LUMO Levels Research Articles

PM6/L8‐BO Thin Films through Layer‐by‐Layer Engineering: Formation Mechanism, Energetic Disorder, and Carrier Mobility

ABSTRACTLayer‐by‐layer (LBL) process has emerged as a promising method in the advancement of organic photovoltaics, emphasizing scalability and reproducibility. More importantly, it provides enhanced morphological control for boosting carrier mobility (μ) and power conversion efficiency. By employing a multiscale approach that combined first‐principles calculations, molecular dynamics simulations, and kinetic Monte Carlo methods, the relationship between LBL morphology engineering and carrier mobility in donor/acceptor (PM6/L8‐BO) thin films is elucidated. During solvent evaporation, the order of solid‐phase formation in LBL films was top surface, bottom region, and then the middle region. The early solid precipitation from precursor solutions was acceptor, resulting in a well‐ordered molecular arrangement and reducing energy disorder of acceptor LUMO levels. Furthermore, the difference in energy disorders between the A/D blend region and the pure A or D domains enabled LBL morphology engineering to balance electron and hole mobilities, thereby mitigating charge accumulation and recombination. LBL‐manufactured films presented higher carrier mobility ( = = 1.9 × 10−3 cm2 V−1 s−1) compared to bulk heterojunction (BHJ) films ( > = 0.1 × 10−3 cm2·V−1 s−1). These mechanisms provided insights into strategies for enhancing charge extraction of photo‐generated charge carriers through LBL engineering, driving the development of efficient organic photovoltaic materials.

Study on physical properties of Coronene oxide as a function of number of oxygen atoms and temperature by density functional theory

The electronic properties like (HOMO, LUMO levels and Energy gap), and spectroscopic properties (IR spectra) in addition to thermodynamics characteristics like (Gibbs free Energy, Enthalpy, Entropy, and Heat capacity) of Coronene C24 and reduced Coronene oxide C24Ox where x=1-5 is a number of oxygen atoms and different temperature from (298 – 398) K were studied. The methodology utilized in this study involved the application of Density Functional Theory (DFT) using the Hybrid functional B3LYP (Becke, 3-parameters, Lee –Yang-Parr) with 6-311G** basis sets. The band gap of Coronene (C24) 3.5 eV was calculated, while for reduced coronene oxide C24O - C24O5 has been varied from (1.68 to 0.89) eV due to broken symmetry and adding levels inside the energy gap. The IR intensity of C24O5 increases with increasing temperature between (298 and 398) K because of the number of excited atoms, the spectroscopic properties were compared with experimental results, in particular the Longitudinal Optical (LO) mode of vibration for graphene oxide 1582 cm-1 which agreed well. The Gibbs free energy and enthalpy decreased (in the negative sign) with an increased number of oxygen atoms and temperatures which means an exergonic reaction.

Platinum-Acetylide Complexes as Nonfullerene Acceptors in Organic Photovoltaic Systems.

Three distinct n-type semiconductors were derived from a platinum-trialkyl phosphine complex; to lower their LUMO levels, various indene derivatives were incorporated using thiophene (PtTIC (1)), thieno[3,2-b]thiophene (PtT2IC (2)), and 4H-cyclopenta[2,1-b:3,4-b']dithiophene (PtCDTIC (3)) as the acetylide donor units. Single-crystal X-ray diffractometry analysis revealed translinear platinum-acetylide complexation in all cases. The strong (═O···S) interactions between the oxygen atoms of the indene acceptor units and the sulfur atoms of the thiophene-derived donor units induced a highly planar orientation among the heterocyclic ligands, featuring π-π interactions between the planes. Platinum complexes 1, 2, and 3 exhibited strong absorption in the 500-800 nm range, resulting from efficient intramolecular charge transfer transitions from the central platinum-containing donor unit to the terminal acceptors, as well as unique emission in the near-infrared region owing to the heavy-atom effect. The ultraviolet photoelectron spectroscopy results indicated that the LUMO levels were comparable to those of typical nonfullerene acceptors (NFAs). The n-type semiconductors comprising 1, 2, and 3 as NFAs exhibited photoelectric conversion properties in the corresponding organic photovoltaics. The highest conversion efficiency (3.0%) was attained by complex 3.

Bithiophene-Based Donor-π-Acceptor Compounds Exhibiting Aggregation-Induced Emission as Agents to Detect Hidden Fingerprints and Electrochromic Materials.

A group of bithiophenyl compounds comprising the cyanoacrylate moiety were designed and successfully synthesized. The optical, (spectro)electrochemical, and aggregation-induced emission properties were studied. DFT calculations were used to explain the reaction's regioselectivity and to determine the molecules' energy parameters (i.e., band gaps, HOMO levels, and LUMO levels). The aggregation-induced emission of compounds has been studied in the mixture of DMF (as a good solvent) and water (as a poor solvent), with different water fractions ranging from 0% to 99%. It has been shown that there are differences in the physicochemical properties of the obtained compounds due to the length of the alkyl chain in the ester group. Investigated derivatives were tested for their potential use in visualizing latent fingerprints and electrochromic materials.

Exploring photophysical behavior and fullerene-induced quenching in difluoroboron flavanone [formula omitted]-diketonates for application in organic electronic devices: Experimental and theoretical analysis

The photophysical properties of two difluoroboron flavanone β-diketonates (DK1 and DK2) and their interaction with fullerene (C60) in toluene solution and spin-coated films were investigated using time-correlated single-photon counting, absorption spectroscopy, and steady-state fluorescence spectroscopy. In molecular crystal, the complexes exhibited red-shifted absorption and emission relative to their spectra in solution. Additionally, both complexes displayed bi-exponential decay behavior in time-resolved fluorescence measurements, indicating their capability to form both H and J types of aggregates in the solid state. The introduction of C60 resulted in significant fluorescence quenching and reduced excited-state lifetimes for both complexes. This quenching, observed in both solution and spin-coated films, was primarily driven by photo-induced electron transfer (PET) processes, underscoring the potential of these complexes as donors in fullerene-based heterojunction organic solar cells. To elucidate the process of aggregate formation and the impacts of different dimerization types within the crystalline structure of the complexes, first-principles calculations using Density Functional Theory (DFT) and time-dependent density functional theory (TD-DFT) were performed. We also employed DFT to explore various DK configurations on the fullerene surface, evaluating intermolecular distances and formation energies. These calculations highlighted the energetically favourable gap between the low-lying LUMO levels of the complexes and C60, confirming their suitability for such applications.

Design and synthesis of star-shaped non-fullerene acceptors based on triarylamine core for organic photovoltaic applications

Abstract Non-fullerene acceptors were synthesized with triphenylamine (TPA) and 9-phenylcarbazole core functionalized with oxindole moiety, as well as electron accepting groups such as cyano and trifluoromethyl groups, leading to precisely tuned molecular electronic structures and intermolecular arrangements. This approach maintained high thermal stability and excellent electron mobility while optimizing optoelectronic properties, providing a novel strategy for developing organic photovoltaic materials. LUMO levels of three receptors were comparable to PC61BM. The decomposition temperatures of all three acceptors exceeded 380 °C under N2 flow, indicating the exceptional thermal stability. Notably, the acceptor consisting of TPA core with three oxindole moieties exhibited the red-shifted and intense UV-vis absorption spectrum and the narrowest optical bandgap (Egopt = 2.14 eV). Furthermore, the higher electron mobility was observed in this compound compared to analogues with 9-phenylcarbozle unit. The power conversion efficiency of the device based on TPA core acceptor and regio-regular poly(3-hexylthiophene) surpassed those of the devices based on the other two acceptors.

(Invited) Organic Floating-Gate Transistors for Printable Nonvolatile Memory and Optoelectronic Device Applications

There has been considerable interest in the development of nonvolatile memories using organic materials owing to their potential use in flexible and printed electronic devices. In recent years, organic field-effect transistors (OFETs) having floating-gate structures as the charge storage layer have attracted increasing interest because they allow achieving large threshold voltage (Vth ) shifts and a relatively long retention time with a simple device configuration. However, the fabrication of floating-gate OFET memories by solution processes is generally difficult because it often suffers from the mixing of soluble organic materials at their interfaces. In previous studies, we have developed solution-processable floating-gate OFET memories by using top-gate/bottom-contact OFETs based on polymer semiconductors and the vertical phase separation behavior in the solution-processed composite film of a polymer insulator (PMMA or polystyrene) and a soluble small-molecule semiconductor (TIPS-pentacene) [1-3]. Here, I report the memory characteristics of solution-processed floating-gate OFET memories using a typical p-type polymer semiconductor of polythiophenes (P3HT and PBTTT) and an ambipolar polymer semiconductor based on diketopyrrolopyrrole (DPP) and their usefulness for the development of printable nonvolatile memories and image sensing devices with high functionality.Figure 1(a) shows the typical structure of our memory devices. Since a variety of orthogonal solvents are available for polymer semiconductors, the organic charge storage layer composed of PMMA and TIPS-pentacene molecules can be deposited onto the semiconductor layer by spin coating using butyl acetate. During thermal annealing at 100 ºC, TIPS-pentacene molecules segregate to the upper side of the composite film through vertical phase separation, and floating-gate electrodes consisting of TIPS-pentacene and organic tunneling layers are simultaneously formed by solution processes.Figure 1(b) shows the energy band diagram of the P3HT-based organic FET memory during the programming process. Because P3HT has a shallow LUMO level compared to the work function of the Au source-drain electrodes, the P3HT FET memory shows only a negligible Vth shift when programmed in the dark. Under light illumination, the device exhibits a large Vth shift of over 30 V by storing photogenerated electrons into TIPS-pentacene floating gates. To investigate the applicability of the OFET memories to large-area image sensors, the imaging of a black and white pattern using the recorded drain currents of the memory array under light illumination has been demonstrated [Fig. 1(c)]. We also found that P3HT FET memories with organic semiconductor floating gates exhibit light-intensity dependent synaptic characteristics when programmed under red light, enabling the enhancement of the functionality of organic image sensors.In contrast to OFET memories based on polythiophenes, DPP-DTT FET memories can be programmed in the dark because of the deep LUMO level and good electron transport property of DPP-DTT. It was also found that the electrical characteristics of DPP-DTT TFT memory devices depend on the difference of work function of source-drain and gate electrodes and tuning the energy level difference enables ambipolar carrier trapping and good retention characteristics [Fig. 1(d)]. The DPP-DTT FET memories having hole trapping characteristics also achieve NAND-like memory operations as memory devices are connected in series.

Optical Properties of Disulfiram and Its Metal Complexes Toward the Photoactive Anticancer Effects

Introduction Disulfiram (DSF) has been used for nearly 70 years as an antidrug and is clinically safe. Recently, it has attracted widespread attention, because it was shown through screening to be effective as an anticancer agent. 1) However, further improvement of the efficacy of DSF is required before it can be used as a therapeutic agent. In this study, we focused on metal diethyldithiocarbamate complexes formed by DSF and metal ion (Cu2+, Fe3+), respectively, to improve the efficacy of the drug by applying it to photodynamic therapy. It aimed to enhance the photoresponses of DSF, with Cu complex (DSF-Cu) and Fe complex (DSF-Fe), and to further improve the anticancer effects with the enhanced photoresponses. Methods Cyclic voltammetry (CV) measurements were performed to determine the electrochemical response of each sample and to investigate their redox properties. In addition, electrochemical impedance spectroscopy (EIS) measurements were conducted under both UV light and dark conditions using a carbon plate coated with the samples as the working electrode to investigate the photo-responsiveness of the samples. Methylene blue (MB) degradation tests were then carried out based on JIS R 1703-2: 2014 to assess whether light irradiation of each sample improves the degradation of organic matter. The HOMO-LUMO levels were estimated by photoelectron yield spectroscopy (PYS) measurements and diffuse reflectance spectroscopy. Results and Discussion From CV results, it could be clearly found the oxidation and reduction peaks for DSF, DSF-Cu, and DSF-Fe, indicating that all samples exhibit an electrochemical response. The EIS results also showed that the radius of the capacitive semicircle was reduced by UV irradiation for all samples, which is considered to be due to the decrease in charge transfer resistance as the charge carriers are transferred more efficiently by UV irradiation. The MB degradation test showed a relatively clear MB degradation rate for DSF-Fe (Figure 1). The reason for the difference in MB degradation rates among the samples can be considered to be the difference in reactive oxygen species (ROS) production ability based on the relationship between the HOMO-LUMO gap position and the oxidation/reduction potentials of water and oxygen in each sample. From the estimated HOMO-LUMO level of each sample, it could find that the reduction potential of oxygen (O2/O2 ―: -0.46 V at pH 7) was below the LUMO level in all samples, but the oxidation potential of water (O2/H2O: 0.81 V at pH 7) and the oxidation potential of MB potential (>1.2 V) did not exceed the HOMO level (Figure 2). Therefore, it is possible that MB was oxidatively decomposed by O2 ― produced by the sample's own oxidation and reduction of dissolved oxygen. The difference in the decomposition rate may be due to the difference in the recombination speed of excited electrons. The respective gap energies suggest that DSF-Cu and DSF-Fe can also respond to visible light.[References](1) Yuya Terashima, et al., Nature Communications 11 (609), 2020.(2) S. Trasatti, Pure & Appl Chem. 58 (7), 955-966, 1986. Figure 1

Modifying Intermolecular Interactions of Single-Ion Conducting Polymer Electrolytes through Salt Additives for Stable and High Performance Lithium Metal Batteries

Lithium metal batteries (LMBs) are emerging as a crucial breakthrough in energy storage systems due to their lowest electrochemical redox potential at -3.04V (vs. the standard hydrogen electrode) and highest theoretical capacity of 3860 mAh g-1. However, the irregular deposition on the lithium metal anode during the cycles may lead to the formation of lithium dendrites, adversely affecting the safety and performance of LMBs. Furthermore, concentration polarization can cause lithium depletion at the electrode-electrolyte interface, increasing overpotential and thereby accelerating dendrite growth. Single-ion conducting polymer electrolytes (SIPEs), in which the anion is immobilized, possess the ability to mitigate concentration polarization. Herein, we prepared a salt-in-SIPE (SiSIPE) by incorporating a salt additive (LiTFSI) into SIPEs. Spectroscopy analysis (FT-IR and Raman) and density functional theory (DFT) calculations indicated that NMA, a plasticizer that has crystallinity at 25 ℃, can form a solvation structure with LiTFSI. The intermolecular interactions inhibit the SiSIPE from crystallizing even at -80 ℃, ensure high ionic conductivity (7.0×10-4 S cm-1) at 25 ℃, and lead to a high tLi + (0.67) comparable to that of the SIPE (0.71, 2.2×10-4 S cm-1 at 25℃). Additionally, while NMA is easily decomposed above 4.0 V, the interactions ensure that the SiSIPE possesses a wide electrochemical stability window up to 4.4 V. To suppress the decomposition of the electrolyte and achieve stable cycle performance at high voltage, the electrolyte's HOMO level should be lower than that of the cathode. The DFT calculation results showed that the HOMO level of the solvation structure was found to be lower than when NMA forms hydrogen bonds with each other, which implies that it can suppress the decomposition of NMA at high voltages. Additionally, since the solvation structure has a lower LUMO level than NMA, it is preferentially used for forming the solid electrolyte interphase (SEI) layer. As a result, as shown in the X-ray photoelectron spectroscopy results, due to the salt additive, the SiSIPE forms a more stable SEI layer compared to the SIPE. This leads to improved cycle stability in both Li symmetric cell (0.1 mAh cm-2, 700 hours) and LiFePO4 full cell tests (1 C-rate, 400 cycles, 80% retention). The intermolecular design through the salt additive can not only effectively suppress lithium dendrites but also enhance stability at high voltages and improve the cycle performance of LMBs. These strategies could significantly provide a new perspective in achieving high stability and high-performance LMBs. Figure 1

Comparative theoretical analysis on the adsorption of cationic and anionic on metal iodides in water

This study focused on the comparative analysis of the adsorption of cationic safranine O (SF+) and anionic acid blue 25 (AB−) on (1 1 0) surface of magnesium, manganese, zinc, and nickel metal iodides using DFT and molecular dynamics (MD) simulation. The nature of the interactions has been thoroughly investigated by the HOMO/LUMO energy gap, global reactivity descriptors, Mulliken charge distribution, molecular electrostatic potential (MEP) map, adsorption energy, and natural bond orbital (NBO) analysis. The reactivity of the two dyes was compared based on the LUMO and HOMO energy levels. It was found that SF+ with a LUMO value of −0.991 eV and lower energy gap of 1.184 eV exhibits an electrophilic characteristic and high ability to be strongly adsorbed on the MI2. However, AB− exhibits a higher energy gap of 5.854 eV, indicating its lower reactivity compared to SF+. Mulliken charge distribution of the dyes and their MEP map also showed strongly negative and strongly positive sites. Subsequently, the stabilizing interactions of hyper-conjugation and charge delocalization have been evaluated. In addition, the MD simulation was employed to elucidate the mechanism of the dye’s adsorption on the adsorbent surfaces. The results suggest that the dyes are adsorbed on the four metal iodides in a close parallel position with less adsorption energy for SF+ compared to AB−. Finally, it was found that the Van der Waals forces are predominant in the adsorption process suggesting a physisorption mechanism in accordance with RDF analysis.

A comprehensive investigation of donor-dcceptor anthraquinone derivatives as versatile and efficient photosensitisers for dye-sensitised solar cells

A new metal-free anthraquinone donor–acceptor-π-anchor (D-A-π-A) design was developed using unsymmetrically substituted anthraquinone (ATQ) derivatives functionalized with bromine (Br), diphenylamine (DPA), indoline (Ind), BrATQBzOH, DPAATQBzOH, and IndATQBzOH. The synthesised compounds, functionalized with an anchor group (ethynylbenzoic acid), have been evaluated in practical dye-sensitised solar cell (DSSC) devices to improve electron injection efficiency. Their properties and applicability were analysed and rationalised based on their energy levels and parameters derived from the current–voltage (I-V) curve analysis in real devices. Femtosecond transient absorption measurements of the sensitiser IndATQBzOH with TiO2 revealed distinct excited state dynamics and charge transfer properties, highlighting the influence of the semiconductor interface. In addition, Density Functional Theory (DFT) and Time-Dependent DFT (TDDFT) electronic quantum calculations were performed, which revealed that the new anthraquinone-based dyes exhibit optimal coplanarity for efficient electron transfer, with their LUMO and HOMO energy levels facilitating electron injection into TiO2. In contrast to the low efficiencies found for previously studied anthraquinone derivatives, with maximum photocurrent efficiencies (PCE) below 0.2%, 9,10-anthraquinone derivatives were used as acceptors attached to suitable donors (DPA or Ind), yielding PCE above 1%.

Photovoltaic response promoted via intramolecular charge transfer in triphenylpyridine core with small acceptors: A DFT/TD-DFT study

Currently, A−π−A configured molecules (TTP1-TTP6) were designed from the reference compound (TPPR) by modifying the terminal acceptors for photovoltaic materials. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) using the M06/6-311G(d,p) functional were employed to analyze the photonic and electronic properties of the newly designed derivatives. Various analyses; frontier molecular orbitals (FMOs), density of states (DOS), absorption spectra (λmax), transition density matrix (TDM), binding energy (Eb), hole-electron and open circuit voltage (Voc) were performed to explore the photovoltaic properties of triphenylpyridine based compounds. The structural modulation with acceptor moieties significantly tuned their HOMO and LUMO levels, resulting in reduced band gaps (2.833–3.037 eV). They also exhibited broader absorption spectra (λmax) ranging from 482.560 to 514.756 nm as compared to the reference compound (486.289 nm). Notably, TPP3 showed the good photovoltaic response as it displayed the least energy gap (2.833 eV) with lower binding energy (0.415 eV) and bathochromic shift (512.798 nm) in absorption spectra as compared to all other derivatives. Beside this, a comparative study with spiro-OMeTAD and P3HT standard hole transport materials illustrated that these materials can also be utilized as effective photovoltaic materials.

Engineering π‐Electron Bridge Enables Low‐Potential 2D Redox Polymer Anodes for High‐Voltage Aqueous All‐Organic Batteries

AbstractAqueous all‐organic batteries (AAOBs) have emerged as a hot topic but their development was plagued by limited choices of anode materials, generally facing an intractable trade‐off between low potential and high stability. Here, we propose a novel π‐electron bridge engineering strategy to explore a class of 2D dioxin‐bridged redox covalent organic polymer (RCOP) as trade‐off‐breaking anodes for high‐voltage AAOBs. By establishing a tunable RCOP platform, we perform theoretical study to scrutinize how bridge units between active sites affect the electrode potential and redox activity for the first time. We discover that compared to common pyrazine bridge, the weakened conjugation and strong electron donor character of the proposed dioxin bridge can induce elevated LUMO level and enriched π‐electron populations in active sites, heralding a low electrode potential and enhanced redox activity. Besides, the nonaromaticity‐induced molecular flexibility of dioxin bridge mitigates intermolecular stacking for sufficient active sites exposure. To experimentally corroborate this, a new dioxin‐bridged 2D RCOP (D‐HATN) and its pyrazine‐bridged analogue (P‐HATN) are synthesized for proof‐of‐concept demonstration. D‐HATN displays excellent compatibility with Na+/Zn2+/NH4+/H3O+ and obviously lower redox potentials in various dilute electrolytes compared to P‐HATN and most reported organic anodes, while featuring rapid Grotthuss‐type proton conduction and unprecedented durability in acid – 91.8 % capacity retention after 20000 cycles. Thus, the D‐HATN‐involved all‐organic proton battery delivers an average output voltage of 0.75 V, which can be further elevated to 1.63 V with alkaline‐acidic hybrid electrolyte design, affording markedly‐increased specific energy.

Engineering π-Electron Bridge Enables Low-Potential 2D Redox Polymer Anodes for High-Voltage Aqueous All-Organic Batteries.

Aqueous all-organic batteries (AAOBs) have emerged as a hot topic but their development was plagued by limited choices of anode materials, generally facing an intractable trade-off between low potential and high stability. Here, we propose a novel π-electron bridge engineering strategy to explore a class of 2D dioxin-bridged redox covalent organic polymer (RCOP) as trade-off-breaking anodes for high-voltage AAOBs. By establishing a tunable RCOP platform, we perform theoretical study to scrutinize how bridge units between active sites affect the electrode potential and redox activity for the first time. We discover that compared to common pyrazine bridge, the weakened conjugation and strong electron donor character of the proposed dioxin bridge can induce elevated LUMO level and enriched π-electron populations in active sites, heralding a low electrode potential and enhanced redox activity. Besides, the nonaromaticity-induced molecular flexibility of dioxin bridge mitigates intermolecular stacking for sufficient active sites exposure. To experimentally corroborate this, a new dioxin-bridged 2D RCOP (D-HATN) and its pyrazine-bridged analogue (P-HATN) are synthesized for proof-of-concept demonstration. D-HATN displays excellent compatibility with Na+/Zn2+/NH4 +/H3O+ and obviously lower redox potentials in various dilute electrolytes compared to P-HATN and most reported organic anodes, while featuring rapid Grotthuss-type proton conduction and unprecedented durability in acid - 91.8 % capacity retention after 20000 cycles. Thus, the D-HATN-involved all-organic proton battery delivers an average output voltage of 0.75 V, which can be further elevated to 1.63 V with alkaline-acidic hybrid electrolyte design, affording markedly-increased specific energy.

Visible light-induced degradation of phenolic contaminants utilizing nanoscale TiO2 and ZnO impregnated with SR 7B (SR) dye as advanced photocatalytic systems

ZnO and TiO2 show promise for the remediation of phenol-containing wastewater, but their wide band gaps restrict their industrial-scale application under visible light. However, harnessing visible light in dye-sensitizing systems could significantly enhance their efficacy for industrial purposes. Considering the state-of-the-art, this research represents a pioneering report to explore the development of dye-sensitized photocatalysts using Sudan Red 7B (SR) dye. For this purpose, a new surfactant-capping route was applied to synthesize spherical TiO2 and ZnO nanoparticles. The prepared materials were then impregnated with (SR) dye to produce the unprecedented visible light active dye-sensitized TiO2 (TiO2/SR) with spherical morphology, and sheet form dye-sensitized ZnO (ZnO/SR) photocatalysts. Based on the cyclic voltammetry and UV–Vis results, the LUMO and HOMO energy levels of SR dye were calculated to be −0.8 V and +3.15 V (versus NHE), respectively, providing an adequate thermodynamic driving force for the electron injection processes from dye to conduction bands of TiO2 and ZnO, thus successfully degrading pollutants via the dye-sensitized photocatalytic route. Phenol photodegradation experiments under visible light were conducted using these photocatalysts, applying a diversity of pH and catalyst loading conditions. The results showed that the visible light photocatalytic experiments using TiO2/SR and ZnO/SR had significantly higher performance in degrading phenol, with an output that was almost 5 and 3 times better, respectively, compared to their pure photocatalysts.

Synthesis, optical and electrochemical properties of thiophene and thieno [3, 2-b] thiophene linked with structurally modified rhodanine based copolymers

Thiophene and thieno [3, 2-b] thiophene as an electron rich donor linked with conjugated side chains of 3-octylrhodanine as an acceptor was designed, polymerized via Stille polycondensation route and two copolymers, PTMOT-T (P1) and PTMOT-TT (P2) was obtained. Polymers was completely characterized by different sophisticated instruments (FT-IR, 1HNMR, TGA, GPC, XRD and DFT simulations). Presence of 3-octylrhodanine side chain units was influences the solubility, conformations and electronic properties of resulted polymers. Polymers displayed broad optical absorption, compatible molecular orbitals HOMO and LUMO levels and good thermal stability. Structural features and influence of side chain in PTMOT-T (P1) and PTMOT-TT (P2) was discussed and it could be potential materials for optoelectronic applications. This work showed that the slight modification side chain structure and or side chain engineering is plays a crucial role to tune the structural and optoelectronic properties of desired polymers.

Effects of fluorination of benzothiadiazole units on the properties of alternating cyclopentadithiophene/benzothiadiazole donor/acceptor polymers

AbstractA set of narrow bandgap conjugated polymers was prepared, using cyclopentadithiophene (CDT) donor units coupled with benzothiadiazole (BT) acceptor units substituted with either no fluorine atoms (A1), one fluorine atom (A2) or two fluorine atoms (A3), using the Stille cross coupling reaction. The addition of two electron‐withdrawing fluorine atoms to the BT units was observed to deepen the HOMO energy level of the resulting copolymer, while only slightly affecting the LUMO level, as evidenced by cyclic voltammetry examination. The alternating copolymers (CDT‐A1, CDT‐A2 and CDT‐A3) possess small optical bandgaps of 1.37, 1.43 and 1.51 eV (which should efficiently harvest a broad part of the solar spectrum), and a moderate HOMO level of −5.00, −5.05 and −5.12 eV, respectively. CDT‐A3 displayed the highest optical/electrochemical‐bandgap and the deepest HOMO level, a consequence of the addition of the fluorine atoms on the BT moieties. Inclusion of two fluorine atoms resulted in sharper X‐ray diffraction peaks in the CDT‐A3 copolymer with respect to its analogues CDT‐A1 and CDT‐A2 copolymer indicating a greater crystallinity. These findings clearly demonstrate that fluorination of BT units is an effective approach for adjusting the energy levels and optical properties of BT‐based materials for use in organic solar cells devices as well as for other applications.

Synthesis of Diketopyrrolopyrrole Based Photoactive Materials via Photoredox C−H Activation

AbstractThe synthesis of diketopyrrolopyrrole (DPP) derivatives followed the well‐known conventional cross‐coupling methods such as Suzuki, Stille, Sonogashira, and Negishi cross‐coupling reactions. However, these methods required unfavorable reaction conditions, organometallic precursors, and high temperatures. In addition, the synthesis of conventional cross‐coupling partners including organoboranes, stannane, and acetylenes required drastic reaction conditions and strong bases. In this work, a wide variety of thiophene‐diketopyrrolopyrrole (TDPP)‐based semiconducting materials (36 compounds) were synthesized via Pd‐catalysed photoredox methodology by using N‐hydroxyphthalimide (NHP) based coupling partners, which can be readily prepared from N‐hydroxyphthalimide and carboxylic acid or aldehyde derivatives via single step C−O bond formation reactions with good yield (80–90 %). This methodology minimizes additional synthetic steps, harsh reaction conditions, and high temperature (100–150 °C). Optoelectronic studies suggest that the synthesized materials have suitable band gap, HOMO and LUMO levels for variety of optoelectronic applications. To the best of our knowledge, this is the first report on the synthesis of TDPP‐based π‐conjugated materials via the photoredox method.

Dimesitylborane as Electron Accepting Unit in High Performance Yellow Single-Layer Phosphorescent Organic Light Emitting Diode.

A new host material for Single-Layer Phosphorescent Organic Light-Emitting Diodes (SL-PhOLED) is reported, namely SPA-2-FDMB, using the dimesitylborane (DMB) fragment as an acceptor unit. The molecular design is constructed on the general donor-spiro-acceptor architecture, which consists of connecting, via a spiro bridge, a donor and an acceptor units in order to avoid strong interaction between them. The DMB fragment is known for many electronic applications (notably Aggregation-Induced Emission) but has not been used yet for SL-PhOLED applications. This appears particularly interesting, as the development of this simplified technology has shown that only a few electron-accepting fragments such as diphenylphosphine oxide can provide high-performance devices. Herein, the yellow-emitting SL-PhOLED using SPA-2-FDMB as host presents an External Quantum Efficiency of 8.1% (Current Efficiency of 24.9cd.A-1) with a low threshold voltage of 2.6V. As SPA-2-FDMB presents a sharp HOMO/LUMO difference, the good matching of HOMO and LUMO energy levels with the Fermi level of the electrodes is responsible for these performances. The low LUMO level of -2.61eV also appears particularly important. These performances are, to date, the highest reported for a yellow/orange-emitting SL-PhOLED and show the potential of DMB unit in the single-layer technology.

Amplifying the photovoltaic properties of tetrathiafulvalenes based materials by incorporation of small acceptors: a density functional theory approach

Currently, polycyclic aromatic compounds in organic solar cells (OSCs) have gained substantial consideration in research communities due to their promising characteristics. Herein, polycyclic aromatic hydrocarbons (PAHs) core-based chromophores (TTFD1-TTFD6) were designed by structural modifications of peripheral acceptor groups into TTFR. The density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were carried out at B3LYP/6-311G (d, p) functional to explore insights for their structural, electronic, and photonic characteristics. The structural modulation unveiled notable electronic impact on the HOMO and LUMO levels across all derivatives, leading to decreased band gaps. All the designed compounds exhibited band gap ranging from 2.246 to 1.957 eV, along with wide absorption spectra of 897.071-492.274 nm. An elevated exciton dissociation rate was observed due to the lower binding energy values (Eb = 0.381 to 0.365 eV) calculated in the derivatives compared to the reference (Eb = 0.394 eV). Furthermore, data from the transition density matrix (TDM) and density of states (DOS) also corroborated the effective charge transfer process. Comparable results of Voc for reference and designed chromophores were obtained via HOMOdonor−LUMOPC71BM. The declining Voc order values was noted as TTFD5 > TTFD6 > TTFD4 > TTFD3 > TTFD2 > TTFD1 > TTFR. Interestingly, TTFD5 was found with the smallest energy gap and highest absorption value, resulting in better charge transference among all the derivatives. The results illustrated that the modification in indenofluorene based chromophores with end-capped small acceptors proved to be a significant approach in achieving favorable photovoltaic properties.