Strong Electron Donor Research Articles

Tuning the Surface Electron Accumulation Layer of In2 O3 by Adsorption of Molecular Electron Donors and Acceptors.

In2 O3 , an n-type semiconducting transparent transition metal oxide, possesses a surface electron accumulation layer (SEAL) resulting from downward surface band bending due to the presence of ubiquitous oxygen vacancies. Upon annealing In2 O3 in ultrahigh vacuum or in the presence of oxygen, the SEAL can be enhanced or depleted, as governed by the resulting density of oxygen vacancies at the surface. In this work, an alternative route to tune the SEAL by adsorption of strong molecular electron donors (specifically here ruthenium pentamethylcyclopentadienyl mesitylene dimer, [RuCp*mes]2 ) and acceptors (here 2,2'-(1,3,4,5,7,8-hexafluoro-2,6-naphthalene-diylidene)bis-propanedinitrile, F6 TCNNQ) is demonstrated. Starting from an electron-depleted In2 O3 surface after annealing in oxygen, the deposition of [RuCp*mes]2 restores the accumulation layer as a result of electron transfer from the donor molecules to In2 O3 , as evidenced by the observation of (partially) filled conduction sub-bands near the Fermi level via angle-resolved photoemission spectroscopy, indicating the formation of a 2D electron gas due to the SEAL. In contrast, when F6 TCNNQ is deposited on a surface annealed without oxygen, the electron accumulation layer vanishes and an upward band bending is generated at the In2 O3 surface due to electron depletion by the acceptor molecules. Hence, further opportunities to expand the application of In2 O3 in electronic devices are revealed.

Selective sorption of oxygen and nitrous oxide by an electron donor-incorporated flexible coordination network

Incorporating strong electron donor functionality into flexible coordination networks is intriguing for sorption applications due to a built-in mechanism for electron-withdrawing guests. Here we report a 2D flexible porous coordination network, [Ni2(4,4′-bipyridine)(VTTF)2]n(1) (where H2VTTF = 2,2′-[1,2-bis(4-benzoic acid)-1,2ethanediylidene]bis-1,3-benzodithiole), which exhibits large structural deformation from the as-synthesized or open phase (1α) into the closed phase (1β) after guest removal, as demonstrated by X-ray and electron diffraction. Interestingly, upon exposure to electron-withdrawing species, 1β reversibly undergoes guest accommodation transitions; 1α⊃O2 (90 K) and 1α⊃N2O (185 K). Moreover, the 1β phase showed exclusive O2 sorption over other gases (N2, Ar, and CO) at 120 K. The phase transformations between the 1α and 1β phases under these gases were carefully investigated by in-situ X-ray diffraction, in-situ spectroscopic studies, and DFT calculations, validating that the unusual sorption was attributed to the combination of flexible frameworks and VTTF (electron-donor) that induces strong interactions with electron-withdrawing species.

Constructing lipid droplet-targeting photosensitizers based on coumarins with NIR emission

The development of photosensitizers (PSs) with subcellular targeting capability has raised interest for photodynamic therapy (PDT) research. In this work, two coumarin-based photosensitizers (C-S-2 and C-S-3) were designed and synthesized via expanding their π-conjugation, introducing strong electron-donor and acceptor groups, and adopting sulfur substitution strategy. These sulfured-coumarins exhibited near-infrared emission (greater than 650 nm), lipid droplet-targeting ability and obvious photocytotoxicity under laser irradiation. In particular, C-S-3 exhibited better photostability, superior lipid droplet-targeting capability, and stronger photodynamic effect on cancer cells than C-S-2.

A new benzothiazolium-based organic nonlinear optical material DABT

Second-order nonlinear optical (NLO) crystal materials are applied widely. In this work, a new benzothiazolium-based ionic organic NLO material (E)-2-(4-(dimethylamino)styryl)-3-methylbenzo[d]thiazol-3-ium 4-methylbenzenesulfonate (DABT) containing strong electron donor and acceptor was designed and theoretically investigated. A simple approach that can be employed in rapidly and efficiently evaluating the second-order nonlinear properties of organic crystals based on its crystal structure information was also proposed. Results indicate that the as-designed DABT crystal possesses non-centrosymmetric structure with space group P21, and particularly, it exhibits a large static first-order hyperpolarizability of ∼117 × 10−30 esu. Moreover, the optical properties of the DABT, including its permittivity, absorption coefficient, and reflectance, were systematically investigated, revealing that the DABT crystal is an anisotropic and a new and promising material with hydrophobicity and anisotropy, holding great potential applications in nonlinear optics.

An Effective Approach toward Yellow‐to‐Orange Multi‐Resonance TADF Emitters by Integrating Strong Electron Donor into B/N‐Based Polycyclic Architecture: High Performance OLEDs with Nearly 40% EQE

AbstractB/N‐based multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters and the corresponding narrow band emissive organic light‐emitting diodes (OLEDs) exhibit great potential for next‐generation high‐resolution displays. Nonetheless, designing MR‐TADF emitters with emission wavelength over 550 nm remains challenging. Herein, an effective approach toward yellow‐to‐orange MR‐TADF emitters by integrating a strong electron‐donating indolophenazine building block into the B/N‐doped polycyclic aromatic hydrocarbons is proposed. The investigation of photophysical properties reveals that the electron‐donating difference between the donor segments of MR framework has a dramatic influence on the luminescent features, including the emission wavelength and full‐width at half‐maximum (FWHM). These TADF emitters display excellent photophysical characteristics such as near‐unity photoluminescence quantum yields and almost 100% horizontal dipole ratio. As a result, yellow and orange OLEDs employing these emitters achieve state‐of‐the‐art device performances with an ultrahigh external quantum efficiency of up to nearly 40%, power efficiency of 163 lm W−1, and luminance close to 120 000 cd m−2, which set a record among MR‐TADF based OLEDs with emission peaks over 550 nm. More impressively, the fabricated device presents outstanding operational stability of LT99 over 110 h at the initial brightness of 3000 cd m−2.

O,S-Acetals in a New Modification of oxo-Friedel–Crafts–Bradsher Cyclization—Synthesis of Fluorescent (Hetero)acenes and Mechanistic Considerations

This paper presents the use of O,S-acetals in a new modification of the oxo-Friedel-Crafts-Bradsher cyclization. In this reaction, under mild reaction conditions (25 °C), three- and four-ring fused RO-acenes (major) and/or HO(CH2)2S-acenes (minor) are formed, the latter products having never been observed before in this type of cyclization. In this way, two electronically different fluorophores could be obtained in a single cyclization reaction, one of them having strong electron donor properties (+M effect of alkoxy groups) and the other having donor-acceptor properties (+M and -I effects of the HO(CH2)2S-group, Hammett's constants). Further increasing the reaction temperature, HCl concentration or prolonging reaction time, surprisingly, yielded a 2:1 mixture of cis and trans dimeric isomers, as the only products of this cyclization. The DFT calculations confirmed a greater stability of the cis isomer compared to the trans isomer. The formation of unexpected dimeric products and HO(CH2)2S-acenes sheds light on the mechanism of oxo-Friedel-Crafts-Bradsher cyclization, involving competitive O/S atom protonation in strained O,S-acetals and in strain-free side groups of intermediate species.

Novel Carbazole-Based Porous Organic Polymer for Efficient Iodine Capture and Rhodamine B Adsorption.

A new porous organic polymer (CTF-CAR), which takes carbazole as the electron-rich center unit and thiophenes as the auxiliary group, has been synthesized through catalyst-free Schiff-base polymerization. At the same time, the structure, thermal stability, morphology, and other basic properties of the polymer were analyzed by IR, NMR, TGA, and SEM. Then, CTF-CAR was applied to iodine capture and rhodamine B adsorption. Due to its strong electron donor ability and abundant heteroatom binding sites, which have a positive effect on the interaction between the polymer network and adsorbates, CTF-CAR exhibits high uptake capacities for iodine vapor and rhodamine B as 2.86 g g-1 and 199.7 mg g-1, respectively. The recyclability test also confirmed that it has good reusability. We found that this low-cost and catalyst-free synthetic porous organic polymer has great potential for the treatment of polluted water and iodine capture.

Photocatalytic Regeneration of a Nicotinamide Adenine Nucleotide Mimic with Water-Soluble Iridium(III) Complexes.

Nicotinamide adenine nucleotide (NADH) is involved in many biologically relevant redox reactions, and the photochemical regeneration of its oxidized form (NAD+) under physiological conditions is of interest for combined photo- and biocatalysis. Here, we demonstrate that tri-anionic, water-soluble variants of typically very lipophilic iridium(III) complexes can photo-catalyze the reduction of an NAD+ mimic in a comparatively efficient manner. In combination with a well-known rhodium co-catalyst to facilitate regioselective reactions, these iridium(III) photo-reductants outcompete the commonly used [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) photosensitizer in water by up to 1 order of magnitude in turnover frequency. This improved reactivity is attributable to the strong excited-state electron donor properties and the good chemical robustness of the tri-anionic iridium(III) sensitizers, combined with their favorable Coulombic interaction with the di-cationic rhodium co-catalyst. Our findings seem relevant in the greater context of photobiocatalysis, for which access to strong, efficient, and robust photoreductants with good water solubility can be essential.

3 a,6 a-Diaza-1,4-Diphosphapentalenes: Synthesis and Complexation with the Organic π-Acceptor 1,2,4,5-Tetracyanobenzene.

The reaction of PCl3 with diethyl ketazine and 4-phenylcyclohexanone azine results in the formation of 1,4-dichloro-3a,6a-diaza-1,4-diphosphapentalenes which were reduced by magnesium in THF to give corresponding diazadiphosphapentalenes EtMeDDP and PhcHexDDP, containing two-coordinate phosphorus atoms. According to the CVA data, the new diazadiphosphapentalenes are strong electron donors showing oxidation peak potentials at 0.34 and 0.10 V, respectively, (vs. Ag/AgCl). Interaction of 1,2,4,5-tetracyanobenzene (TCNB) with the obtained diazadiphosphapentalenes in any stoichiometry produces sandwich complexes of the composition DDP-TCNB-DDP. Black-purple crystals of π-complexes contain infinite molecular chains with short P⋅⋅⋅P contacts between DDP molecules and short (Csp2 -H⋅⋅⋅N) contacts between TCNB molecules. Calculations showed that each TCNB molecule is an acceptor of ∼0.3e from two DDP molecules. Estimation of the HOMO-LUMO gap from the onset of optical absorption give values of 1.25 eV and 1.31 eV for [(EtMeDDP)2 (TCNB)] and [(PhcHexDDP)2 (TCNB)] respectively.

A theoretical study on the influence of N-containing heterocyclic ligands on the luminescence mechanisms (phosphorescence or TADF) of Au (III) complexes

Au (III) complexes display remarkable emission properties in OLEDs materials due to the high-performance emitters in recent years. Explaining microscopic mechanisms of the luminescence process clearly remain a challenge. The intersystem crossing between the singlet excited state and the triplet excited state in the metal complexes systems plays a central role in determining the fate of excitons and various luminescence pathways. For the planar tridentate coordination complexes of Au (III), it remains unclear what are the key factors that affect the luminescent pathways and thus the quantum efficiency. This work uncovers the relationship between the intersystem crossing processes (include ISC and RISC) and electronic structures of chelated ligands in the Au ( III ) complexes, which is supported by the quantum-chemical calculations. It is found that the modification of strong electron-donating groups (such as –NMe 2 , -NPh 2 ) may reduce the vibration coupling effect and energy gap (Δ E ST ), then open the thermal equilibrium channel, and finally obtain higher quantum yield TADF emitter through the fluorescence process. But the complex that has carbazole group in the auxiliary ligand still can't undergo the RISC process. These may be caused by the various electron delocalization and transition type result from different auxiliary ligands mediated by the N 2 atom. Moreover, the vibration analyses for the phosphorescence emision show that the vibration modes, which make significantly contribute to the reorganization energy, mainly come from the CˆNˆC ligand. While for TADF emission, that is from the auxiliary ligand. This work presents a deep insight into the luminescent mechanism and the key factors affected by the regulation of the ligands in the Au (III) complexes, and provides valuable theoretical basis and reference for the synthesis and design of TADF materials. • The higher SOC effect does not necessarily lead to the TADF process. • The modification of strong electron-donating may reduce the vibration coupling effect and energy gap Δ E ST , finally obtain higher quantum yield TADF emitter through the fluorescence process. • Adding the carbazole group in the auxiliary ligand can enhance the contribution of the CˆNˆC ligand on the reorganization energy.

Thiophene and diaminobenzo- (1,2,5-thiadiazol)- based DAD-type near-infrared fluorescent probe for nitric oxide: A theoretical research.

A near-infrared fluorescent probe (LS-NO) for the real-time detection of nitric oxide (NO) in inflammatory bowel disease (IBD) was developed recently. The probe used oligoglycol morpholine-functionalized thiophene as strong electron donors and diaminobenzene (1,2,5-thiadiazole) as a weak electron acceptor and NO trapping group. It could detect exogenous and endogenous NO in the lysosomes of living cells with high sensitivity and specificity. To further understand the fluorescent mechanism and character of the probes LS-NO and LS-TZ (after the reaction of the probe LS-NO with NO), the electron transfer in the excitation and emitting process within the model molecules DAD-NO and DAD-TZ was analyzed in detail under the density functional theory. The calculation results indicated the transformation from diaminobenzene (1,2,5-thiadiazole) as a weak electron acceptor to triazolo-benzo-(1,2,5-thiadiazole) as a strong electron acceptor made LS-NO an effective "off-on" near-infrared NO fluorescent probe.

Noncovalent interactions engineering construct the fast-kinetics organic cathode for room/low-temperature aqueous zinc-ion battery

Electroactive organic electrode materials are receiving increasing attention in aqueous zinc-ion batteries (AZIBs). However, the insufficient electrical conductivity, sluggish kinetics and intrinsic soluble trait of organic molecules still hinder their application as the electrode material. Here, a carbonyl compound, dibenzo[b,i]thian threne-5,7,12,14-tetraone (DTT) is tightly wrapping by reduced graphene oxide (r-GO) with noncovalent interactions to obtain DTT@r-GO organic cathode material. Benefiting from the π-π coupling, the composite electrode delivers higher surface area, enhanced electron/ion transportation and stable structure, which exhibits superior rate performance (259.1 mAh g−1 at 0.1 A g-1 and 117.7 mAh g−1 at 10 A g−1) and considerable calendar life (4000 cycles with 100 % capacity retention at 10 A g−1). Electrochemical testing and ex-situ analysis prove CO can act as a strong electron donor together with co-accommodation of Zn2+/H+, theoretical calculation confirms the favorable two-step Zn storage configuration during the charge storage process. Furthermore, these AZIBs can steadily power electronic devices at −50 °C, as well as retain a high reversible capacity of 199.5 mAh g−1 at 50 mA g−1 and 100 % capacity retention after 3700 cycles at −20 °C. The work is believed to broaden the insight into noncovalent interactions and inspire the organic electrochemical materials.

In silico screening of ethyl 4-[(E)-(2-hydroxy-4-methoxyphenyl)methyleneamino]benzoate and some of its derivatives for their NLO activities using DFT.

The nonlinear optical (NLO) properties of ethyl 4-[(E)-(2-hydroxy-4-methoxyphenyl)methyleneamino]benzoate (EMAB) and some of its derivatives are investigated herein using the density functional theory (DFT) and time-dependent (TD)-DFT methods. The density functionals B3LYP, CAM-B3LYP, M06-2X and ωB97XD, and basis sets 6-31 + G**, 6-311 + + G** and Def2-TZVPP have been used. From the results, EMAB and its substituted derivatives studied are promising candidates for NLO materials. In all cases, the static first and second hyperpolarizabilities (31.7-86.5 × 10-30 and 84.4-273 × 10-36 electrostatic units (esu), respectively) and the frequency-dependent NLO properties are found to be significantly larger (about 43-103 and 28-76 times greater) than those of the NLO prototypical molecule, para-nitroaniline. Furthermore, the maximum absorption wavelengths of the molecules fall within the UV region of the electromagnetic spectrum. Relative to EMAB, the derivatives have shown improved transparency-nonlinearity trade-offs. Natural bond orbital (NBO) and density of states (DOS) analyses herein revealed effective charge transfer within the molecules studied, especially those with stronger electron donors than that in EMAB (methoxy group). Among the molecules studied, the derivative obtained by substituting EMAB's methoxy group with the pyrrolyl group was found to exhibit the best NLO properties. Conclusively, the NLO activities of EMAB can be significantly improved through the substitution of its methoxy group with stronger electron donors.

A cross-conjugation approach for high-performance diaryl-hemithioindigo photoswitches.

Diaryl-hemithioindigos (diaryl-HTIs) are derivatives of a novel class of highly functionalized indigoid chromophores. In this work a systematic study of the electronic effects on their photoswitching reveals the design principles for achieving an excellent property profile. Two key elements need to be invoked for perfect diaryl-HTI performance, first introduction of strong electron donors and second establishment of cross-conjugation. The resulting photoswitches combine high thermal stability, large extinction coefficients, red-light responsiveness, pronounced photochromism, and strong isomer accumulation in the photostationary states with precise geometry changes. By using the inherent basicity of their strong electron donor moiety, diaryl-HTIs can be rendered into very potent tools for molecular logic applications. We demonstrate a variety of binary logic setups as well as sophisticated three- and four-input keypad locks for sequential logic operations. Three distinct states and up to four different stimuli are invoked for this multi-level molecular information processing. Diaryl-HTIs have thus entered the stage as very capable and promising photoswitch motives for anyone interested in reversible visible- and red-light as well as multi-stimuli responsive molecular behavior.

Modification of Cu–ZnO–ZrO2 catalysts with La2O3 to quantitatively tune Cu+–Cu0 dual sites for hydrogenation of dimethyl adipate to produce 1,6-hexanediol

The strong electron donor–acceptor interaction between lanthanum and copper species retards the aggregation of the copper species, and inhibits the transformation of Cu2O to metallic Cu, thus maintaining a constant ratio of Cu+/(Cu0 + Cu+).

Understanding the reactivity and selectivity of Diels-Alder reactions involving furans.

The reactivity and endo/exo selectivity of the Diels-Alder cycloaddition reactions involving furan and substituted furans as dienes have been computationally explored. In comparison to cyclopentadiene, it is found that furan is comparatively less reactive and also less endo-selective in the reaction with maleic anhydride as the dienophile. Despite that, both the reactivity and the selectivity can be successfully modified by the presence of substituents at either 2- or 3-positions of the heterocycle. In this sense, it is found that the presence of strong electron-donor groups significantly increases the reactivity of the system while the opposite is found in the presence of electron-withdrawing groups. The observed trends in both the reactivity and selectivity are analyzed quantitatively in detail by means of the activation strain model of reactivity in combination with the energy decomposition analysis methods.

Enhanced electrochemical CO2 reduction performance of cobalt phthalocyanine with precise regulation of electronic states.

Herein, we report a facile strategy for constructing hybrid coordination configurations by combining functionalized graphene quantum dots (GQDs) with CoPc (CoPc/R-GQDs, with R being -NH2 or -OH) for electrochemical CO2 reduction. Benefiting from the high density of functional groups that can be provided by GQDs and the strong electron-donating property of -NH2, the examined CoPc/NH2-GQDs achieved a 100% faradaic efficiency for CO formation (FECO) at -0.8 to -0.9 V vs. RHE, and high FECO (over 90%) over a wide potential range of 500 mV. This work has presented a novel approach for catalyst design, specifically involving molecular engineering of quantum dots, which can also be applied to other essential electrochemical reactions.

ESIPT-active cinnamoyl pyrones are bright solid-state emitters: Revisited theoretical approach and experimental study

Excited-state intramolecular proton transfer (ESIPT) is a photophysical process that may lead to superior emission properties. For a long time, cinnamoyl pyrone (CP) derivatives have been classified as non-ESIPT molecules. With the exception of those bearing a strong electron-donor substituent, they have been considered to have no interest from a spectroscopic point of view, because they are virtually not fluorescent in solution. Revisiting their photophysical behaviour in solution shows the complexity of the mechanisms involved. It appeared that CPs with no or weak electron-donor substituents indeed undergo ESIPT, but the facile access to a conical intersection subsequently induces non-radiative deactivation, hence the extinction of fluorescence in solution. When substituted by an electron-donating diethylamino group, the molecules deactivate through a radiative intramolecular charge transfer (ICT) state following an ESIPT process. In the solid state, the restricted access to conical intersection (RACI) makes most of the CP derivatives strongly fluorescent. Whatever the electron-donating strength of their substituent, most of these molecules become good emitters in the solid state, with emission ranging from turquoise blue to deep red. Although they need extensive purification, their one-step synthesis and spectacular aggregation-induced emission (AIE) properties make these molecules good candidates for applications in the field of AIE-probes and photoluminescent materials.

Steric and Electronic Analyses of Ligand Effects on the Stability of σ-Methane Coordination Complexes: A DFT Study

Developing efficient catalysts for methane functionalization is a longstanding goal in inorganic chemistry. Here, we present theoretical calculations to support efforts to synthesize σ-methane complexes that can be studied by NMR spectroscopy. The systems studied are osmium complexes of stoichiometry (C5R5)Os(diphosphine)(CH3)(H)+: when both cyclopentadienyl and diphosphine are relatively strong electron donors, the methyl/hydride structure is in rapid equilibrium with its σ-methane tautomer at low temperatures, as shown experimentally some years ago. Here, using density functional theory, we examine how changing the steric and electronic properties of the ancillary cyclopentadienyl and diphosphine ligands affects the relative energies of the two tautomers, with the goal of identifying a ligand set for which the σ-methane structure, rather than the methyl/hydride form, is the predominant species in equilibrium. We also examine how varying the ancillary ligands affects the barrier for methane dissociation. The calculations suggest that osmium complexes bearing weakly donating and sterically undemanding ligands stabilize the σ-methane structure both relative to its methyl/hydride tautomer and toward dissociation of the methane ligand. More specifically, osmium σ-methane complexes of fluorinated diphosphines (CF3)2PCH2P(CF3)2 and (CF3)2PCF2P(CF3)2 are predicted to be stable enough to be observed by variable-temperature NMR spectroscopy.

A Novel Electron Donor‐Acceptor Carbazole‐Zn(II)Phthalocyanine – Perfluorinated Subphthalocyanine Conjugate: Synthesis, Characterization, and Photoinduced Electron‐Transfer

AbstractPorphyrinoids are considered perfect candidates for the preparation of model electron donor‐acceptor (D‐A) systems as they enable fast and efficient photoinduced electron transfer. Herein, we report on the synthesis and photophysical characterization of a ZnPc−SubPc conjugate covalently connected through a short‐range alkyne spacer. We designed and prepared the conjugate, which comprise, on the one hand, a perfluorinated SubPc with strong electron acceptor character and, on the other, a Pc peripherally functionalized with carbazoles with strong electron donor character. Photoinduced electron transfer events are in‐depth analyzed by several techniques, including steady‐state absorption, time‐resolved emission and transient absorption measurements on different time scales. Our studies confirm a full charge separation occurring from a photoexcited charge transfer state.