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Photoinduced symmetry-breaking charge separation (SB-CS) has been extensively observed in various oligomers and aggregates, which holds great potential for robust artificial solar energy conversion systems. It attaches great importance to the precise manipulation of interchromophore electronic coupling in realizing efficient SB-CS. The emerging studies on SB-CS suggested that it could be realized in null-excitonic aggregates, and a long-lived SB-CS state was observed, which offers an advanced platform and has gathered immense attention in the SB-CS field. Here, we unveiled the null-exciton coupling induced ultrafast SB-CS in a rigid polycyclic aromatic hydrocarbon framework, triperyleno[3,3,3]propellane triimides (TPPTI), in which three chromophores were attached through a nonconjugated bridge. Through a combination of theoretical calculations and steady-state absorption results, we demonstrated that this nonconjugated TPPTI possesses negligible exciton coupling. Increased solvent polarity was found to significantly enhance state mixing between local excited and charge transfer states. Using transient absorption spectroscopy, ultrafast SB-CS was observed in highly polar dimethylformamide, facilitated by a selective hole-transfer coupling and a favorable charge separation free energy (ΔGCS). Additionally, the rate ratio between SB-CS and charge recombination was at least high to 1800 in dimethylformamide. This investigation provides profound insights into the role of null-exciton coupling in dominating ultrafast SB-CS in multichromophoric systems. [ABSTRACT FROM AUTHOR]

The backwardness of n‐type organic semiconductors still exists compared with the p‐type counterparts. Thus, the development of high‐performance n‐type organic semiconductors is of great importance for organic electronic devices and their integrated circuits. In recent years, azabenzannulated perylene diimide (PDI), as one of immense bay‐region‐annulated PDI derivatives, has drawn considerable attentions. However, the electronic mobilities of azabenzannulated PDI derivatives are barely satisfactory. In this contribution, the peripheral benzene ring in azabenzannulated PDI 2 was fused to the ortho position by intramolecular C−H arylation cyclization. This endows the resultant azabenzannulated PDI 4 a planar configuration as well as electron deficient pentagonal ring. As a result, the electronic mobility of 4 is almost two orders of magnitude higher than that of the nonfused azabenzannulated PDI 2. This work shall pave a new avenue in elevating the performance of azabenzannulated PDI in organic electronics. [ABSTRACT FROM AUTHOR]

Charge transport phenomena in single-molecule junctions are often dominated by tunneling, with a transmission function dictating the probability that electrons or holes tunnel through the junction. Here, we present a new and simple technique for measuring the transmission functions of molecular junctions in the coherent tunneling limit, over an energy range of 1.5 eV around the Fermi energy. We create molecular junctions in an ionic environment with electrodes having different exposed areas, which results in the formation of electric double layers of dissimilar density on the two electrodes. This allows us to electrostatically shift the molecular resonance relative to the junction Fermi levels in a manner that depends on the sign of the applied bias, enabling us to map out the junction's transmission function and determine the dominant orbital for charge transport in the molecular junction. We demonstrate this technique using two groups of molecules: one group having molecular resonance energies relatively far from EF and one group having molecular resonance energies within the accessible bias window. Our results compare well with previous electrochemical gating data and with transmission functions computed from first principles. Furthermore, with the second group of molecules, we are able to examine the behavior of a molecular junction as a resonance shifts into the bias window. This work provides a new, experimentally simple route for exploring the fundamentals of charge transport at the nanoscale.

The development of innovative triplet materials plays a significant role in various applications. Although effective tuning of triplet formation by intersystem crossing (ISC) has been well established in solution, the modulation of ISC processes in the solid state remains a challenge due to the presence of other exciton decay channels through intermolecular interactions. The cyclic structure of cycloparaphenylenes (CPPs) offers a unique platform to tune the intermolecular packing, which leads to controllable exciton dynamics in the solid state. Herein, by integrating an electron deficient coronene diimide (CDI) unit into the CPP framework, a donor‐acceptor type of conjugated macrocycle (CDI‐CPP) featuring intramolecular charge‐transfer (CT) interaction was designed and synthesized. Effective intermolecular CT interaction resulting from a slipped herringbone packing was confirmed by X‐ray crystallography. Transient spectroscopy studies showed that CDI‐CPP undergoes ISC in both solution and the film state, with triplet generation time constants of 4.5 ns and 238 ps, respectively. The rapid triplet formation through ISC in the film state can be ascribed to the cooperation between intra‐ and intermolecular charge‐transfer interactions. Our results highlight that intermolecular CT interaction has a pronounced effect on the ISC process in the solid state, and shed light on the use of the characteristic structure of CPPs to manipulate intermolecular CT interactions. [ABSTRACT FROM AUTHOR]

Dielectric polymers with inherent flexibility, high breakdown strength, and low cost have garnered significant attention for their potential applications as energy storage mediums in advanced electronic and electrical systems. However, these current polymers exhibit a low dielectric constant and inferior thermal stability, resulting in a low energy density and limited operation temperature. In this work, we present a Langmuir–Blodgett (LB) technique-assisted approach for achieving a multilayered polyetherimide (PEI)/calcium niobate (CNO) nanocomposite with in-plane aligned CNO nanosheet layers embedded within the polymer matrix. The LB deposition technique enables a precise in-plane alignment and a densely packed arrangement of CNO nanosheets within the PEI matrix, thereby effectively impeding charge transfer and establishing a continuous heat-conducting network. Consequently, the multilayered PEI/CNO nanocomposite exhibits a significant reduction in leakage current density and an enhancement in breakdown strength at elevated temperatures compared to the pure PEI polymer. Additionally, the incorporation of CNO nanosheets also leads to an increase in the dielectric constant of the nanocomposites. Due to these improvements in the dielectric constant and high-temperature breakdown strength, the multilayered nanocomposite achieves a remarkable 180% enhancement in energy density compared to pure PEI, reaching 6.9 J cm−3 at 150 °C (with an energy efficiency exceeding 90%). Furthermore, the nanocomposite film-based multilayer polymer capacitor (MLPC) device exhibits exceptional capacitance and outstanding flexibility, showcasing the immense potential of these multilayered nanocomposite films in high-temperature electronic and electrical systems. [ABSTRACT FROM AUTHOR]

Singlet fission (SF) is a spin–allowed process in which a higher–energy singlet exciton is converted into two lower‐energy triplet excitons via a triplet pair intermediate state. Implementing SF in photovoltaic devices holds the potential to exceed the Shockley–Queisser limit of conventional single‐junction solar cells. Although great progress has been made in exploiting the underlying mechanism of SF over the past decades, the scope of materials capable of SF, particularly polymeric materials, remains poor. SF–capable polymer is one of the most potential candidates in the implementation of SF into devices due to their distinct superiorities in flexibility, solution processability and self‐assembly behavior. Notably, recent advancements have demonstrated high‐performance SF in isolated donor‐acceptor (D‐A) copolymer chains. This review provides an overview of recent progress in the development of SF‐capable polymeric materials, with a significant focus on elucidating the mechanisms of SF in polymers and optimizing the design strategies for SF‐capable polymers. Additionally, the paper discusses the challenges encountered in this field and presents future perspectives. It is expected that this comprehensive review will offer valuable insights into the design of novel SF‐capable polymeric materials, further advancing the potential for SF implementation in photovoltaic devices. [ABSTRACT FROM AUTHOR]

Polymers are desirable optoelectronic materials, stemming from their solution processability, tunable electronic properties, and large absorption coefficients. An exciting development is the recent discovery that singlet fission (SF), the conversion of a singlet exciton to a pair of triplet states, can occur along the backbone of an individual conjugated polymer chain. Compared to other intramolecular SF compounds, the nature of the triplet pair state in SF polymers remains poorly understood, hampering the development of new materials with optimized excited state dynamics. Here, we investigate the effect of solvent polarity on the triplet pair dynamics in the SF polymer polybenzodithiophene-thiophene-1,1-dioxide. We use transient emission measurements to study isolated polymer chains in solution and use the change in the solvent polarity to investigate the role of charge transfer character in both the singlet exciton and the triplet pair multiexciton. We identify both singlet fluorescence and direct triplet pair emission, indicating significant symmetry breaking. Surprisingly, the singlet emission peak is relatively insensitive to solvent polarity despite its nominal "charge-transfer" nature. In contrast, the redshift of the triplet pair energy with increasing solvent polarity indicates significant charge transfer character. While the energy separation between singlet and triplet pair states increases with solvent polarity, the overall SF rate constant depends on both the energetic driving force and additional environmental factors. The triplet pair lifetime is directly determined by the solvent effect on its overall energy. The dominant recombination channel is a concerted, radiationless decay process that scales as predicted by a simple energy gap law. [ABSTRACT FROM AUTHOR]

Effective patterning of organic semiconductor (OSC) films is an essential prerequisite for large-scale fabrication of organic functional electronics. Although photolithography is a reliable patterning method and is a mature technique, the preparation of microstructured OSC layers with photolithography has been suffering from a sophisticated fabrication procedure. Herein, we demonstrate a robust femtosecond (fs) laser assisted patterning method, which can be effectively used to fabricate microstructured OSC thin films through direct layer ablation of organic materials. Using a well optimized manufacturing procedure, the ablation of both polymeric materials and small molecules is well modulated, and the resulting OSC thin films display typical pore patterns with a feature size less than 2 μm and nearly unaffected charge transport properties. Organic field-effect transistors (OFETs) fabricated on the microstructured OSCs show enhanced gas sensing behavior, with a responsivity to gaseous ammonia ranging from 0.5 to 10 ppm. This work shows that direct laser patterning of organic semiconductors is an effective approach for microstructure fabrication, and highlights the potential application of this method in future organic electronics. [ABSTRACT FROM AUTHOR]