Donor Acceptor Research Articles

Alkyl chain regulation of charge separation efficiency in edge-grafted g-C3N4 with carboxyl-alkyl substituted polythiophene for enhanced 2-mercaptobenzothiazole photodegradation

To investigate the effect of alkyl chain on the charge separation of photocatalyst, three mono-component edge-grafted g-C3N4 with carboxyl-substituted polythiophenes (CN-CSPs) were designed and synthesized, which chemically anchored polythiophenes to the edge of g-C3N4 framework by amide bond. Theoretical calculations reveal that the donor-acceptor (D-A) structure of the CN-CSPs positions the HOMO at the CSP donor and the LUMO at the heptazine ring acceptor, effectively enhancing intramolecular charge separation. Moreover, the alkyl chain connecting thiophene units to carboxyl groups significantly alters the electronegativity of the carboxyl groups, thereby influencing the dipole moment (DM). An increase in DM correlates with stronger intramolecular charge separation. The DM values of the CN-CSPs rank in the following order: CN-Me(5) (without alkyl) < CN-Et(3) (linear alkyl) < CN-Ma(3) (branched alkyl), consistent with the increasing order of their photocatalytic performance. This modification led to a 17-fold increase in the photocatalytic degradation of 2-mercaptobenzothiazole by the modified CN-Ma(3) compared to pure CN, demonstrating significant cyclic stability and overall enhanced performance of the photocatalytic system. The insights from this study offer valuable guidance for the chemical modification of g-C3N4 to boost photocatalytic efficiency.

Visible light induced reactions of quinones

AbstractThis review covers the visible light induced reactions of quinones such as benzoquinone, naphthoquinone, and anthraquinone. These quinones are distinguished by their fully conjugated structures, which feature minimal energy gaps, and nonbonding electron pairs on the oxygen atoms. Such structural attributes facilitate np → π* transition, allowing for easy access to excited states and rendering quinones highly reactive under visible‐light irradiation. We describe three primary types of reactions facilitated by these electronic characteristics: Paternò–Büchi (PB) reactions, which entail [2 + 2] photocycloaddition between the carbonyl groups of quinones and alkenes or alkynes; CH activation processes, which showcase quinones' versatility in functionalizing hydrocarbons; and the formation of electron donor–acceptor complexes, demonstrating quinones' capability to engage in charge transfer interactions. Through this review, we highlight the critical role quinones play in photochemistry, their unique electronic properties, and their broad applicability in synthetic organic chemistry.

Isoreticular Squaraine-Linked Titanium-Organic Frameworks for Photocatalytic Water Splitting to Hydrogen Under Visible Light.

Inspired by the excellent photocatalytic activity of TiO2, titanium metal-organic frameworks (Ti-MOFs) with broad absorption of visible light are regarded as promising photocatalysts, but carboxylate-linkers used in them are mainly limited to the large extended π-electron systems. Developing Ti-MOFs using organic linkers with a donor-acceptor-donor (D-A-D) structure is expected to improve their charge separation but is still challenging. Herein the design of two new isoreticular Ti-MOFs, Ti6-SQ1 and Ti6-SQ2 are reported, by using squaraines bearing different electron donors as organic linkers. Discrete fourier transform (DFT) calculations demonstrate that ligand-to-metal charge transfer (LMCT) from the acceptor units of squaraines to the Ti6-oxo secondary building units (SBUs) drives the photocatalytic water splitting to hydrogen reaction. Compared with Ti6-SQ2, the shorter distance between the squaraine centers and the Ti6-oxo SBUs in Ti6-SQ1 makes stronger LMCT, showing higher photocatalytic hydrogen evolution efficiency of 11.5mmol g-1h-1 under visible light (λ > 420nm), which is ≈8 times that of Ti-based MOF photocatalysts reported so far. This work provides a new strategy to design Ti-MOF photocatalysts and understand their structure-property relationship.

Donor–Acceptor Type Solvatochromic Flavonoid Materials Fluorphores for Polarity Sensing and Real‐Time Temperature Monitoring

AbstractElectron donor–acceptor (D–A) molecules are emerging tools for designing sensitive luminogens, attracting significant research attention. However, due to poor quantum yields under certain conditions, current D–A fluorophores often suffer from fluorescence quenching in practical applications. Developing new D–A dyes and functional composites is crucial for expanding their applications. Here, a novel donor–acceptor type flavonoid dye molecule, namely “AFL”, exhibiting both polarity‐dependent fluorescence emission wavelength shift and viscosity‐dependent intensity change, for polarity measurement and temperature sensing is designed and synthesized. Because the intramolecular charge transfer (ICT) can be enhanced by a decrease of excited state energy caused in high‐polarity organic solvents, AFL undergoes fluorescence emission wavelength shift that shows fluorescence color response to solvents of different polarities and hence differentiates between them. Moreover, the actual temperature can be monitored by the as‐designed AFL@tetradecanoic acid (AFL@TA) sensor. By combining with TA, viscosity sensitively changes upon the temperature change of insoluble composites, thus realizing the fluorescence intensity response to temperature. Remarkable recyclable performance and satisfactory mechanical properties are integrated. This study provides a promising approach to developing a new D–A fluorescent probe and furnishes perspectives on the potential of such D–A type flavonoid material in stimuli‐responsive systems with a focus on visualization sensing technology.

The Reduced Barrier for the Photogenerated Charge Migration on Covalent Triazine‐Based Frameworks for Boosting Photocatalytic CO2 Reduction Into Syngas

AbstractPhotocatalytic CO2 reduction together with hydrogen generation is a promising approach to generate syngas, the photogenerated electron migration from photosensitizers to the catalytic active sites is the rate‐determining step. Herein, an integrative strategy is presented by covalently grafting metal complexes into donor–acceptor covalent triazine‐based frameworks. The catalytic active sites are integrated with the photosensitizer units by covalent linkages to form an extended π‐conjugated framework, which significantly reduces the energy barrier for the migration of the photogenerated charge carriers, resulting in high activity and durability in photocatalytic CO2 reduction into syngas under visible light irradiation. The CO and H2 evolution amounts in 1.5 h are 1086 and 1042 µmol g−1, respectively, which greatly surpass those in the host‐guest counterparts. Furthermore, selective adsorption for CO2 over N2 renders this photocatalytic system to be effective for syngas production from the simulated flue gas. This study provides new approaches to construct the integrative photocatalytic systems for solar‐to‐chemical energy conversion.

Thermomechanically and Conformationally Consistent Coarse-Graining of Donor–Acceptor Polymers via Energy Renormalization Approach

Thermomechanically and Conformationally Consistent Coarse-Graining of Donor–Acceptor Polymers via Energy Renormalization Approach

Molecular models of PM6 for non-fullerene acceptor organic solar cells: How DAD and ADA structures impact charge separation and charge recombination.

The quadrupole moment of a non-fullerene acceptor (NFA) generated by the constituent electron donor (D) and acceptor (A) units is a significant factor that affects the charge separation (CS) and charge recombination (CR) processes in organic photovoltaics (OPVs). However, its impact on p-type polymer domains remains unclear. In this study, we synthesized p-type molecules, namely acceptor-donor-acceptor (ADA) and donor-acceptor-donor (DAD), which are components of the benchmark PM6 polymer (D: benzodithiophene and A: dioxobenzodithiophene). Planar heterojunction films, a model of bulk heterojunction, were prepared using ADA, DAD, and PM6 as the bottom p-type layers and Y6 NFA as the top n-type layer. Flash-photolysis time-resolved microwave conductivity, femtosecond transient absorption spectroscopy, and quantum mechanical calculations were employed to probe the charge carrier dynamics. Our findings reveal that while the subtle difference in quadrupole moment and energy gradient of the p-type materials has a minimal influence on CS, the molecular type (ADA or DAD) significantly affects the bulk CR. This study expands the understanding of how the p-type component and its conformation at the p/n interface impact the CS and CR in OPVs, highlighting the critical role of molecular donors in optimizing device performance.

Alternating Donor‐Acceptor Ladder‐Type Heteroarene for Efficient Photothermal Conversion via Boosting Non‐Radiative Decay

The development of novel ladder‐type conjugated molecules is crucial for advancing supramolecular chemistry and material science. In this study, we report a straightforward synthesis of new alternating donor‐acceptor (D‐A) ladder‐type heteroarene, FCDTDPP, and demonstrate its application as photothermal agent for imaging and cancer therapy. FCDTDPP is constructed by vinylene bridge between cyclopentadithiophene (D) and diketopyrrolopyrrole (A) through intramolecular Friedel‐Crafts type reaction. FCDTDPP exhibits unique combination of good molecular planarity, efficient intra/inter‐molecular mixed D‐A interactions, and local aromaticity. These features collectively contribute to its broad and intense absorptions with narrow bandgap in red band of the spectra, coupled with multiple vibrational absorption feature, thereby enhancing non‐radiative decay process and resulting in efficient photothermal conversion property. FCDTDPP and its nanoparticles (NPs) exhibit superior photothermal conversion performance and stability under 660 nm laser irradiation. Moreover, in vitro studies reveal that FCDTDPP NPs possess excellent biocompatibility, low cytotoxicity, and robust photothermal therapeutic efficacy, a finding further corroborated by preliminary in vivo experiments in tumor‐bearing mice. This work charts a novel course for the molecular engineering of organic photothermal conversion systems, propelling relevant research forward.

Hydrodynamic Fluidic Pump Empowered Sensitive Recognition and Active Transport of Hydrogen Peroxide in 1D Channels.

Through synthetic chemistry, the development of molecular devices for the precise selective recognition and active transport of small molecules stands as one of the most ambitious objectives in extensive medical, environmental, and biological applications. The periodical channels of the metal-organic frameworks (MOFs) with excellent chemical affinity offer vast regulatory space for reaching this goal. Herein, by post-modifying fluorescent probes and ionic liquid molecules into the Zr-MOFs (NU-1000), a donor-acceptor (D-A) system within the periodical 1D channels is created to construct a hydrodynamic fluidic pump within the abundant 1D channels. Irradiation with light serves to initiate and direct fluid motion, expediting the transport of H2O2 molecules to the active site, thus boosting the sensor sensitivity through gas enrichment. The rapid mass transfer, characterized by a high flow rate and intensified interaction between the D-A system and H2O2 molecules, enables the detection of H2O2 at concentrations as low as 20 ppb. Besides, with the aid of incident light, the pump system exhibits active transport characteristics by transporting radicals derived from H2O2 against a concentration gradient, reaching a remarkable 10th cycle. The strategy of achieving active transport of small molecules through pore modification holds promise for advancing the development of artificial bioactive channels.

Alternating Donor-Acceptor Ladder-Type Heteroarene for Efficient Photothermal Conversion via Boosting Non-Radiative Decay.

The development of novel ladder-type conjugated molecules is crucial for advancing supramolecular chemistry and material science. In this study, we report a straightforward synthesis of new alternating donor-acceptor (D-A) ladder-type heteroarene, FCDTDPP, and demonstrate its application as photothermal agent for imaging and cancer therapy. FCDTDPP is constructed by vinylene bridge between cyclopentadithiophene (D) and diketopyrrolopyrrole (A) through intramolecular Friedel-Crafts type reaction. FCDTDPP exhibits unique combination of good molecular planarity, efficient intra/inter-molecular mixed D-A interactions, and local aromaticity. These features collectively contribute to its broad and intense absorptions with narrow bandgap in red band of the spectra, coupled with multiple vibrational absorption feature, thereby enhancing non-radiative decay process and resulting in efficient photothermal conversion property. FCDTDPP and its nanoparticles (NPs) exhibit superior photothermal conversion performance and stability under 660 nm laser irradiation. Moreover, in vitro studies reveal that FCDTDPP NPs possess excellent biocompatibility, low cytotoxicity, and robust photothermal therapeutic efficacy, a finding further corroborated by preliminary in vivo experiments in tumor-bearing mice. This work charts a novel course for the molecular engineering of organic photothermal conversion systems, propelling relevant research forward.

Quantum chemical tailoring of intrinsic donor–acceptor configurations as efficient nonlinear optical materials

Quantum chemical tailoring of intrinsic donor–acceptor configurations as efficient nonlinear optical materials

Tunable Isometric Donor‐Acceptor Wurster‐Type Covalent Organic Framework Photocathodes

AbstractCovalent organic frameworks (COFs) offer remarkable versatility, combining ordered structures, high porosity, and tailorable functionalities in nanoscale reaction spaces. Herein, we report the synthesis of a series of isostructural, photoactive Wurster‐type COFs achieved by manipulating the chemical and electronic nature of the Wurster aromatic amine building blocks. A series of donor‐acceptor‐donor (D‐A‐D) Wurster building block molecules was synthesized by incorporating heteroaromatic acceptors with varying strengths between triphenylamine donor groups. These tailored building blocks were integrated into a 2D COF scaffold, resulting in highly crystalline structures and similar morphologies across all COFs. Remarkably, this structural uniformity was also achieved in the synthesis of homogeneous and oriented thin films. Steady‐state photoluminescence revealed a tunable red‐shift in film emission exceeding 100 nm, demonstrating effective manipulation of their optical properties. Furthermore, photoelectrochemical (PEC) water splitting studies exhibited a doubled current density (8.1 μA cm−2 at 0.2 VRHE) for the COF with the strongest acceptor unit. These findings highlight the potential of Wurster D‐A‐D COFs in photoelectrochemical water splitting devices and pave the way for further exploration of chemical functionality‐reactivity‐property relationships in this promising class of photoactive materials.

Two-Step Design Rule for Simultaneously High Conductivity and Seebeck Coefficient in Conjugated Polymer-Based Thermoelectrics.

The trade-off between enhancing conductivity (σ) through doping while concurrently observing a reduction in the Seebeck coefficient (S) presents a key challenge in organic thermoelectrics. Here, a two-step structural design strategy is developed, where the first step enhances the backbone planarity which enhances the conductivity by an improved ordering of conjugated polymers (CPs). The second step, which is fluorination of the backbone, improves the Seebeck coefficient by the controlled induction of energetic disorder, stemming from the fluorine's disruption of the homogeneous electrostatic potential across the CP backbone. This strategy is applied to two series of donor-acceptor (D-A) types of CPs based on the BDT donor unit and BDD and TT as acceptor units, respectively. A maximum power factor (PF) over 155 (142.7±12.7)µWm-1K-2, coupled with S ≈202 (194.6±7.6)µVK-1 is achieved, leading to up to 32-fold enhancement of the PF compared to the initial non-planar and non-fluorinated polymer. This study provides valuable conceptual insights for designing CPs with high conductivity and Seebeck coefficient.

Enhanced Coplanarity and Giant Birefringence in Hydroxypyridinium Nitrate via Hydrogen Bonding between Planar Donors and Planar Acceptors

Enhanced Coplanarity and Giant Birefringence in Hydroxypyridinium Nitrate via Hydrogen Bonding between Planar Donors and Planar Acceptors

Enhanced Coplanarity and Giant Birefringence in Hydroxypyridinium Nitrate via Hydrogen Bonding between Planar Donors and Planar Acceptors.

Birefringent crystals, which possess optical anisotropy, are important optical components. However, designing and synthesizing birefringent crystals faces the challenge of achieving anisotropic structures, especially coplanar geometries. Herein, we achieve a significant birefringence in an ionic compound (C5H6ON)+(NO3)-, (4-hydroxypyridinium nitrate, 4HPN) by hydrogen bonding between planar donors and planar acceptors. We demonstrate that the interactions between the planar hydrogen bond donor ((C5H6ON)+) and planar hydrogen bond acceptor ((NO3)-) ensure the coplanarity during the crystal packing, generating the desired giant optical anisotropy. On two manually cut crystal chips, we observe a = 0.494 (= 0.593), which is the largest among nitrates, or hydroxypyridinium derivatives. This value already surpasses those of the benchmark crystals, e.g., YVO4 and CaCO3, commonly used in the UV to visible and near IR spectral range. 4HPN also exhibits a strong second harmonic generation response (9.55 × KDP). This strategy offers a promising avenue for the design and development of birefringent crystals with potential applications in optical communication, sensing and signal processing devices.

Solvent Dictated Organic Transformations.

Solvent plays an important role in many chemical reactions. The C-H activation has been one of the most powerful tools in organic synthesis. These reactions are often assisted by solvents which not only provide a medium for the chemical reactions but also facilitate reaching to the product stage. The solvent helps the reaction profile both chemically and energetically to reach the targeted product. Organic transformations via C-H activation from the solvent assistance perspective has been discussed in this review. Various solvents such as tetrahydrofuran (THF), MeCN, dichloromethane (DCM), dimethoxyethane (DME), 1,2-dichloroethane (1,2-DCE), dimethylformamide (DMF), dimethylsulfoxide (DMSO), isopropyl nitrile (iPrCN), 1,4-dioxane, AcOH, trifluoroacetic acid (TFA), Ac2O, PhCF3, chloroform (CHCl3), H2O, N-methylpyrrolidone (NMP), acetone, methyl tert-butyl ether (MTBE), toluene, p-xylene, alcohols, MeOH, 1,1,1-trifluoroethanol (TFE), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), tert-amyl alcohol and their roles are discussed. The exclusive role of the solvent in various transformations has been deliberated by highlighting the substrate scope, along with the proposed mechanisms. For easy classification, the review has been divided into three parts: (i) solvent-switched divergent C-H activation; (ii) C-H bond activation with solvent as the coupling reagent, and (iii) C-H activation with solvent caging and solvent-assisted electron donor acceptor (EDA) complex formation and autocatalysis.

Self-assembled properties of water cuboids

Although liquid water and ice are characterised by predominantly tetrahedral coordination, small water clusters often exhibit a cubic structural motif. In this article, the stability of hydrogen-bonded water nanostructures in the form of n 1×n 2×n 3 cuboids is investigated. The requirement for complete hydrogen bonding imposes a strong constraint on their structure. The equations of the donor–acceptor balance are derived, from which all possible forms of completely hydrogen-bonded cuboids are deduced. The flexible non-additive AMOEBA potential is used for geometric optimisation of the set of configurations with different directions of hydrogen (H-) bonds. It has been established that the majority of completely hydrogen-bonded structures are formed by one layer of fused cubes. The lowest energy configurations of the, in fact, bilayer structures are formed by trans-configurations of transverse pairs of molecules, although some H-bonds are broken in this case. It is noted that the structure of the cuboids may result from the assembly of short nanotubes and smaller cuboids. On the other hand, unrealised H-bonds at the corners of the cuboids make it possible to assemble larger bilayer structures.

Manipulating Intramolecular Charge Transfer in Terpyridine Derivatives towards "Turn-On" Fluorescence Chemosensors for Zn2.

A series of donor-acceptor (D-A) terpyridine derivatives with various intramolecular charge transfer interactions have been successfully synthesized bearing phenyl, methoxyphenyl, N-butyldiphenylamine (DPA), and triphenylamine (TPA) as electron-donors and terpyridine (TPY), 2,6-di(pyrazin-2-yl)pyridine (PYDPZ), and N,N-dimethylated PYDPZ (PYDPZ-2CH3) as electron acceptors. Upon the introduction of pyrazine rings instead of pyridine ones and further selective N,N'-dimethylation, the intramolecular D-A interactions are significantly enhanced, resulting in the remarkable reduced intramolecular charge transfer (ICT) transitions and quenched PL emissions in CH2Cl2 solution. However, their ICT emissions are clearly recovered upon adding Zn2+. Especially, for double positively charged compound 12, the Zn2+-induced "turn-on" green emission (λmax, em = 518 nm, Φ = 0.24) with excellent sensitivity (I/I0 = 77) and selectivity (IZn/ICd = 23) is detected. Under the optimized experimental condition (EtOH-H2O (9:1, v/v), containing 0.05 M HEPES buffer (pH = 7.4)), this probe is used to quantitative determination of Zn2+ in a water sample with an average recovery of 97.5%. Furthermore, the probe is applied to imaging of Zn2+ ions in HeLa cells and its mechanism is confirmed by the molecular dynamics simulation, in which lower coulomb potential for membrane surface adsorption and energy barrier for membrane translocation can be found.

Origin of the intermolecular forces that produce donor–acceptor stacks in π-conjugated charge-transfer complexes

The attraction between π-conjugated planar electron donor and acceptor molecules that form many stable charge-transfer (CT) complexes has been explained by quantum chemical CT interactions, although the fundamental origin remains unclear. Here, we demonstrate the mechanism of CT complex formation by potential energy map analysis for TTF–CA and BTBT–TCNQ, using energy decomposition of intermolecular interaction by symmetry-adapted perturbation theory (SAPT) combined with coupled cluster calculation. We find that the source of attraction between donor and acceptor molecules is ascribed primarily to the dispersion force and also to the electrostatic force. In contrast, the contribution of CT interactions to the attractive forces is minimal. We demonstrate that the highly directional feature of the exchange repulsion force, coupled with the attractive dispersion and electrostatic forces, is crucial in determining the intermolecular arrangements of actual CT crystals. These findings are key for understanding the unique structural and electronic properties of π-conjugated CT complexes.

Electronic Coupling Between Perovskite Nanocrystal and Fullerene Modulates Hot Carrier Capture

AbstractThe efficient harnessing of hot carriers holds transformative potential for next‐generation optoelectronic devices. Halide perovskites, with their remarkably long carrier lifetimes exceeding 10 picoseconds, stand at the forefront of this research frontier. Yet, a fundamental paradox persists: why does efficient hot carrier capture remain elusive despite these extended lifetimes? Here, this conundrum is unraveled by constructing a donor–acceptor model system: perovskite nanocrystal and fullerene hybrids. It is demonstrated that the challenge lies not only in the carrier lifetime itself but in the nature of the coupling between donor and acceptor components. Remarkably, it is discovered that the formation of ground‐state complexes, with effective coupling across a wide energy range, not only overcomes the initially forbidden hot carrier capture within these hybrids but also dramatically enhances it, achieving a ≈76% hot carrier capture efficiency. This finding shifts the paradigm of hot carrier capture from extending carrier lifetimes to engineering donor–acceptor coupling, illuminating a path toward practical hot carrier applications.