Strategies to design bipolar small molecules for OLEDs: donor-acceptor structure and non-donor-acceptor structure

Toward Self-Driven Autonomous Material and Device Acceleration Platforms (AMADAP) for Emerging Photovoltaics Technologies

ConspectusIn the ever-increasing renewable-energy demand scenario, developing new photovoltaic technologies is important, even in the presence of established terawatt-scale silicon technology. Emerging photovoltaic technologies play a crucial role in diversifying material flows while expanding the photovoltaic product portfolio, thus enhancing security and competitiveness within the solar industry. They also serve as a valuable backup for silicon photovoltaic, providing resilience to the overall energy infrastructure. However, the development of functional solar materials poses intricate multiobjective optimization challenges in a large multidimensional composition and parameter space, in some cases with millions of potential candidates to be explored. Solving it necessitates reproducible, user-independent laboratory work and intelligent preselection of innovative experimental methods.Materials acceleration platforms (MAPs) seamlessly integrate robotic materials synthesis and characterization with AI-driven data analysis and experimental design, positioning them as enabling technologies for the discovery and exploration of new materials. They are proposed to revolutionize materials development away from the Edisonian trial-and-error approaches to ultrashort cycles of experiments with exceptional precision, generating a reliable and highly qualitative data situation that allows training machine learning algorithms with predictive power. MAPs are designed to assist the researcher in multidimensional aspects of materials discovery, such as material synthesis, precursor preparation, sample processing and characterization, and data analysis, and are drawing escalating attention in the field of energy materials. Device acceleration platforms (DAPs), however, are designed to optimize functional films and layer stacks. Unlike MAPs, which focus on material discovery, a central aspect of DAPs is the identification and refinement of ideal processing conditions for a predetermined set of materials. Such platforms prove especially invaluable when dealing with "disordered semiconductors," which depend heavily on the processing parameters that ultimately define the functional properties and functionality of thin film layers. By facilitating the fine-tuning of processing conditions, DAPs contribute significantly to the advancement and optimization of disordered semiconductor devices, such as emerging photovoltaics.In this Account, we review the recent advancements made by our group in automated and autonomous laboratories for advanced material discovery and device optimization with a strong focus on emerging photovoltaics, such as solution-processing perovskite solar cells and organic photovoltaics. We first introduce two MAPs and two DAPs developed in-house: a microwave-assisted high-throughput synthesis platform for the discovery of organic interface materials, a multipurpose robot-based pipetting platform for the synthesis of new semiconductors and the characterization of thin film semiconductor composites, the SPINBOT system, which is a spin-coating DAP with the potential to optimize complex device architectures, and finally, AMANDA, a fully integrated and autonomously operating DAP. Notably, we underscore the utilization of a robot-based high-throughput experimentation technique to address the common optimization challenges encountered in extensive multidimensional composition and parameter spaces pertaining to organic and perovskite photovoltaics materials. Finally, we briefly propose a holistic concept and technology, a self-driven autonomous material and device acceleration platform (AMADAP) laboratory, for autonomous functional solar materials discovery and development. We hope to discover how AMADAP can be further strengthened and universalized with advancing development of hardware and software infrastructures in the future.

A novel donor-acceptor fluorescent probe for the fluorogenic/ chromogenic detection and bioimaging of nitric oxide

Nitric oxide (NO) plays an essential role in regulating various physiological and pathological processes. This has spurred various efforts to develop feasible methods for the detection of NO. Herein we designed and synthesized a novel donor-acceptor fluorescent probe Car-NO for the selective and specific detection of NO. Reaction of Car-NO with NO generated a new donor-acceptor structure with strong intramolecular charge transfer (ICT) effect, and led to remarkable chromogenic change from yellow to blue and dramatic fluorescence quenching. Car-NO exhibited high selectivity, excellent sensitivity, and rapid response for the detection of NO. In addition, the nanoparticles prepared from Car-NO (i.e., Car-NO NPs) showed strong NIR emission and high selectivity/sensitivity. Car-NO NPs was successfully employed to image both endogenous and exogenous NO in HeLa and RAW 264.7 cells. The present findings reveal that Car-NO is a promising probe for the detection and bioimaging of NO.

Comprehensive Characterization of Organic Light-Emitting Materials in Breast Milk by Target and Suspect Screening

Organic light-emitting materials (OLEMs) are emerging contaminants in the environment and have been detected in various environment samples. However, limited information is available regarding their contamination within the human body. Here, we developed a novel QuEChERS (quick, easy, cheap, effective, rugged, and safe) method coupled with triple quadrupole/high-resolution mass spectrometry to determine OLEMs in breast milk samples, employing both target and suspect screening strategies. Our analysis uncovered the presence of seven out of the 39 targeted OLEMs in breast milk samples, comprising five liquid crystal monomers and two OLEMs commonly used in organic light-emitting diode displays. The cumulative concentrations of the seven OLEMs in each breast milk sample ranged from ND to 1.67 × 103 ng/g lipid weight, with a mean and median concentration of 78.76 and 0.71 ng/g lipid weight, respectively, which were higher compared to that of typical organic pollutants such as polychlorinated biphenyls and polybrominated diphenyl ethers. We calculated the estimated daily intake (EDI) rates of OLEMs for infants aged 0-12 months, and the mean EDI rates during lactation were estimated to range from 30.37 to 54.89 ng/kg bw/day. Employing a suspect screening approach, we additionally identified 66 potential OLEMs, and two of them, cholesteryl hydrogen phthalate and cholesteryl benzoate, were further confirmed using pure reference standards. These two substances belong to cholesteric liquid crystal materials and raise concerns about potential endocrine-disrupting effects, as indicated by in silico predictive models. Overall, our present study established a robust method for the identification of OLEMs in breast milk samples, shedding light on their presence in the human body. These findings indicate human exposure to OLEMs that should be further investigated, including their health risks.

Recent synthetic strategies of small heterocyclic organic molecules with optoelectronic applications: a review

Over the past few years, there have been tremendous developments in the design and synthesis of organic optoelectronic materials with appealing applications in device fabrication of organic light-emitting diodes, superconductors, organic lasers, organic field-effect transistors, clean energy-producing organic solar cells, etc. There is an increasing demand for the synthesis of green, highly efficient organic optoelectronic materials to cope with the issue of efficiency roll-off in organic semiconductor-based devices. This review systematically summarized the recent progress in the design and synthesis of small organic molecules having promising optoelectronic properties for their potential applications in optoelectronic devices during the last 10-year range (2010-early 2021).

Rational Design of Bipolar Host and Thermally Activated Delayed Fluorescence Materials in Donor-Acceptor Molecular Architecture: A Theoretical Study

Donor-acceptor (D-A) molecules have drawn massive attention recently in the design of high-performance materials, but the underlying reasons for the magic abilities of D-A architecture in building very different organic semiconductors are still unclear. Here, based on a series of experimentally bipolar host and thermally activated delayed fluorescence (TADF) molecules with the same donor but different acceptor units, it was found that TADF emitters have more effective charge transfer between donor and acceptor units than bipolar host molecules. More efficient conjugation effects between the donor and acceptor units of host materials were identified from the lower dihedral angles of the D-A structure, smaller and even negative charge transfer amount, shorter charge-transfer length, and larger hole-electron overlap extent. These findings with in-depth insights into different interaction models of donor and acceptor units shed important light on the molecular design of TADF emitters and bipolar materials in a D-A architecture.

Azomethine-Containing Pyrrolo[3,2-b]pyrrole Copolymers for Simple and Degradable Conjugated Polymers

Conjugated polymers have received significant attention as potentially lightweight and highly tailorable alternatives to inorganic semiconductors, but their synthesis is often complex, produces toxic byproducts, and they are not typically designed to be degradable or recyclable. These drawbacks necessitate dedicated efforts to discover materials with design motifs that enable targeted and efficient degradation of conjugated polymers. In this vein, the synthetic simplicity of 1,4-dihydropyrrolo[3,2-b]pyrroles (DHPPs) is exploited to access azomethine-containing copolymers via a benign acid-catalyzed polycondensation protocol. Polymerizations involve reacting a dialdehyde-functionalized dihydropyrrolopyrrole with p-phenylenediamine as the comonomer using p-toluenesulfonic acid as a catalyst. The inherent dynamic equilibrium of the azomethine bonds subsequently enabled the degradation of the polymers in solution in the presence of acid. Degradation of the polymers is monitored via NMR, UV-vis absorbance, and fluorescence spectroscopies, and the polymers are shown to be fully degradable. Notably, while absorbance measurements reveal a continued shift to higher energies with extended exposure to acid, fluorescence measurements show a substantial increase in the fluorescence response upon degradation. Results from this study encourage the continued development of environmentally-conscious polymerizations to attain polymeric materials with useful properties while simultaneously creating polymers with structural handles for end-of-life management or/and recyclability.

Synthesis and Properties of Bipolar Ladder-Like Polysiloxane with Carbazole and Triphenylphosphine Oxygen Groups

In this study, a series of ladder-like polysiloxanes are synthesized by introducing double-chain Si-O-Si polymer as the backbone and the carbazole and triphenylphosphine oxide with high triplet energy as side groups. The ladder-like structures of polysiloxanes are achieved through a controlled polymerization method that involves the monomer self-assembly and subsequent surface-restricted solid-phase in situ condensation through freeze-drying. The introduction of siloxane improves thermal stability of the polymers and inhibits the conjugation of the polymers between the side groups, leading to an increase in the triplet energy level. Therefore, all these polymers perform higher triplet energy levels than phosphorescent emitter (FIrpic). The cyclic voltammetry measurements demonstrate that the bipolar polymer exhibits a high highest occupied molecular orbital (HOMO) value of -5.32 eV, which is consistent with the work function of ITO/PEDOT:PSS, consequently facilitating hole injection. Furthermore, the incorporation of triphenylphosphine oxide promotes electron injection. Molecular simulations reveal that the frontier orbital distributions of the bipolar polymer are located on the carbazole and triphenylphosphine groups, respectively, which facilitate the transport of electrons and holes.

Status and Challenges of Blue OLEDs: A Review

Organic light-emitting diodes (OLEDs) have outperformed conventional display technologies in smartphones, smartwatches, tablets, and televisions while gradually growing to cover a sizable fraction of the solid-state lighting industry. Blue emission is a crucial chromatic component for realizing high-quality red, green, blue, and yellow (RGBY) and RGB white display technologies and solid-state lighting sources. For consumer products with desirable lifetimes and efficiency, deep blue emissions with much higher power efficiency and operation time are necessary prerequisites. This article reviews over 700 papers covering various factors, namely, the crucial role of blue emission for full-color displays and solid-state lighting, the performance status of blue OLEDs, and the systematic development of fluorescent, phosphorescent, and thermally activated delayed fluorescence blue emitters. In addition, various challenges concerning deep blue efficiency, lifetime, and approaches to realizing deeper blue emission and higher efficacy for blue OLED devices are also described.

Relating Design and Optoelectronic Properties of 1,4-Dihydropyrrolo[3,2-b]pyrroles Bearing Biphenyl Substituents

Understanding the influence of peripheral functionality on optoelectronic properties of conjugated materials is an important task for the continued development of chromophores for myriad applications. Here, π-extended 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) chromophores with varying electron-donating or electron-withdrawing capabilities were synthesized via Suzuki cross-coupling reactions, and the influence of functionality on optoelectronic properties was elucidated. First, chromophores display distinct differences in the UV-vis absorbance spectra measured via UV-vis absorbance spectroscopy in addition to changes in the onset of oxidation measured with cyclic voltammetry and differential pulse voltammetry. Solution oxidation studies found that variations in the electron-donating and -withdrawing capabilities result in different absorbance profiles of the radical cations that correspond to quantifiably different colors. In addition to fundamental insights into the molecular design of DHPP chromophores and their optoelectronic properties, two chromophores display high-contrast electrochromism, which makes them potentially compelling in electronic devices. Overall, this study represents the ability to fine-tune the optoelectronic properties of DHPP chromophores in their neutral and oxidized states and expands the understanding of structure-property relationships that will guide the continued development of DHPP-based materials.

Integrated System Built for Small-Molecule Semiconductors via High-Throughput Approaches

High-throughput synthesis of solution-processable structurally variable small-molecule semiconductors is both an opportunity and a challenge. A large number of diverse molecules provide a possibility for quick material discovery and machine learning based on experimental data. However, the diversity of the molecular structure leads to the complexity of molecular properties, such as solubility, polarity, and crystallinity, which poses great challenges to solution processing and purification. Here, we first report an integrated system for the high-throughput synthesis, purification, and characterization of molecules with a large variety. Based on the principle "Like dissolves like," we combine theoretical calculations and a robotic platform to accelerate the purification of those molecules. With this platform, a material library containing 125 molecules and their optical-electronic properties was built within a timeframe of weeks. More importantly, the high repeatability of recrystallization we design is a reliable approach to further upgrading and industrial production.

Multifaceted Sulfone-Carbazole-Based D-A-D Materials: A Blue Fluorescent Emitter as a Host for Phosphorescent OLEDs and Triplet-Triplet Annihilation Up-Conversion Electroluminescence

Electroluminescence (EL) from the singlet-excited (S₁) state is the ideal choice for stable, high-performing deep-blue organic light-emitting diodes (OLEDs) owing to the advantages of an adequately short radiative lifetime, improved device durability, and low cost, which are the most important criteria for their commercialization. Herein, we present the design and synthesis of three donor-acceptor-donor (D-A-D)-configured deep-blue fluorescent materials (denoted as TC-1, TC-2, and TC-3) composed of a thioxanthone or diphenyl sulfonyl acceptor and phenyl carbazolyl donor. These systems exhibit strong deep-blue photoluminescence (422-432 nm) in solutions and redshifted emission (472-486 nm) in thin films. The solid-state photoluminescence quantum yield (PLQY) was estimated to be 78 and 94% for TC-2 and TC-3, respectively. TC-2 and TC-3 possess good molecular packing and large molecular cross-sectional areas, which not only improves the PLQY but enhances the triplet-triplet annihilation up-conversion (TTAUC) efficiency of fluorescent emitters. Furthermore, both compounds were applied as an acceptor for confirming their TTAUC property using bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) (Ir(MDQ)₂acac) as the sensitizer. Non-doped OLEDs based on TC-2 and TC-3 exhibit blue EL in the 461-476 nm range. In particular, TC-3 exhibits a maximum external quantum efficiency (EQE_max) of 5.1%, and its EL maximum is 476 nm. In addition, the three emitters were employed as hosts in red OLEDs using bis(1-phenylisoquinoline)(acetylacetonate)iridium(III) (Ir(piq)₂acac) as the phosphorescent dopant. The red phosphorescent OLEDs based on TC-1, TC-2, and TC-3 achieve excellent EQE_max values of 21.6, 22.9, and 21.9%, respectively, and peak luminance efficiencies of 12.0, 14.0, and 12.3 cd A^-1. These results highlight these fluorophores' versatility and promising prospects in practical OLED applications.

Highly Efficient Solution-Processed Blue Phosphorescent Organic Light-Emitting Diodes Based on Co-Dopant and Co-Host System

The low-lying HOMO level of the blue emitter and the interfacial miscibility of organic materials result in inferior hole injection, and long exciton lifetime leads to triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA), so the efficiencies of blue phosphorescent organic light-emitting diodes (PhOLEDs) are still unsatisfactory. Herein, we design co-host and co-dopant structures to improve the efficiency of blue PhOLEDs by means of solution processing. TcTa acts as hole transport ladder due to its high-lying HOMO level, and bipolar mCPPO1 helps to balance carriers’ distribution and weaken TPA. Besides the efficient FIr6, which acts as the dominant blue dopant, FCNIrPic was introduced as the second dopant, whose higher HOMO level accelerates hole injection and high triplet energy facilitates energy transfer. An interesting phenomenon caused by microcavity effect between anode and cathode was observed. With increasing thickness of ETL, peak position of electroluminescence (EL) spectrum red shifts gradually. Once the thickness of ETL exceeded 140 nm, emission peak blue-shifts went back to its original position. Finally, the maximum current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of blue phosphorescent organic light-emitting diode (PhOLED) went up to 20.47 cd/A, 11.96 lm/W, and 11.62%, respectively.

Electrochemical Sulfoxidation of Thiols and Alkyl Halides

Sulfoxides are actively engaged as versatile synthetic building blocks, chiral ligands, bioactive molecules, and function materials. However, their oxidative syntheses from thioethers are inevitably impeded by overoxidation, excess oxidants, and the tedious preparation of thioethers. To address these shortcomings, we report herein a highly selective electrochemical sulfoxidation reaction featuring the use of simple starting materials, i.e., thiols and alkyl halides, in a single operation.

Oligotriarylamine-Extended Organoboranes with Tunable Electron-Donating Strength by Changing the Number of Donor Units

Triarylborane (Ar₃B) and triarylamine (Ar₃N) have been widely employed to construct electronically different donor-acceptor (D-A) systems. Herein, we describe a series of A-D-A-type luminescent organoboranes L-B₂N_n (n = 1, 3, 5) that show an increased number of Ar₃N units as electron donors and two terminal Ar₃B as acceptors. When the Ar₃N moieties were extended from one to five units, their electron-donating strength was gradually enhanced and the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps could also be tuned, which was further reflected in the red-shifted emissions from blue (λ_em = 458 nm) to orange (λ_em = 595 nm) with a decrease in E_gap(elect) from 3.19 to 2.61 eV. L-B₂N₅ showed a huge Stokes shift (∼14 057 cm^-1) and a considerably bright emission with an enhanced solid-state quantum efficiency (Φ_S = 98%) compared with the other members. L-B₂N₃ and L-B₂N₅ exhibited aggregation-induced emissions (AIEs), and an apparent solvatochromic shift was also observed in the emission spectra as the solvent was changed from hexane to tetrahydrofuran (THF) (430 → 595 nm). In addition, the donor-acceptor charge-transfer character in these organoboranes caused a thermally responsive emission over a broad range.

An asymmetric 2,3-fluoranthene imide building block for regioregular semiconductors with aggregation-induced emission properties

For organic semiconductors, the development of electron-deficient building blocks has lagged far behind that of the electron-rich ones. Moreover, it remains a significant challenge to design organic molecules with efficient charge transport and strong solid-state emission simultaneously. Herein, we describe a facile synthetic route toward a new π-acceptor imide building block, namely 2,3-fluoranthene imide, based on which four regioregular small molecules (F1–F4) are synthesized by tuning the imide orientations and the central linkage bridges. All molecules exhibit attractive aggregation-induced emission (AIE) characteristics with strong far-red emission in the powder state, and F3 shows the highest photoluminescence quantum yield of 5.9%. F1 and F3 with a thiophene bridge present an obvious p-type characteristic, while for F3 with an outward imide orientation, the maximum hole mobility from a solution-processed field-effect transistor (FET) device reaches 0.026 cm² V⁻¹ s⁻¹, being ∼10⁴ times higher than the value of F1 with an inward imide orientation. By using a fluorinated thiophene bridge, the resulting F2 and F4 can be turned into n-type semiconductors, showing an electron mobility of ∼1.43 × 10⁻⁴ and ∼3.34 × 10⁻⁵ cm² V⁻¹ s⁻¹, respectively. Our work not only demonstrates that asymmetric 2,3-fluoranthene imide is a promising building block for constructing organic materials with high carrier mobility and strong solid-state emission, but also highlights the importance of regioregular structures in the materials' properties.

A new electron-deficient 2,3-fluoranthene imide unit was easily synthesized through a one-pot reaction for constructing small molecule regioregular semiconductors with good carrier transport ability and strong solid-state emission.

Electrochemical β-chlorosulfoxidation of alkenes

A green and sustainable electrochemical β-chlorosulfoxidation of alkenes with readily available thiols and hydrochloride as the limiting agents has been developed.

Reducing the internal reorganization energy via symmetry controlled π-electron delocalization

The magnitude of the reorganization energy is closely related to the nonradiative relaxation rate, which affects the photoemission quantum efficiency, particularly for the emission with a lower energy gap toward the near IR (NIR) region. In this study, we explore the relationship between the reorganization energy and the molecular geometry, and hence the transition density by computational methods using two popular models of NIR luminescent materials: (1) linearly conjugated cyanine dyes and (2) electron donor–acceptor (D–A) composites with various degrees of charge transfer (CT) character. We find that in some cases, reorganization energies can be significantly reduced to 50% despite slight structural modifications. Detailed analyses indicate that the reflection symmetry plays an important role in linear cyanine systems. As for electron donor–acceptor systems, both the donor strength and the substitution position affect the relative magnitude of reorganization energies. If CT is dominant and creates large spatial separation between HOMO and LUMO density distributions, the reorganization energy is effectively increased due to the large electron density variation between S₀ and S₁ states. Mixing a certain degree of local excitation (LE) with CT in the S₁ state reduces the reorganization energy. The principles proposed in this study are also translated into various pathways of canonically equivalent π-conjugation resonances to represent intramolecular π-delocalization, the concept of which may be applicable, in a facile manner, to improve the emission efficiency especially in the NIR region.

The reorganization energies may be significantly reduced by molecular symmetry effect.

Radical boron migration of allylboronic esters

A photocatalyzed 1,3-boron shift of allylboronic esters is reported. The atom-switch acrobatics proceeds via cascade 1,2-boron migrations and Smiles type rearrangement to furnish a variety of terminally functionalized alkyl boronates.

Design and synthesis of benzothiadiazole-based molecular systems: self-assembly, optical and electronic properties

A comprehensive study was conducted to determine the effect of the donor-group on the solid-state organization and electronic properties of stimuli-responsive benzothiadiazole-based D–A–D building blocks.

Layer-by-Layer Assembly of Monolayer Films Precisely Controlled by LB Technology to Realize Low-Energy Consumption and High-Stability Ternary Data-Storage Devices

Organic semiconductor devices with low energy consumption and excellent stability are highly desirable. Controlling the intermolecular alignment orientation by designing the molecular structure or optimization of the film preparation process is an alternative way to achieve this goal. In this paper, a new idea was proposed to realize the formation of an aligned monomolecular layer and multimolecular layer thin films on the electrode substrate by controlling the surface pressure of molecular layer on the liquid surface by LB technology. An amphiphilic π-conjugated D-A molecule was synthesized, and the influence of spin coating and LB technology on intermolecular ordered stacking in the film and the electrical memory performance were investigated. The results demonstrated that the film fabricated by LB technology has some advantages compared with that fabricated by spin-coating method, such as higher crystallinity, lower surface roughness and better-organized monomolecular and multimolecular layer, which significantly promoted the performance of the electrical memory device with lower power consumption and longer stability.

Tracking Ultrafast Fluorescence Switch-On and Color-Tuned Dynamics in Acceptor-Donor-Acceptor Chromophore

Understanding how the conformational change of conjugated molecules with acceptor-donor-acceptor (A-D-A) architecture affects their physical and optoelectronic properties is critical for determining their ultimate performance in organic electronic devices. Here, we utilized femtosecond transient absorption, time-resolved upconversion photoluminescence spectroscopy, and tunable femtosecond-stimulated Raman spectroscopy, aided by quantum chemical calculations, to systematically investigate the excited state structural dynamics of the intramolecular charge transfer of the tetramethoxy anthracene-based fluorophore 2,3,6,7-tetramethoxy 9,10-dibenzaldehydeanthracene (AnDA) and its derivative 2,3,6,7-tetramethoxy 9,10-diphenylanthracene (TMDPAn) in chloroform. In the AnDA molecule, the tetramethoxy anthracene and benzaldehyde moieties exhibit a strong ability to donate and withdraw electrons. Upon photoexcitation, AnDA shows intriguing ultrafast fluorescence switch-on and red shift dynamics on charge transfer states, and the temporal evolution of AnDA recorded by ultrafast spectroscopy reveals a dynamic picture of two-step intramolecular charge transfer assisted by ultrafast conformational changes and solvation processes. Removing the aldehyde group from TMDPAn significantly decreases the electron pulling capacity of the phenyl unit and disables charge transfer characteristics.

Syntheses and characteristics of push–pull derivatives for quadruply fused porphyrins

“Push–pull” derivatives (2 – 4) of zinc(II) complexes having quadruply fused porphyrinato (QFP) ligands have been synthesized to elucidate the impact of the “push–pull” effects on the electronic structure of QFP. Each ZnQFP derivative of 2 – 4 has an electron-withdrawing group (EWG) such as nitro group and a methoxy group as an electron-donating group (EDG) at the diagonal positions of the molecule. Owing to the extended [Formula: see text]-conjugation of 2– 4 reaching to the substituted positions of the EWG and EDG, charge-transfer (CT) bands, which are sensitive to the solvent polarity, have been observed in the UV-vis spectra. In contrast, the corresponding “push–pull” derivatives of tetraphenylporphyrin, whose [Formula: see text]-conjugation is disconnected at the bonds between the meso-carbon and meso-aryl group, do not exhibit any CT transitions derived from the substituents.

Understanding the role of soft linkers in designing hepatzine-based polymeric frameworks as heterogeneous (photo)catalyst

The emerging class of heptazine-based polymeric materials has shown potential candidature as photocatalyst materials for hydrogen evolution. At the same time, they have shown promising application as solid base materials to catalyse various organic transformations. Thus, the material design rationale needs to be developed around the heptazine-based polymeric frameworks in order to specifically design task specific materials. Herein, we utilised controlled reaction conditions to synthesize the desired polymeric networks with trichloroheptazine as precursor. Material design strategy employed nitrogen rich [tris(2-aminoethylamine) and hydrazine] as soft linkers to understand the effect on band structure of developed heptazine-based polymeric networks. The developed polymeric networks were explored as platform to study systematically the effect on their respective photophysical properties and understand their surface basicity. The framework having aminoalkyl linker showed superior activity in photocatalysis as well as heterogeneous base catalysis. Further, model catalysts revealed the importance of N-atoms as active basic sites in these systems.

The Same Oxidation-State Introduction of Hypervalent Sulfur via Transition-Metal Catalysis

Sulfonyl compounds have attracted considerable interest due to their extensive applications in drug discovery, agricultural, and material science. The access to the assembly of SO₂ -containing compounds via the same oxidative-state introduction of hypervalent sulfur has come to the fore in the recent years. Especially, the transition-metal-involved synthesis of hypervalent sulfur compounds is the most effective strategy since SO₂ is easy to insert into the metal-carbon bonds. This review discusses the application of the same oxidation-state introduction of hypervalent sulfur strategy under the transition-metal-catalyzed conditions, and presents according to different metal catalysts and the synthesized diversity hypervalent sulfur-containing compounds skeletons, including sulfonamides, sulfones, sulfinamides, sulfonyl acids and sulfonyl fluorides.

Tunable electronic and optical properties of a BAs/As heterostructure by vertical strain and external electric field

The CBM (VBM) of the heterostructure is mainly contributed by the BAs (arsenene), which will favor the separation of photogenerated electron–hole pairs.

Photocatalytic three-component annulation enabling stereoselective generation of (Z)-thiochromene 1,1-dioxides

A new photocatalytic three-component annulation of 2-alkynylaryldiazonium tetrafluoroborates with γ-hydroxyl terminal alkynes and sodium metabisulfite is reported and used to produce a series of (Z)-thiochromene 1,1-dioxides.

Revealing Topological Influence of Phenylenediamine Unit on Physicochemical Properties of Donor-Acceptor-Donor-Acceptor Thermally Activated Delayed Fluorescent Macrocycles

A new thermally activated delayed fluorescence (TADF)-displaying macrocyclic compound m-1 comprising of two electron-donors (N,N'-diphenyl-m-phenylenediamine) and two electron-acceptors (dibenzo[a,j]phenazine) has been synthesized. The macrocycle developed herein is regarded as a regioisomer of the previously reported TADF macrocycle p-1, which has two N,N'-diphenyl-p-phenylenediamines as the donors. To understand the influence of the topology of the phenylenediamine donors on physicochemical properties of TADF-active macrocycles, herein the molecular structure in the single crystals, photophysical properties, electrochemical behavior, and TADF properties of m-1 have been investigated compared with those of p-1. The substitution of p-phenylene donor with m-phenylene donor led to distinct positive solvatoluminochromism over the full visible-color range, unique oxidative electropolymerization, and slightly lower contribution of TADF, due to the lower CT character in the excited states.

Golden Age of Fluorenylidene Phosphaalkenes-Synthesis, Structures, and Optical Properties of Heteroaromatic Derivatives and Their Gold Complexes

The substitution of 2,7-dibromo-9-fluorenyl phosphaalkenes with heteroaromatic substituents (bithiophene, benzothiophene, pyridine) offers access to interesting push–pull dye molecules. Steric shielding due to the bulky P-substituent gives marked different reactivities at the 2- and 7-positions, allowing the synthesis of mixed/asymmetric derivatives. Further functionalization via gold(I) coordination was demonstrated and increased the acceptor character, concomitant with a red-shifted absorption.

Complementary amide-based donor-acceptor with unique nano-scale aggregation, fluorescence, and band gap-lowering properties: a WORM memory device

Organic fluorescent semiconducting nanomaterials have gained widespread research interest owing to their potential applications in the arena of high-tech devices. We designed two pyrazaacene-based compounds, their stacked system, and the role of gluing interactions to fabricate nanomaterials, and determined the prospective band gaps utilizing the density functional theory calculation. The two pyrazaacene derivatives containing complementary amide linkages (-CONH and -NHCO) were efficiently synthesized. The synthesized compounds are highly soluble in common organic solvents as well as highly fluorescent and photostable. The heterocycles and their mixture displayed efficient solvent dependent fluorescence in the visible region of the solar spectrum. Notably, the compounds were associated through complementary NH•••O = C type hydrogen bonding, π-π stacking, and hydrophobic interactions, and thereby afforded nanomaterials with a low band gap. Fascinatingly, the fabricated stacked nanomaterial system exhibited resistive switching behavior, leading to the fabrication of an efficient write-once-read-many-times memory device of crossbar structure.

Dual Functionalization of Electron Transport Layer via Tailoring Molecular Structure for High-Performance Perovskite Light-Emitting Diodes

Great progress in modification and optimization of emission layer (EML) in perovskite light-emitting diodes (PeLEDs) results in a significant improvement in device efficiency. However, so far, less attention has been paid to the exploration of hole/electron injection and transporting layers to maximize the utilization of charge carriers for efficient and stable PeLEDs. At present, low electron mobility of electron transport layer (ETL) causes an unbalanced charge injection, and the defects at the ETL/perovskite interface limit the formation and utilization of generated excitons. Here, a series of compounds (BPBiTP, BPBiPN, and BPBiPA) flanked by diphenyl-1H-benzo[d]imidazole end groups have been developed as ETL materials, where the bridging units (benzene, naphthalene, anthracene) are manipulated to achieve dual functionality, namely, the high charge carrier mobility and effective passivation of perovskite surface. The coordinating end groups effectively reduce the trap state at the interface of ETL and EML due to their strong nucleophilic quality. H-aggregation of anthracene units and large transfer integral in BPBiPA lead to its superior electron mobility of 8.4 × 10^-4 cm² V^-1 s^-1 in the solid state, over 1 order of magnitude higher than that of the typical one (TPBi). Consequently, green PeLEDs with a maximum external quantum efficiency (EQE) of 19.7%, reduced efficiency roll-off, as well as extended operational lifetime have been achieved without any outcoupling technique. Our result demonstrated that optimization of ETL materials via improving both passivation capability and electron mobility is a powerful strategy for producing high-performance PeLEDs.

Novel Positive Polaron Stabilizing n-Type Host for High Efficiency and Long Lifetime in Blue Phosphorescent Organic Light-Emitting Diodes

Four electron transport type hosts withstanding the positive polaron stress were synthesized using the benzo[4,5]thieno[3,2-d]pyrimidine core to develop high triplet energy hosts. Four benzo[4,5]thieno[3,2-d]pyrimidine-derived hosts, 4-(9H-carbazol-9-yl)-2-(3-(triphenylsilyl)phenyl)benzo[4,5]thieno[3,2-d]pyrimidine (CzBTPmSi), 2,4-di(9H-carbazol-9-yl)benzo[4,5]thieno[3,2-d]pyrimidine (2CzBTP), 2-(9H-carbazol-9-yl)-4-(3-(triphenylsilyl)phenyl)benzo[4,5]thieno[3,2-d]pyrimidine (mSiBTPCz), and 2,4-bis(3-(triphenylsilyl)phenyl)benzo[4,5]thieno[3,2-d]pyrimidine (2mSiBTP), were designed to have either the tetraphenylsilyl blocking group or the hole transport type carbazole group. The CzBTPmSi and mSiBTPCz were prepared to study the effect of substitution positions of tetraphenylsilyl and carbazole on the device performances, and the 2CzBTP and 2mSiBTP were synthesized as reference materials. In the device application, the four hosts were used as electron transport type hosts mixed with a hole transport type 3,3'-di(9H-carbazol-9-yl)-1,1'-biphenyl (mCBP) host in the mixed host. Among the four mixed hosts, the mCBP/CzBTPmSi mixed host showed an external quantum efficiency of 23.9% and a device lifetime over 4000 h at 100 cd m^-2 in the blue phosphorescent organic light-emitting diodes.

Electronic and Photophysical Properties of 9,10-Anthrylene-Bridged B-π-N Donor-Acceptor Molecules with Solid-State Emission in the Yellow to Red Region

9,10-Anthrylene-bridged triarylborane-triarylamine donor-acceptor compounds were prepared to examine the influence of the bulky π-bridge on the electronic and photophysical properties of the compounds, with the aim of realizing their solid-state emission. The intramolecular charge-transfer (ICT) absorption and emission between the vacant p orbital on the boron center, p(B), and occupied p orbital on the nitrogen center, p(N), through the π orbital of the anthrylene, π(anthrylene), were observed, and it was demonstrated that the HOMO-LUMO gap decreased with increasing number of introduced anthrylene units because of the effective lowering of LUMO originating from the p(B)-π(anthrylene) orbital interaction. The compounds exhibited solid-state emission with emission maxima at 560 nm and 643 nm, respectively, in the yellow to red region, with the corresponding absolute solid-state quantum yield of 18 % and 31 %, as a result of the combination of the highly congested structure originating from the anthrylene π-bridge and the introduction of bulky tert-butyl protecting groups.

Polymorphic mechanoresponsive luminescent material based on a fluorene–phenanthroimidazole hybrid by modulation of intramolecular conformation and intermolecular interaction

This study examined the multiple energetic pathways in solid-state photophysics, which are of increasing importance in solid-state lighting applications.