Acceptor Configuration Research Articles

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

2D sp2 carbon-linked benzotrithiophene covalent organic frameworks for selective sulfoxidation with oxygen driven by green light

Covalent organic frameworks (COFs) are promising photocatalysts with excellent chemical stability, broad light absorption, and tailorable molecular structures. To assemble highly crystalline 2D (two-dimensional) COFs, planar molecular units like benzotrithiophene (BTT) and 2,2′-bipyridine (Bpy) are highly desired. Herein, two COFs are assembled by the condensation of benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene-2,5,8-tricarbaldehyde with [2,2′-bipyridine]-5,5′-diacetonitrile and [2,2′-bipyridine]-5,5′-diamine, respectively. An sp2 carbon-linked COF Bpy-sp2c-BTT-COF and an imine-linked COF Bpy-IM-BTT-COF with apparent electron donor–acceptor configuration are readily furnished in which the planarity of Bpy underpins their crystallinity. The sp2-carbon linkage is more essential than the imine linkage in adjusting band structure and facilitating electron transfer over Bpy-sp2c-BTT-COF and Bpy-IM-BTT-COF. Therefore, Bpy-sp2c-BTT-COF demonstrates better performance than Bpy-IM-BTT-COF for selective sulfoxidation with oxygen driven by green light in which superoxide and single oxygen are both involved during the activation of oxygen. The linkage selection for COFs opens new doors into visible light photocatalysts for selective conversions.

Efficient doped and non-doped light-emitting diodes based on a TADF-emitting Cu4Br4 cluster

A sublimable Cu4Br4 cluster, chelated by bidentate N^P ligands with a donor–acceptor configuration, realizes highly efficient doped and non-doped cluster light-emitting diodes.

Peripheral structural modification for devising push–pull strategy into 1,3,5‐triaryl‐2‐pyrazoline‐based compounds for nonlinear optical insights via density functional theory approach

AbstractThe nonlinear optical (NLO) insights of triarylpyrazoline‐based (Z)‐2‐(2‐((7‐(4‐(5‐[2,4‐dimethylphenyl]‐1‐phenyl‐4,5‐dihydro‐1H‐pyrazol‐3‐yl)phenyl)‐4,4,9,9‐tetramethyl‐4,4a,9,10a‐tetrahydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophen‐2‐yl)methylene)‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐yl)malononitrile (PR) and its derivatives P1–P7 were explored in this study. The compounds: PR and P1–P7 having donor–π–acceptor configurations and M06/6‐311G(d,p) functional was selected to inquire the dipole moment (μ), linear polarizability (α), first hyperpolarizability (β), and second hyperpolarizability (γ). The findings of perturbed Kohn–Sham relations were deciphered to derive charge density of the molecules. The optical analysis was performed in gaseous phase and their findings were observed in 544.2–697.1 nm range. Moreover, the natural bond orbitals, frontier molecular orbitals, density of state, and transition density matrices for the aforesaid compounds were also calculated at aforesaid level. Global reactivity parameters of PR and P1–P7 were analyzed by using highest occupied molecular orbital–lowest unoccupied molecular orbital energies. Overall, all above‐mentioned findings revealed significant optical nonlinear response in these pyrazoline‐based scaffold (PR and P1–P7). However, among all the compounds, P3 has shown the highest nonlinearity with maximum μtot, <α>, βtot, and γtot values at 19.4 D, 1.78 × 10−22, 2.57 × 10−27, and 3.13 × 10−32 a.u., respectively. Hence, the current computational study might prove to be fruitful for the exploration of proficient NLO materials for optoelectronic devices.

Mechanistic Approach towards Designing Covalent Organic Frameworks for Photocatalytic Hydrogen Generation

Covalent organic frameworks (COFs) have unique features, including intrinsic porosity, crystallinity, and tunability, making them desirable materials for diverse applications ranging from environmental remediation to energy harvesting. Among these applications, COFs are extensively studied for their photocatalytic hydrogen evolution by converting solar energy into clean and renewable fuel via water splitting. COFs have several advantages over conventional inorganic catalysts, such as tunable band structures, high surface areas, and low cost. However, the research in this field is still in the early stages, and COFs still face some challenges, such as low charge carrier mobility, high exciton binding energy, and poor stability. To overcome these challenges, various design strategies relying on a mechanistic approach have been developed to design and modify COFs for enhanced photocatalytic performance. These include extending the π-conjugation, incorporating heteroatoms or metal complexes, and donor–acceptor (D–A) configuration, which ultimately improves the light absorption charge separation of COFs. Additionally, blending COFs with other functional materials, such as inorganic-organic semiconductors, can create synergistic effects to boost photocatalytic activity. In this review, the design aspects of the fabrication of COFs as effective photocatalysts have been reported.

Isomer and substituent engineering of TADF emitters toward tunable room-temperature phosphorescence

Metal-free organic phosphorescent materials are crucial for the advancement of optoelectronics and bioelectronics. Nonetheless, achieving rational control over the performance of room-temperature phosphorescence (RTP) presents a significant challenge. In this study, two sets of isomeric thermally activated delayed fluorescence (TADF) emitters with a donor–acceptor (D-A) configuration are designed and synthesized. Their RTP efficiency and lifetime are regulated by tuning their energy levels and molecular packing modes through isomer and substituent engineering. All of these materials exhibited afterglow emission, with the exception of 4-CzAIPh. A comprehensive investigation was conducted on the packing modes in the crystalline state, which revealed that the three RTP materials possess strong π-π interactions and numerous intermolecular forces, providing stability to the long-lived triplet excitons of RTP. Especially, 4-CzAIAd demonstrated the fastest intersystem crossing rate, the smallest fractional free volume and relatively larger spin–orbit coupling between its singlet and triplet states, as well as between its triplet state and ground state, which explains its longest phosphorescence lifetime of 301 ms.

Fluorinated Dihydropentalene-1,4-Dione: A Strong Electron-Accepting Unit with Organic Semiconductor Characteristics.

The development of electron-accepting units is of significant importance because the construction of donor (D)-acceptor (A) configurations is an effective strategy for tuning the electronic properties of π-conjugated systems. Although doubly fused pentagons represented by diketopyrrolopyrrole (DPP) have been used as an effective electron-accepting unit, the relatively high-lying frontier molecular orbital levels (FMOs) leave room for further improvement. We report herein the synthesis of a fluorinated dihydropentalene-1,4-dione (FPD) derivative as a strong electron-accepting unit and the development of D-A-D π-extended molecules. X-ray analyses revealed that the presence of fluorine atoms contributed to the formation of high planar structures and slipped-stacked packing. Electrochemical measurements indicated that the FPD derivatives showed relatively lower FMO energy levels than the corresponding DPP-containing derivatives. The D-A-D molecule based on terthiophene and FPD showed semiconducting responses. This study demonstrates that the FPD unit can function as a new acceptor unit for organic semiconductors.

Aggregation-Induced Intermolecular Charge Transfer Emission for Solution-Processable Bipolar Host Material via Adjusting the Length of Alkyl Chain.

Molecules with donor-spacer-acceptor configuration have been developed rapidly given their peculiar properties. How to utilize intermolecular interactions and charge transfers for solution-processed organic light-emitting diodes (OLEDs) greatly relies on molecular design strategy. Herein, soluble luminophores with D-spacer-A motif were constructed via shortening the alkyl chain from nonane to propane, where the alkyl chain was utilized as a spatial linker between the donor and acceptor. The alkyl chain blocks the molecular conjugation and induces the existence of aggregation-induced intermolecular CT emission, as well as the improved solubility and morphology in a solid-state film. In addition, the length of the alkyl chain affects the glass transition temperature, carrier transport and balance properties. The mCP-3C-TRZ with nonane as the spacer shows better thermal stability and bipolar carrier transport ability, so the corresponding solution-processable phosphorescent organic light-emitting diodes exhibit superior external quantum efficiency of 9.8% when using mCP-3C-TRZ as a host material. This work offers a promising strategy to establish a bipolar host via utilizing intermolecular charge transfer process in an aggregated state.

High efficient room temperature phosphorescent materials constructed with methylene molecular configuration.

In this work, we have investigated several pure organic room temperature phosphorescent materials with donor-methylene acceptor configurations with relatively different quantum efficiency. The results show that the introduction of methylene functional group in room temperature phosphorescent materials based on donor-acceptor configuration is more favorable for obtaining higher phosphorescent quantum efficiency in crystal phase environment. More importantly, our calculations reveal the root cause of the excellent quantum efficiency performance after the introduction of methylene groups. The results show that the introduction of methylene can inhibit the structural deformation of molecules during the excited state transition process and give them higher interaction. Moreover, in the donor-acceptor configuration, the heavy atom effect is more favorable to the formation of π-x (X = Br) interaction to accelerate the occurrence of intersystem crossing and achieve a higher intersystem crossing rate. Therefore, the donor-methylene-acceptor molecule is expected to improve the quantum efficiency of room temperature phosphorescence, and the addition of heavy atoms is more conducive to prolong the life of room temperature phosphorescence. This work provides a useful reference for rational design of room temperature phosphorescent materials with high efficiency and long life.

A step-by-step strategy to enhancing the photovoltaic performance of indandione-based polymers

A series of conjugated polymers, poly(2-(5-hexylthiophen-2-yl) methylene-1H-indene-1,3(2H)-dione benzodithiophene) (IND-HT-BDT) and poly(2-(5-hexylthiophen-2-yl) methylene-1H-indene-1,3(2H)-dione fluorinated benzodithiophene) (IND-HT-BDTF), based on 1,3-indandione derivatives are designed and synthesized for organic solar cells (OSCs). The polymers have a typical architecture of donor – acceptor (D-A) configurations with 2-(5-hexylthiophen-2-yl) methylene-1H-indene-1,3(2H)-dione (IND-HT) as the electron acceptor and the benzodithiophene (BDT) or fluorine substituted benzodithiophene (BDTF) as the electron donor. To investigate the photovoltaic properties of the polymers as the polymer donor, inverted OSCs are fabricated based on the polymer as the donor and fullerene acceptor (6,6)-Phenyl C71 butyric acid methyl ester (PC71BM) or 2,2'-((2Z,2'Z)-((12,13-bis(2-butyloctyl)-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno [2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno[3,2-b]indole-2,10-diyl)bis (methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)) dimalononitrile (Y6BO). IND-HT-BDT and IND-HT-BDTF based devices as the polymer donors and Y6BO exhibit the power conversion efficiency (PCE) of 4.82% and 6.43%, respectively, which are better than the corresponding devices based on PC71BM as the acceptor. This is due to the complementary absorption ranges between donor polymers and those Y6BO acceptors.

From para to ortho: Incarnating conventional TADF molecules into AIE-TADF molecules for highly-efficient non-doped OLEDs

Conventional thermally activated delayed fluorescence (TADF) molecules are generally constructed by planar moieties with a linear donor–acceptor (D-A) configuration but suffer from aggregation-caused quenching (ACQ). Herein, we provide a strategy to develop aggregation-induced emission TADF (AIE-TADF) emitters that are consisted of ACQ moieties through the substitute change from para-, meta- to ortho-position, which means incarnating conventional TADF molecules into AIE-TADF molecules. The ortho-substituted molecule exhibits a highly twisted conformation to hinder π-π stacking and thus avoids ACQ, while a large D-A twisted angle contributes to fast reversible intersystem crossing and low non-radiative decay, thus facilitating the AIE-TADF feature in neat film. The ortho-substituted molecule renders the non-doped devices with a high external quantum efficiency of 22.14%. These results certify that adjusting substitute position is a simple and practical strategy for the development of high-efficiency TADF materials and devices.

Thermochromic properties of acridine heterocyclic derivatives with a donor–acceptor configuration

The thermochromic properties of two donor–acceptor type fluorescent molecules DpAn-InAc and DpAn-BzAc in powder- and film-states were studied.

Thiophene-incorporated CTFs with boosted intramolecular charge transfer and defect-abundant networks for potent photosensitized oxidation of organics

Simultaneously modulating the adsorption and electronic properties of pure conjugated polymers for efficient photosensitized oxidation of organics is environmentally desirable but still challenging. Of interest to us in this work was to construct artificial defective donor-sensitizer-acceptor covalent triazine framework (CTF) and probe how the transformation of barely active pure polymers into high-efficiency photosensitizer occurred. The thiophene/cyano (–Th/–CN) donor–acceptor (D–A) configurations in the structural terminations were facilely formed by incorporating thiophene units into CTF (denoted as CTF-xTh), which simultaneously induced plenty of defect sites spread over the polymer networks. Experimental and theoretical studies revealed that the incorporated D–A dyads could serve as charge delivery channels for intramolecular charge transfer transition and render the photogenerated charges spatially delocalized at the –Th/–CN terminated edge sites, which impels the proceeding of photoactivation reaction with oxyanions (represented by HSO5−). Moreover, the edge defects could serve as high-energy adsorption sites for enriching organics (represented by bisphenol-A (BPA)), which enables the generated reactive species to be in close proximity to contaminants to have greater chances of attacking these molecules. With these merits, a 4-fold enhancement of HSO5− conversion and a 10-fold improvement of BPA adsorption were found in Vis/ HSO5−/CTF-5Th system as compared with corresponding pristine CTF system, and thus the overall BPA removal increased by 8 times. This work demonstrated the first instance of using D-A tailored CTF for photosensitized oxidation of organics and provided new opportunities toward designing of novel polymers for visible-light-driven photocatalysis.

Over 17% Efficiency of Ternary Organic Photovoltaics Employing Two Acceptors with an Acceptor-Donor-Acceptor Configuration.

Ternary organic photovoltaics (OPVs) were constructed with one wide-band-gap donor PM6 and two A-D-A-type acceptors (M-series M36 and MQ5) with similar chemical structures. Power conversion efficiency (PCE) of the optimal ternary OPVs reaches 17.24% with 20 wt % MQ5 content, arising from a simultaneously increased short circuit current density (JSC) of 25.36 mA cm-2 and a fill factor (FF) of 76.02% as compared to those of two binary OPVs. The photon harvesting of ternary active layers can be maximized by adjusting the MQ5 content by reason of the complementary absorption spectra of M36 and MQ5. The molecular arrangement of PM6 and M36 can be collectively optimized by introducing an appropriate amount of MQ5 as a morphology regulator for facilitating effective charge transportation in ternary active layers. The improved photon harvesting and charge transport in active layers should be two important factors responsible for JSC and FF improvement of optimal ternary OPVs, respectively. More than an 8.8% improvement of PCE is achieved in ternary OPVs with an appropriate amount of MQ5 as the photon-harvesting enhancer and morphology regulator. The huge potential of A-D-A-type materials in constructing highly efficient OPVs can be further exploited based on a ternary strategy.

Phenanthroimidazole substituted imidazo[1,2-a]pyridine derivatives for deep-blue electroluminescence with CIEy ∼ 0.08

Blue emitting materials with balanced charge carrying capacity are crucial for effective OLED. Phenanthroimidazole based deep blue materials are developed with a donor–acceptor configuration to optimize charge balance in OLEDs. In this work, three new dipolar materials based on the phenanthroimidazole-imidazopyridine conjugated system were synthesized and characterized. The position and number of phenanthroimidazole substituents are changed to study structure property relationships. All derivatives carried superb thermal stability and high photoluminescence quantum yield. Dyesin which phenanthroimidazole chromophore linked at thepara-position of C2 phenyl ring showed the red-shifted emission band. The positive solvatochromism was observed with the increase of solvent polarity, associated with the intramolecular charge transfer at excited state. The electrochemical measurement revealed that the fluorophores have low-lying LUMO energy levels. Further, doped devices were fabricated with these emitters to estimate the EL performances. Among all the emitters, the doped device fabricated with a dye containing phenanthroimidazole chromophore at para-position of C2 phenyl showed superior electroluminescence performance with CIE coordinates (0.16, 0.08).

New Donor–Acceptor–Donor Conjugated Polymer with Twisted Donor–Acceptor Configuration for High-Capacitance Electrochromic Supercapacitor Application

New Donor–Acceptor–Donor Conjugated Polymer with Twisted Donor–Acceptor Configuration for High-Capacitance Electrochromic Supercapacitor Application

Photochemical processes in flavo-enzymes as a probe for active site dynamics: TrmFO of Thermus thermophilus.

Quenching of flavin fluorescence by electron transfer from neighboring aromatic residues is ubiquitous in flavoproteins. Apart from constituting a functional process in specific light-active systems, time-resolved spectral characterization of the process can more generally be employed as a probe for the active site configuration and dynamics. In the C51A variant of the bacterial RNA-transforming flavoenzyme TrmFO from the bacterium Thermus thermophilus, fluorescence is very short-lived (~ 1 ps), and close-by Tyr343 is known to act as the main quencher, as confirmed here by the very similar dynamics observed in protein variants with modified other potential quenchers, Trp283 and Trp214. When Tyr343 is modified to redox-inactive phenylalanine, slower and highly multiphasic kinetics are observed on the picosecond-nanosecond timescale, reflecting heterogeneous electron donor-acceptor configurations. We demonstrate that Trp214, which is located on a potentially functional flexible loop, contributes to electron donor quenching in this variant. Contrasting with observations in other nucleic acid-transforming enzymes, these kinetics are strikingly temperature-independent. This indicates (a) near-barrierless electron transfer reactions and (b) no exchange between different configurations on the timescale up to at least 2 ns, despite the presumed flexibility of Trp214. Results of extensive molecular dynamics simulations are presented to explain this unexpected finding in terms of slowly exchanging protein configurations.

Acceptor-Donor-Acceptor-Type Orange-Red Thermally Activated Delayed Fluorescence Materials Realizing External Quantum Efficiency Over 30% with Low Efficiency Roll-Off.

Two new orange-red thermally activated delayed fluorescence (TADF) materials, PzTDBA and PzDBA, are reported. These materials are designed based on the acceptor-donor-acceptor (A-D-A) configuration, containing rigid boron acceptors and dihydrophenazine donor moieties. These materials exhibit a small ΔEST of 0.05-0.06eV, photoluminescence quantum yield (PLQY) as high as near unity, and short delayed exciton lifetime (τd ) of less than 2.63 µs in 5 wt% doped film. Further, these materials show a high reverse intersystem crossing rate (krisc ) on the order of 106 s-1 . The TADF devices fabricated with 5 wt% PzTDBA and PzDBA as emitting dopants show maximum EQE of 30.3% and 21.8% with extremely low roll-off of 3.6% and 3.2% at 1000 cd m-2 and electroluminescence (EL) maxima at 576 nm and 595nm, respectively. The low roll-off character of these materials is analyzed by using a roll-off model and the exciton annihilation quenching rates are found to be suppressed by the fast krisc and short delayed exciton lifetime. These devices show operating device lifetimes (LT50 ) of 159 and 193 h at 1000 cd m-2 for PzTDBA and PzDBA, respectively. The high efficiency and low roll-off of these materials are attributed to the good electronic properties originatng from the A-D-A molecular configuration.

The Bright Side and Dark Side of Hybrid Organic–Inorganic Perovskites

The previously developed bistable amphoteric native defect (BAND) model is used for a comprehensive explanation of the unique photophysical properties and for understanding the remarkable performance of perovskites as photovoltaic materials. It is shown that the amphoteric defects in donor (acceptor) configuration capture a fraction of photoexcited electrons (holes) dividing them into two groups: higher energy bright and lower energy dark electrons (holes). The spatial separation of the dark electrons and the dark holes and the k-space separation of the bright and the dark charge carriers reduce electron hole recombination rates, emulating the properties of an ideal photovoltaic material with a balanced, spatially separated transport of electrons and holes. The BAND model also offers a straightforward explanation for the exceptional insensitivity of the photovoltaic performance of polycrystalline perovskite films to structural and optical inhomogeneities. The blue-shifted radiative recombination of bright electrons and holes results in a large anti-Stokes effect that provides a quantitative explanation for the spectral dependence of the laser cooling effect measured in perovskite platelets.

Orientation-dependent effects of indeno[1,2-b]indole-spirofluorene donor on photovoltaic performance of D−π−A and D−D−π−A sensitizers

Dyes JY70−73 based on indeno[1,2-b]indole-spirofluorene (IISF) donor have been synthesized and applied in dye-sensitized solar cells, two of them feature donor−π−acceptor (D−π−A) configuration and the others adopt a D−D−π−A structure. Orientation-dependent effects of IISF donor are clearly observed in the photovoltaic properties of D−π−A type dyes JY70 and JY72, though close power conversion efficiency (PCE) achieves finally owing to the trade-off effect of open-circuit voltage (VOC) and short-circuit current density (JSC). By contrast, regioisomeric dyes JY71 and JY73 with an auxiliary diphenylamine donor present a significantly different photovoltaic performance. Under the [Co(phen)3]2+/3+ electrolyte, device based on JY73 gives much higher VOC and JSC, hence a greater PCE (7.40%) which is over two times higher than its regioisomeric JY71 (3.31%). Reasons for that have been systematically investigated. Cocktail co-sensitizations of dyes JY73 and JY70/JY72 both promote the PCEs up to over 8%, and device based on JY72&JY73 achieves the highest PCE of 8.32%.