Donor Acceptor Research Articles

One- and Two-Photon Photophysical Properties, Ultrafast Dynamics, and DFT Study of Three Modified Zinc Phthalocyanines.

As two-photon absorption (TPA) materials, phthalocyanine molecules have promising application prospects due to their large TPA absorption cross-section, high third-order nonlinear optical susceptibility, and ultrafast response characteristics. In this work, optical properties and the ultrafast response of three modified zinc phthalocyanine molecules (P-HPcZn, Pc-P-Pc, and (DR1)4PcZn) were analyzed. No obvious side-shoulder absorption peaks in the Q-band can be observed from the steady-state absorption spectra of the three molecules, confirming the lack of aggregation products in the solutions of our measurement. Open-aperture Z-scan results show relatively large TPA cross-section values of 136.4 and 55.3 GM for Pc-P-Pc and (DR1)4PcZn, respectively. The nonlinear optical results show that the absorption process observed under the excitation of femtosecond pulses is a reverse saturable absorption (RSA) mechanism. Up-conversion fluorescence spectra of (DR1)4PcZn in THF solution indicate that the fluorescence emission mechanism is TPA. In the study of ultrafast dynamics, the transient absorption spectra were investigated and the decay lifetime of the dynamic traces corresponding to some representative probe wavelengths was obtained through data fitting with a multi-exponential function. Finally, the charge transfer and excited state properties of the modified zinc phthalocyanine molecules were discussed in depth by the DFT method. The energy gaps of P-HPcZn, Pc-P-Pc, and (DR1)4PcZn are 2.16, 1.39, and 2.13 eV, respectively. The results indicate that the Pc-P-Pc of donor-acceptor-donor (D-A-D) structure has the smallest energy gap as well as the best charge transfer properties.

Balancing TADF Properties in π-Bridged Donor–Acceptor Systems by Sterical Constraints: The Best of Three Worlds

Balancing TADF Properties in π-Bridged Donor–Acceptor Systems by Sterical Constraints: The Best of Three Worlds

Compatibilizer Effects of Strategically Designed Donor–Acceptor Block Copolymers to Enhance the Performance, Stability, and Mechanical Durability of Inverted Organic Solar Cells

AbstractA strategically designed donor–acceptor (D‐A) block copolymer (PM6‐b‐PYIT) is introduced, as a compatibilizer to enhance the performance and stability of inverted organic solar cells (OSCs) consisting of a bulk heterojunction (BHJ) of PM6 and L8‐BO. The PM6‐b‐PYIT compatibilizer not only significantly boosts the power conversion efficiency from 16.32% to 18.02%, but also further modulates the molecular arrangement and improves the compatibility between donor and acceptor materials. This stems from the structural similarity between the copolymer and the host materials, which facilitates ordered molecular stacking and superior charge‐transporting properties, thereby improving the dielectric constant and built‐in voltage and mitigating excessive charge recombination. More importantly, the role of the compatibilizer in stabilizing the BHJ morphology under long‐term aging conditions is highlighted, ascribed to the improved miscibility between different components in the BHJ composite. This in turn renders the photoactive layer more mechanically durable, making it suitable for stretchable applications.

Photoactive Donor–Acceptor Covalent Organic Framework Material for Synergistic Cyclization Approach to Imidazole Derivatives

ABSTRACTAs one of the most potential platforms for heterogeneous catalysis, two‐dimensional porphyrin‐based covalent organic frameworks (COFs) have attracted great research interests. In this work, following the correlation of COF structure and their performance, a type of donor–acceptor 2D COF (Por‐COF‐Zn) based on porphyrin and thiophene units was designed and easily constructed by one‐pot method using 5,10,15,20‐tetra‐(4‐aminophenyl)porphyrin (TAPP), thieno[3,2‐b]thiophene‐2,5‐dicarbaldehyde, and zinc acetate. The as‐synthesized COF material is tested to show high crystallinity and good thermal and chemical stability. The Brunauer–Emmett–Teller (BET) measure results show that the specific surface area of Por‐COF‐Zn is 413.6 m2g−1, and the pore volume is 0.279 cm3g−1. Transient photocurrent response and EIS measurement also demonstrate that Por‐COF‐Zn exhibits an efficient separation of photogenerated electron/hole pairs. The photocatalytic performance of the resulted COF was further evaluated by using intramolecular cyclization of N‐phenyl‐o‐phenylenediamine and benzaldehyde to form benzimidazole derivative. The catalyst system exhibited good to high conversion efficiency, moderate substrate applicability, and excellent stability and recyclability for the catalytic cyclization approach of benzimidazoles. The catalytic mechanism should be contributed to the synergistic effect of organic framework and metallic zinc. Our current work also provides valuable information for understanding COF‐based photocatalytic systems and further highlight new insights to meet new challenges of heterogeneous photocatalysis.

Excited-State Symmetry Breaking and Localization in a Noncentrosymmetric Electron Donor-Acceptor-Donor Molecule.

Electronic excitation in quadrupolar conjugated molecules rapidly localizes on a single electron donor-acceptor (DA) branch when in polar environments. The loss of center of inversion upon this excited-state symmetry breaking (ES-SB) can be monitored by exploiting the relaxation of the exclusion rules for IR and Raman vibrational transitions. Here, we compare ES-SB in a right-angled (1) and a centrosymmetric (2) DAD dyes using time-resolved IR spectroscopy. We show that the localization of the excitation can also be identified with the bent molecule 1. We find that contrary to dye 2, subpopulations with localized and delocalized excitation coexist for 1 in weak to medium polar solvents. This difference originates from the torsional disorder present in the excited state of 1 but not of 2. Additionally, irreversible localization in a bent molecule is shown to require higher solvent polarity than in a centrosymmetric one.

Dihedral Angles and Photoluminescence Quantum Yields: An NMR Analysis.

The synthesis of two different series of donor-acceptor (D-A) molecules is reported, consisting of a series of four structurally related donors and two different acceptors. The subtle differences in the electron density of these D-A-D and D-A compounds are clearly reflected in the different chemical shifts of certain donor protons in the 1H NMR spectra. These shifts show a cosine squared correlation of the dihedral angle between the donor units and the neighbouring phenyl unit of the acceptor. This correlation is also related to optical properties such as the photoluminescence quantum yield, which shows a similar trend due to the different degree of charge transfer during excitation and relaxation processes. In this way, it is possible to directly correlate a molecular structural parameter with a material property on a purely experimental basis, which should be applicable to many donor-acceptor systems.

Toward rapid and efficient protocols: Synthesis of benzotriazole-based π-conjugated polymers via direct arylation polycondensation under aerobic conditions

π-Conjugated polymers (CPs) are widely used in the field of high-performance plastic electronics. However, the development of sustainable and efficient methods for synthesizing donor-acceptor (D–A)-type CPs remains challenging for their industrialization. In this study, we introduce a simple and rapid direct arylation polycondensation (DArP) technique for preparing various D–A benzotriazole-based π-CPs with high molecular weights under aerobic conditions in two hours. Additionally, the method demonstrates not only excellent yields but also copolymers with nearly defect-free structures. Via a minor modification involving the use of twenty or more equivalents of the base K2CO3 and refluxing the solvent, high molecular weight copolymers can be achieved in a short reaction time under oxygen and moisture conditions. Therefore, this finding presents a direct synthetic protocol that utilizes commercially available and air-stable catalyst precursors to produce high-quality π-CPs suitable for optoelectronic applications.

Role of electron withdrawing moieties in phenoxazine–oxadiazole-based donor–acceptor compounds towards enriching TADF emission

Herein, we reported the effect of electron withdrawing units, such as trifluoromethyl (CF3) and cyanide (CN), substitution on a thermally activated delayed fluorescent (TADF) molecule (10-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)-10H-phenoxazine (PXZ-OXD)). The addition of electron withdrawing units has increased the acceptor strength and reduced the interaction between PXZ and OXD, thus reducing the gap between the singlet and triplet states (ΔEST) of excitons. To understand the variation in the acceptor strength of PXZ-OXD as a function of its molecular structure and density of states, density functional theory (DFT) and time-dependent DFT (TDDFT) were conducted. Transition density matrix investigations revealed that the addition of −CF3 and –CN to PXZ-OXD triggers CT excitons, while inducing lower ΔEST values. Particularly, the lowest ΔEST (0.05 eV) with a notable red shift in the emission spectrum was observed with 4′-CF3PXZOXD. The delayed component lifetime of PXZOXD is found to be reduced after the substitution of −CNwhm and −CF3. Despite the weak charge transfer transitions, the substitution of conjugative –CN group is found to be beneficial in improving the HOMO-LUMO overlap with a moderate decrease in reverse intersystem crossing (KRISC), which attained enhancement in the photoluminescent quantum yield. Additionally, the substitution of the above electron withdrawing units on PXZ-OXD yielded a red shift in the electroluminescence spectrum. Furthermore, the external quantum efficiency (at 100 cd/m2, i.e., EQE100) of the 4′-CNPXZOXD-based organic light-emitting diode is found to improve by 21.13 % against the PXZOXD (16.9 %).

Beyond SM315: A Comprehensive Analysis of Power Conversion Efficiency in Tailored Donor–Acceptor Porphyrin Sensitizers for DSSCs

Beyond SM315: A Comprehensive Analysis of Power Conversion Efficiency in Tailored Donor–Acceptor Porphyrin Sensitizers for DSSCs

Enhanced electrical properties and Vickers hardness of calcium bismuth niobate ceramics by W/Co substituted at B-site

Calcium bismuth niobate (CBN) ceramic, as a core element of high-temperature piezoelectric sensors, has attracted widespread attention due to its high Curie temperature within the class of Aurivillius compounds. However, CBN usually faces two shortcomings: poor piezoelectric constant and low resistivity. In this work, CBN-based ceramics with donor–acceptor ions (W/Co) co-substituted at B-site were prepared by solid-state reaction method, and structure–property relationship of ceramics was studied in detail. Co-substitution of W/Co ions effectively improved the electrical property and hardness of CBN ceramics. CaBi2Nb[Formula: see text](W[Formula: see text]Co[Formula: see text]O9 exhibits enhanced electrical and mechanical properties including high resistivity of [Formula: see text]cm at 500°C, piezoelectric constant of [Formula: see text] pC/N and hardness value of [Formula: see text][Formula: see text]GPa. These values are two orders of magnitude, over two times, and 1.36 times higher than those of pure CBN ceramic, respectively. This work provides a reference for exploring other bismuth-layered structural ceramics.

Photophysical properties of donor–acceptor antiaromatic organoboron compounds based on dithienodiborinines

Abstract Boron-containing antiaromatics, such as diborinines and boroles, have sparked interest in materials chemists owing to their exciting optical properties and high Lewis acidity. In this study, we synthesized donor–acceptor (D–A) type diborinines fused with thiophene rings by introducing electron-donating amino-substituted aryl groups onto boron and elucidated their properties. The D–A type dithienodiborinines exhibited long-wavelength absorption arising from their D–A interactions and antiaromaticity. In addition, their fluorescence intensity increased under oxygen-free conditions, indicating thermally activated delayed fluorescence.

Efficient Molecular Array Control and Vapochromic Behavior Changes by Positional Isomer‐Dependent Molecular Building Blocks

AbstractStructurally flexible organic porous molecular arrays are promising for the development of vapochromic materials with superior detection performance. Exploring the photophysical control of vapochromic materials using these molecular arrays is important for the design of new vapochromic materials. However, difficulties arise in the formation and control of organic porous molecular arrays owing to weak and less‐oriented noncovalent forces and their tendency to arrange into energetically preferred high‐density configurations. Herein, an efficient strategy is presented to control molecular arrays by manipulating the shapes of donor–acceptor–donor system‐based molecular building blocks using positional isomerism and report on the correlation between controlled molecular arrays and vapochromic behavior. Depending on their shape (Z‐shaped, quasi‐Z‐shaped, or linear shape), the building blocks formed different molecular arrays that controlled the intermolecular interactions and void volumes. This led to differences in the final microstructural morphologies. Consequently, they exhibited different vapochromic behaviors, and an in‐depth understanding of the correlation between the molecular arrays and vapochromism/vapofluorochromism is obtained.

Integrated Cyano Groups into the Skeleton of Conjugated Polymers to Activate Molecular Oxygen for Boosting Photocatalytic H2O2 Efficiency.

Conjugated polymers (CPs) have shown promising potential in the field of hydrogen peroxide (H2O2) photosynthesis. However, a deeper understanding of the interactions between building units and specific functional groups within the molecular skeleton is necessary to elucidate the mechanisms driving H2O2 generation. Herein, a series of typical donor-acceptor (D-A) conjugated polymers (B-B, B-CN, B-DCN) were synthesized by introducing different amounts of cyano groups (-CN) into the molecular skeleton. The strong electron withdrawing properties of cyano can greatly promote the effective separation and transfer of photogenerated charges between building units, resulting in an impressive efficiency of H2O2 generation (2128.5 μmol g-1 h-1) for B-DCN, representing a 96-fold enhancement compared to B-B. More importantly, experimental results and theoretical calculations further revealed that the introduction of -CN can markedly reduce the adsorption energy (Ead) of O2, while serving as an active site to induce the conversion of crucial intermediate superoxide anions (.O2-) into singlet oxygen (1O2), achieving dual-channel H2O2 generation (O2→.O2-→H2O2, O2→.O2-→1O2→H2O2). This work provides valuable insights into the design of efficient H2O2 photosynthesis materials.

Facile Synthesis of Donor-Acceptor Heterocycloarenes Based on Pyrazine Derivatives Possessing Intriguing Iodide Ion Capture Properties.

Donor-acceptor (D-A) conjugated systems have been extensively investigated and play important roles in organic electronics. Incorporating D-A structures into (hetero)cycloarenes endows them tunable electronic properties, while the well-defined cavity remains. However, the synthetic complexity of introducing electron-acceptor moieties into (hetero)cycloarenes limits their development and applications. In this paper, the first family of electronically tunable D-A heterocycloarenes (DAHCn, n = 1-5) based on pyrazine derivatives was facilely synthesized through cyclocondensation reaction from a tetraketone-functionalized heterocycloarene precursor prepared using the ketal-protection strategy. The effect of expanded conjugation and the inserted electron-withdrawing group on the electronic structures of the D-A heterocycloarenes was studied systematically by X-ray crystallographic analysis, various spectroscopic measurements, and theoretical calculations. Interestingly, the presence of an electron-withdrawing group polarizes the inner C(sp2)-H and significantly increases the binding affinities of D-A heterocycloarenes to the iodide anion. Meanwhile, the anion affinity can be further modulated by the type of attached substituents and the distance of polarization. More importantly, the dicyanopyrazine derivative DAHC3 shows the highest binding strength to the iodide ion as a 2:1 sandwich complex (log β2 = 12.3 and ΔG = -69.1 kJ mol-1), which is the strongest iodide receptor using C(sp2)-H hydrogen bonding interactions reported to date. Our finding provides a new strategy to design and synthesize D-A heterocycloarenes and strong anion receptors.

Improving Miscibility of Polymer Donor and Polymer Acceptor by Reducing Chain Entanglement for Realizing 18.64 % Efficiency All Polymer Solar Cells.

All-polymer solar cells have experienced rapid development in recent years by the emergence of polymerized small molecular acceptors (PSMAs). However, the strong chain entanglements of polymer donors (PDs) and polymer acceptors (PAs) decrease the miscibility of the resulting polymer mixtures, making it challenging to optimize the blend morphology. Herein, we designed three PAs, namely PBTPICm-BDD, PBTPICγ-BDD and PBTPICF-BDD, by smartly using a BDD unit as the polymerized unit to copolymerize with different Y-typed non-fullerene small molecular acceptors (NF-SMAs), thus achieving a certain degree of distortion and giving the polymer system enough internal space to reduce the entanglements of the polymer chains. Such effects increase the chances of the PD being interspersed into the acceptor material, which improve the solubility between the PD and PA. The PBTPICγ-BDD and PBTPICF-BDD displayed better miscibility with PBQx-TCl, leading to a well optimized morphology. As a result, high power conversion efficiencies (PCEs) of 17.50 % and 17.17 % were achieved for PBQx-TCl : PBTPICγ-BDD and PBQx-TCl : PBTPICF-BDD devices, respectively. With the addition of PYFT-o as the third component into PBQx-TCl : PBTPICγ-BDD blend to further extend the absorption spectral coverage and finely tune microstructures of the blend morphology, a remarkable PCE of 18.64 % was realized finally.

Improving Miscibility of Polymer Donor and Polymer Acceptor by Reducing Chain Entanglement for Realizing 18.64 % Efficiency All Polymer Solar Cells

AbstractAll‐polymer solar cells have experienced rapid development in recent years by the emergence of polymerized small molecular acceptors (PSMAs). However, the strong chain entanglements of polymer donors (PDs) and polymer acceptors (PAs) decrease the miscibility of the resulting polymer mixtures, making it challenging to optimize the blend morphology. Herein, we designed three PAs, namely PBTPICm‐BDD, PBTPICγ‐BDD and PBTPICF‐BDD, by smartly using a BDD unit as the polymerized unit to copolymerize with different Y‐typed non‐fullerene small molecular acceptors (NF‐SMAs), thus achieving a certain degree of distortion and giving the polymer system enough internal space to reduce the entanglements of the polymer chains. Such effects increase the chances of the PD being interspersed into the acceptor material, which improve the solubility between the PD and PA. The PBTPICγ‐BDD and PBTPICF‐BDD displayed better miscibility with PBQx‐TCl, leading to a well optimized morphology. As a result, high power conversion efficiencies (PCEs) of 17.50 % and 17.17 % were achieved for PBQx‐TCl : PBTPICγ‐BDD and PBQx‐TCl : PBTPICF‐BDD devices, respectively. With the addition of PYFT‐o as the third component into PBQx‐TCl : PBTPICγ‐BDD blend to further extend the absorption spectral coverage and finely tune microstructures of the blend morphology, a remarkable PCE of 18.64 % was realized finally.

BF2‐Bridged Azafulvene Dimer‐Based 1064 nm Laser‐Driven Superior Photothermal Agent for Deep‐Seated Tumor Therapy

AbstractSmall organic photothermal agents (PTAs) with absorption bands located in the second near‐infrared (NIR‐II, 1000–1700 nm) window are highly desirable for effectively combating deep‐seated tumors. However, the rarely reported NIR‐II absorbing PTAs still suffer from a low molar extinction coefficient (MEC, ϵ), inadequate chemostability and photostability, as well as the high light power density required during the therapeutic process. Herein, we developed a series of boron difluoride bridged azafulvene dimer acceptor‐integrated small organic PTAs. The B‐N coordination bonds in the π‐conjugated azafulvene dimer backbone endow it the strong electron‐withdrawing ability, facilitating the vigorous donor‐acceptor‐donor (D‐A‐D) structure PTAs with NIR‐II absorption. Notably, the PTA namely OTTBF shows high MEC (7.21×104 M−1 cm−1), ultrahigh chemo‐ and photo‐stability. After encapsulated into water‐dispersible nanoparticles, OTTBF NPs can achieve remarkable photothermal conversion effect under 1064 nm irradiation with a light density as low as 0.7 W cm−2, which is the lowest reported NIR‐II light power used in PTT process as we know. Furthermore, OTTBF NPs have been successfully applied for in vitro and in vivo deep‐seated cancer treatments under 1064 nm laser. This study provides an insight into the future exploration of versatile D‐A‐D structured NIR‐II absorption organic PTAs for biomedical applications.

BF2-Bridged Azafulvene Dimer-Based 1064 nm Laser-Driven Superior Photothermal Agent for Deep-Seated Tumor Therapy.

Small organic photothermal agents (PTAs) with absorption bands located in the second near-infrared (NIR-II, 1000-1700 nm) window are highly desirable for effectively combating deep-seated tumors. However, the rarely reported NIR-II absorbing PTAs still suffer from a low molar extinction coefficient (MEC, ϵ), inadequate chemostability and photostability, as well as the high light power density required during the therapeutic process. Herein, we developed a series of boron difluoride bridged azafulvene dimer acceptor-integrated small organic PTAs. The B-N coordination bonds in the π-conjugated azafulvene dimer backbone endow it the strong electron-withdrawing ability, facilitating the vigorous donor-acceptor-donor (D-A-D) structure PTAs with NIR-II absorption. Notably, the PTA namely OTTBF shows high MEC (7.21×104 M-1 cm-1), ultrahigh chemo- and photo-stability. After encapsulated into water-dispersible nanoparticles, OTTBF NPs can achieve remarkable photothermal conversion effect under 1064 nm irradiation with a light density as low as 0.7 W cm-2, which is the lowest reported NIR-II light power used in PTT process as we know. Furthermore, OTTBF NPs have been successfully applied for in vitro and in vivo deep-seated cancer treatments under 1064 nm laser. This study provides an insight into the future exploration of versatile D-A-D structured NIR-II absorption organic PTAs for biomedical applications.

Room temperature phosphorescence materials based on small organic molecules: Design strategies and applications

AbstractRoom‐temperature phosphorescence (RTP) materials have attracted significant attention due to their applications in various fields such as information storage and encryption, organic light‐emitting diode (OLED), sensing, lighting and display, biological imaging, and photodynamic therapy. Traditionally, RTP materials can be efficiently developed using inorganic systems with noble metals or rare earth elements. Recently, many efforts have been devoted to the development of RTP materials based on small organic molecules. The strategies to construct RTP materials include hydrogen bonding, heavy atom effect, n–π* transitions, π–π stacking, donor–acceptor effect, and host–guest doping. Herein, we summarize the recent examples of RTP materials based on small organic molecules primarily focusing on their design strategies and properties. Moreover, their promising applications in information encryption, OLED, as well as bio‐imaging and phototherapy are discussed. The challenges and perspectives are given to provide inspiration toward the future development of organic RTP materials.

Electron Donor–Acceptor Activated Single Atomic Sites for Boosting Oxygen Reduction Reaction

AbstractFabricating efficient non‐platinum‐group‐metal catalysts for the oxygen reduction reaction (ORR) in proton‐exchange membrane fuel cells still remains a big challenge. This study creates a unique bamboo‐like architecture of Mn and Fe single atomic sites (SASs) anchored on core‐shell structure of nanopaticles@carbon nanotubes (MnFe SASs/NPs@CNTs) via a precursor route, where the Fe nanoparticles (NPs) (identified as γ‐Fe and Austenite) are confined into CNTs, such an architecture exhibits compelling ORR activity and durability in 0.1 m HClO4. Experiments and calculations both reveal that the electron donor–acceptor paradigm between Mn SASs and Fe NPs launches a lattice‐electron coupling mechanism not only increasing occupation of π‐antibonding orbital in Mn−*O intermediates but also rising Jahn–Teller effect, thereby destabilize the Mn−*O intermediate and eventually facilitate the potential‐limiting step from *O to *OH. Such a coupling activation of the ORR‐inert Mn SASs greatly improves ORR performances of MnFe SASs/NPs@CNTs.