects. The purpose of this research was to investigate the adhesion and growth ability of a model strain of Gram-negative bacteria, Escherichia coli, on a surface of a platinum-coated glass slide. Although some previous literature reports suggests that a thin layer of platinum would inhibit the formation of bacterial biofilm, the results of this study suggest otherwise. The decrease in the number of bacterial cells attached to the platinum-coated glass, which was observed within first three hours of culturing, was found to be a short-time effect, vanishing after 24 h. Consequently, it was shown that a thin layer of sputter-coated platinum did not exhibit any antibacterial effect. For this reason, this study indicates an urgent need for the development of new methods of surface modification that could reduce bacterial surface colonization of platinum-based biomedical devices.

Effect of ß-Ketoiminato Ancillary Ligand Modification on Emissive Properties of New Iridium Complexes.

A series of new bis(benzo[h]quinolinato) Ir(III) complexes with modified ß-ketoiminato ancillary ligands were synthesized, and their electrochemical, photophysical properties were determined with the support of theoretical calculations. Moreover, all the synthesized heteroleptic Ir(III) complexes were examined as dopants of the host-guest type emissive layers in solution-processed phosphorescent organic light emitting diodes (PhOLEDs) of a simple structure. As expected on the basis of voltammetry measurements as well as DFT calculations, all the compounds appeared to be green emitters. Their examination showed that alteration of ß-ketoiminato ligand structure causes frontier orbitals' energy levels to be slightly changed, while significantly affecting photoluminescence and electroluminescence efficiencies of iridium phosphors containing these ligands. It was also found that modification of ancillary ligands might enhance charge trapping on the dopant, thus increasing its efficiency, especially in electroluminescence. From among the iridium complexes studied, the compound bearing 1-naphthyl group bonded to the nitrogen atom of the ancillary ligand proved to be the most efficient emitter. The PhOLED fabricated on the basis of this dopant has reached a luminance level of 16000 cd/m2, current efficiency close to 12 cd/A, and an external quantum efficiency around 3.2%.

Synthesis and Properties of New Dithienosilole Derivatives as Luminescent Materials.

Three new organosilicon compounds based on dithienosilole (DTSi) were synthesized in good yields. We report the optical and electrochemical properties of the resulting derivatives. We find that these compounds absorb the light in the ultraviolet and blue light range, and they exhibit luminescence in almost the entire range of visible light. After electropolymerization were significantly lowered, the values of the energy gap (even 1.51 eV for P2) and the ionization potential of the polymers were compared to monomers. Optoelectronic properties of the obtained compounds suggest that these derivatives of DTSi may be good candidates as the emissive layers in white organic light-emitting diodes (WOLEDs), which would reduce the amount of layers.

Spectroelectrochemistry of poly(3-hexylthiophenes) in solution.

ABSTRACT: 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.

Investigation of the Effects of Non-Conjugated Co-Grafts on the Spectroelectrochemical and Photovoltaic Properties of Novel Conjugated Graft Copolymers Based on Poly(3-hexylthiophene).

A new type of polysiloxane copolymers, with conjugated⁻regioregular poly(3-hexylthiophene) (P3HT) and non-conjugated-poly(ethylene glycol) (PEG)-grafts have been synthesised, and their properties have been studied alongside those of the parent conjugated polymer (P3HT). Spectroelectrochemical and conductometric analyses revealed an early rise of the conductance of the polymers. Once spectral changes begin taking place, the conductance is stable, implying a loss of mobility of charge carriers, even though standard doping/dedoping patterns are observed. Prototype bulk heterojunction solar cells have been fabricated, based on P3HT/[6,6]-Phenyl-C61-butyric acid methyl ester (PCBM), as well as by substituting P3HT for each of the copolymers. The prototype solar cells achieved PCEs of up to 2.11%. This is one of the highest reported power conversion efficiency (PCE) for devices based on P3HT with low average molecular weight Mn = 12 kDa. Strong correlation between the structure of the copolymer and its photovoltaic performance was found. Elongation of PEG copolymer chain and the use of methyl group instead of terminal hydroxyl groups significantly improved photovoltaic performance.