Stable n-Type Perylene Derivative Ladder Polymer with Antiambipolarity for Electrically Reconfigurable Organic Logic Gates.

Organic electrochemical transistors (OECTs) are one of the promising building blocks to realize next-generation bioelectronics. To date, however, the performance and signal processing capabilities of these devices remain limited by their stability and speed. Herein, the authors demonstrate stable and fast n-type organic electrochemical transistors based on a side-chain-free ladder polymer, poly(benzimidazoanthradiisoquinolinedione). The device demonstrated fast normalized transient speed of 0.56 ± 0.17 ms um-2 and excellent long-term stability in aqueous electrolytes, with no significant drop in its doping current after 50 000 successive doping/dedoping cycles and 2-month storage at ambient conditions. These unique characteristics make this polymer especially suitable for bioelectronics, such as being used as a pull-down channel in a complementary inverter for long-term stable detection of electrophysiological signals. Moreover, the developed device shows a reversible anti-ambipolar behavior, enabling reconfigurable electronics to be realized using a single material. These results go beyond the conventional OECT and demonstrate the potential of OECTs to exhibit dynamically configurable functionalities for next-generation reconfigurable electronics.

Surface charge as activity descriptors for electrochemical CO2 reduction to multi-carbon products on organic-functionalised Cu.

Intensive research in electrochemical CO2 reduction reaction has resulted in the discovery of numerous high-performance catalysts selective to multi-carbon products, with most of these catalysts still being purely transition metal based. Herein, we present high and stable multi-carbon products selectivity of up to 76.6% across a wide potential range of 1 V on histidine-functionalised Cu. In-situ Raman and density functional theory calculations revealed alternative reaction pathways that involve direct interactions between adsorbed histidine and CO2 reduction intermediates at more cathodic potentials. Strikingly, we found that the yield of multi-carbon products is closely correlated to the surface charge on the catalyst surface, quantified by a pulsed voltammetry-based technique which proved reliable even at very cathodic potentials. We ascribe the surface charge to the population density of adsorbed species on the catalyst surface, which may be exploited as a powerful tool to explain CO2 reduction activity and as a proxy for future catalyst discovery, including organic-inorganic hybrids.

π-Extended Poly(benzimidazoanthradiisoquinolinedione) Ladder-type Conjugated Polymer.

Since the 1960s, poly(benzobisimidazobenzophenathrolinedione) (BBL) has been the only n-type ladder-type conjugated polymer (LCP) that is utilized in thin film electronic devices. Its high electrochemical and thermal stabilities make it a promising candidate for organic electrochemical transistors (OECTs) and thermoelectrics (OTEs) applications. Here we report the synthesis and characterization of a new π-extended poly(benzimidazoanthradiisoquinolinedione) (BAL). The tetrachlorinated BAL (Cl4-BAL) is fully soluble in methanesulfonic acid (MSA) and can be spin-coated into good quality thin films, enabling the fabrication and characterization of OTEs. Doping of Cl4-BAL films using our in-house benzyl viologen radical cation (BV●+) n-dopant shows better electrical air-stability as compared to BBL due to its very low LUMO value (-4.83 eV), making it a promising material toward air-stable n-doped conducting polymers.

All-Polymer Bulk-Heterojunction Organic Electrochemical Transistors with Balanced Ionic and Electronic Transport.

The rapid development of organic electrochemical transistor (OECTs)-based circuits brings new opportunities for next-generation integrated bioelectronics. The all-polymer bulk-heterojunction (BHJ) offers an attractive, inexpensive alternative to achieve efficient ambipolar OECTs, and building blocks of logic circuits constructed from them, but have not been investigated to date. Here, the first all-polymer BHJ-based OECTs are reported, consisting of a blend of new p-type ladder conjugated polymer and a state-of-the-art n-type ladder polymer. The whole ladder-type polymer BHJ also proves that side chains are not necessary for good ion transport. Instead, the polymer nanostructures play a critical role in the ion penetration and transportation and thus in the device performance. It also provides a facile strategy and simplifies the fabrication process, forgoing the need to pattern multiple active layers. In addition, the development of complementary metal-oxide-semiconductor (CMOS)-like OECTs allows the pursuit of advanced functional logic circuitry, including inverters and NAND gates, as well as for amplifying electrophysiology signals. This work opens a new approach to the design of new materials for OECTs and will contribute to the development of organic heterojunctions for ambipolar OECTs toward high-performing logic circuits.

Facile Synthesis of Solubilizing a Group-Free, Solution-Processable p-Type Ladder Conjugated Polymer and Its Thermoelectric Properties.

Here we report the synthesis of a new solubilizing group-free, solution-processable p-type ladder conjugated polymer, 6H-pyrrolo[3,2-b:4,5-b']bis[1,4]benzothiazine ladder (PBBTL) polymer by using a polyphosphoric acid (PPA) and phenylphosphonic acid (PhPO3H2) 1:1 binary acid solvent system together with careful control of reaction kinetics. With a good intrinsic viscosity of 3.69 dL/g in methanesulfonic acid (MSA), good quality PBBTL films can be obtained via spin-coating. Intrinsic thin film properties and thermoelectric performance of PBBTL were evaluated, making it the second solubilizing group-free, solution-processable ladder-type conjugated polymer after BBL to be used for thin-film polymer electronics. While our preliminary thermoelectric performance of the FeCl3-doped PBBTL films is modest, we believe that many opportunities lie ahead for PBBTL and hope that its successful synthesis using the new PPA:PhPO3H2 binary acid solvent system will inspire synthetic organic chemists to relook into solubilizing group-free, solution-processable ladder-type conjugated polymer systems.

Polaron Delocalization Dependence of the Conductivity and the Seebeck Coefficient in Doped Conjugated Polymers.

Conjugated polymers are promising materials for thermoelectrics as they offer good performances at near ambient temperatures. The current focus on polymer thermoelectric research mainly targets a higher power factor (PF; a product of the conductivity and square of the Seebeck coefficient) through improving the charge mobility. This is usually accomplished via structural modification in conjugated polymers using different processing techniques and doping. As a result, the structure-charge transport relationship in conjugated polymers is generally well-established. In contrast, the relationship between the structure and the Seebeck coefficient is poorly understood due to its complex nature. A theoretical framework by David Emin (Phys. Rev. B, 1999, 59, 6205-6210) suggests that the Seebeck coefficient can be enhanced via carrier-induced vibrational softening, whose magnitude is governed by the size of the polaron. In this work, we seek to unravel this relationship in conjugated polymers using a series of highly identical pro-quinoid polymers. These polymers are ideal to test Emin's framework experimentally as the quinoid character and polaron delocalization in these polymers can be well controlled even by small atomic differences (<10 at. % per repeating unit). By increasing the polaron delocalization, that is, the polaron size, we demonstrate that both the conductivity and the Seebeck coefficient (and hence PF) can be increased simultaneously, and the latter is due to the increase in the polaron's vibrational entropy. By using literature data, we also show that this phenomenon can be observed in two closely related diketopyrrolopyrrole-conjugated polymers as well as in p-doped P3HT and PANI systems with an increasing molecular order.

Carboxylic Acid Directed C-H Arylation of Azulene.

The first example of directed C-H activation for azulene is reported. A variety of 2-arylazulenes are obtainable exclusively from 1-azulene carboxylic acids, with yields of up to 82%. Some heteroaryl groups such as pyridine and thiophene are also tolerated in the reaction. The efficacy of the reaction is found to be highly dependent on the conditions, with a phosphate base and a bulky carboxylic acid being key additives.

The role of fluoride in anion-π interaction with naphthalene diimide.

The role of fluoride in anion-π interaction with naphthalene diimide (NDI) is dependent on the solvent used. Here we show that in polar aprotic solvents like THF which does not contain any acidic protons, fluoride generates hydroxide that complexes with NDI and it is this complex that reduces NDI to NDI˙-.

Anion-π interactions of highly π-acidic dipyridinium-naphthalene diimide salts.

A highly π-acidic dipyridinium-naphthalene diimide acceptor shows anion-π interactions with halides and PF6-. Lewis basicity and redox potential of the anion affect the chemistry, and photophysical and electrochemical properties, as well as both ionic and electrical conductivities. Our results provide insights into doping, degradation and ion transport mechanisms in organic n-type semiconductors.

Can time-dependent density functional theory predict intersystem crossing in organic chromophores? A case study on benzo(bis)-X-diazole based donor-acceptor-donor type molecules.

Here we utilized new diagnostic tools in time-dependent density functional theory to explain the trend of intersystem crossing in benzo(bis)-X-diazole based donor-acceptor-donor type molecules. These molecules display a wide range of fluorescence quantum yields and triplet yields, making them excellent candidates for testing the validity of these diagnostic tools. We believe that these tools are cost-effective and can be applied to structurally similar organic chromophores to predict/explain the trends of intersystem crossing, and thus fluorescence quantum yields and triplet yields without the use of complex and expensive multireference configuration interaction or multireference pertubation theory methods.

Conjugated polymer energy level shifts in lithium-ion battery electrolytes.

The ionization potentials (IPs) and electron affinities (EAs) of widely used conjugated polymers are evaluated by cyclic voltammetry (CV) in conventional electrochemical and lithium-ion battery media, and also by ultraviolet photoelectron spectroscopy (UPS) in vacuo. By comparing the data obtained in the different systems, it is found that the IPs of the conjugated polymer films determined by conventional CV (IPC) can be correlated with UPS-measured HOMO energy levels (EH,UPS) by the relationship EH,UPS = (1.14 ± 0.23) × qIPC + (4.62 ± 0.10) eV, where q is the electron charge. It is also found that the EAs of the conjugated polymer films measured via CV in conventional (EAC) and Li(+) battery (EAB) media can be linearly correlated by the relationship EAB = (1.07 ± 0.13) × EAC + (2.84 ± 0.22) V. The slopes and intercepts of these equations can be correlated with the dielectric constants of the polymer film environments and the redox potentials of the reference electrodes, as modified by the surrounding electrolyte, respectively.

Synthesis and characterization of a series of annelated benzotriazole based polymers with variable bandgap.

Here we report the synthesis and characterization of a series of annelated benzotriazole based polymers with variable bandgap. Benzobistriazole monomers reported by us previously were desymmetrized using partial reduction ring opening followed by ring closure to produce a wide range of annelated benzotriazole based monomers. These monomers were co-polymerized with a fluorene moiety to give polymers with bandgaps ranging from 1.16 to 2.41 eV.

One-pot synthesis of 4,8-dibromobenzo[1,2-d;4,5-d']bistriazole and synthesis of its derivatives as new units for conjugated materials.

The one-pot synthesis of 4,8-dibromobenzo[1,2-d;4,5-d']bistriazole, followed by alkylation and Stille coupling to yield three different isomeric derivatives with markedly different optoelectronic properties, is reported. These derivatives show potential as new units in organic oligomers and polymers for electronics applications.

Synthesis and characterization of [1,2,5]chalcogenazolo[3,4-f]benzo[1,2,3]triazole and [1,2,3]triazolo[3,4-g]quinoxaline derivatives.

The synthesis and characterization is reported of low bandgap [1,2,5]chalcogenazolo[3,4-f]benzo[1,2,3]triazole and [1,2,3]triazolo[3,4-g]quinoxaline derivatives that display higher solubility and stability then their thiadiazole counterparts, [1,2,5]chalcogenazolo[3,4-f]benzo[2,1,3]thiadiazole and [1,2,5]thiadiazolo[3,4-g]quinoxaline, respectively.

Synthesis of low band gap [1,2,5]-thiadiazolo[3,4-g]quinoxaline and pyrazino[2,3-g]quinoxaline derivatives by selective reduction of benzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole.

The reduction of a dithienylbenzobisthiadiazole derivative TBBT can be performed selectively so as to afford either [1,2,5]-thiadiazolo[3,4-g]quinoxaline (TQ) or pyrazino[2,3-g]quinoxaline (PQ) derivatives. This approach offers a much milder, shorter, and more efficient route to PQ and TQ derivatives than current methods. It is further shown how the optical and electrochemical properties of PQ and TQ can be tuned by choice of appropriate substituents.

One-pot synthesis of 4,8-dibromobenzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole.

A one-step synthesis of 4,8-dibromobenzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole with use of 1,2,4,5-tetraaminobenzene tetrahydrobromide and thionyl bromide in good yield is reported. This unit can then be used in the synthesis of low bandgap materials via palladium-catalyzed coupling reactions. The approach offers a quick and easy way to prepare low bandgap materials as compared to the current literature methods.

Heterojunction topology versus fill factor correlations in novel hybrid small-molecular/polymeric solar cells.

The authors present organic photovoltaic (OPV) devices comprising a small molecule electron acceptor based on 2-vinyl-4,5-dicyanoimidazole (Vinazene) and a soluble poly(p-phenylenevinylene) derivative as the electron donor. A strong dependence of the fill factor (FF) and the external quantum efficiency [incident photons converted to electrons (IPCE)] on the heterojunction topology is observed. As-prepared blends provided relatively low FF and IPCE values of 26% and 4.5%, respectively, which are attributed to significant recombination of geminate pairs and free carriers in a highly intermixed blend morphology. Going to an all-solution processed bilayer device, the FF and IPCE dramatically increased to 43% and 27%, respectively. The FF increases further to 57% in devices comprising thermally deposited Vinazene layers where there is virtually no interpenetration at the donor/acceptor interface. This very high FF is comparable to values reported for OPV using fullerenes as the electron acceptor. Furthermore, the rather low electron affinity of Vinazene compound near 3.5 eV enabled a technologically important open circuit voltage (V(oc)) of 1.0 V.