Synthesis of Novel Donor–π–Acceptor Chromophores with Dipicolinate as Acceptor

Three novel donor–π–acceptor (D–π–A) chromophores, with dipicolinate as acceptor, have been synthesized. All the compounds were characterized by ¹H NMR, infrared (IR) spectroscopy, mass spectrometry (MS), and elemental analysis.     

Donor–Acceptor Mechanism of Complex Formation

The gas-phase van der Waals complexes formed in the course of donor–acceptor interaction are shown to become coordination compounds only in the crystalline state. With close lengths of the covalent-ionic and coordination bonds, their energies differ by 100 kJ. This energy difference is due to the work spent to overcome van der Waals forces during the formation of complex ions from interacting molecules.     

Oligothiophene-Ring-Strapped Perylene Bisimides: Functionalizable Coaxial Donor–Acceptor Macrocycles

Aesthetic designs from nature enable new knowledge to be gained and, at the same time, inspire scientific models. In this context, multicomponent macrocycles embody the advantage of precisely positioning the structural units to achieve efficient communication between them. However, the construction of a functionalizable macrocycle for ultrafast charge separation and stabilization has not been attempted. Herein, we report the synthesis, crystal structure, and transient absorption of a new functionalizable macrocycle consisting of an oligothiophene-ring-strapped perylene bisimide. Transient absorption results point to a sequential improvement in charge separation and stabilization from the macrocycle to the corresponding linear dimer and 2D polymer due to the unique design. Our macrocycle design with a supportive spatial arrangement of the donor and acceptor units will inspire the development of more complex synthetic systems with exciting electron-transfer and charge-separation features.     

Excited Donor–Acceptor Complexes in the Polymerization of Vinyl Monomers

Butyl methacrylate was found to affect the composition of radical intermediates formed in the photoreduction of benzophenone with triethylamine. In the presence of the monomer, the yield of free radicals decreased and the yield of complexes of the geminate radical pair increased. This was explained by the formation of excited ternary complexes resulted from the interaction of the excited triplet state of benzophenone with the ground-state complex of butyl methacrylate and triethylamine. The substituent effect in benzophenone on the stability of the radical complex was studied. The reaction rate constant for the decay of the radical complex was correlated with the Hammett ⁰ _c constant that determines the mesomeric effect of the substituent.     

Ethenesulfonyl Fluoride: The Most Perfect Michael Acceptor Ever Found?

The kinetics of the reactions of ethenesulfonyl fluoride (ESF) with sulfonium and pyridinium ylides were measured photometrically to determine the electrophilicity parameter of ESF according to the correlation lg k_{20 °C}=s_N(N+E). With E=?12.09, ESF is among the strongest Michael acceptors in our comprehensive electrophilicity scale, which explains its excellent performance in reactions with many nucleophiles. Its predicted usability as a reagent in electrophilic aromatic substitutions with electron‐rich arenes was confirmed by uncatalyzed reactions with alkyl‐substituted pyrroles.     

What Makes a Strong Organic Electron Donor (or Acceptor)?

Organic electron donors are of importance for a number of applications. However, the factors that are essential for a directed design of compounds with desired reduction power are not clear. Here, we analyze these factors in detail. The intrinsic reduction power, which neglects the environment, has to be separated from extrinsic (e.g., solvent) effects. This power could be quantified by the gas‐phase ionization energy. The experimentally obtained redox potentials in solution and the calculated ionization energies in a solvent (modeled with the conductor‐like screening model (COSMO)) include both intrinsic and extrinsic factors. An increase in the conjugated π‐system of organic electron donors leads to an increase in the intrinsic reduction power, but also decreases the solvent stabilization. Hence, intrinsic and extrinsic effects compete against each other; generally the extrinsic effects dominate. We suggest a simple relationship between the redox potential in solution and the gas‐phase ionization energy and the volume of an organic electron donor. We finally arrive at formulas that allow for an estimate of the (gas‐phase) ionization energy of an electron donor or the (gas‐phase) electron affinity of an electron acceptor from the measured redox potentials in solution. The formulas could be used for neutral organic molecules with no or only small static dipole moment and relatively uniform charge distribution after oxidation/reduction.     

Synthesis of OMS Materials and Investigation of Their Acceptor–Donor Characteristics

Three ordered mesoporous siliceous (OMS) materials known as MCM41s—unmodified MCM-41C16 (“C16”), and two MCM41s with different surface functionalities: MCM-41C16-SH (“C16-SH”) and MCM-41C16-NH₂ (“C16-NH₂”)—were synthesized and studied by inverse gas chromatography in order to determine their acceptor–donor properties. The specific retention volumes of nonpolar and polar probes that were chromatographed on these ordered mesoporous silica adsorbents were evaluated under infinite dilution conditions. Two methods were employed to calculate the standard free energy of adsorption, ΔG _ads, of each chromatographed probe on the basis its specific retention volume. These ΔG _ads values were then employed to estimate the van der Waals contribution and the specific contribution of the free surface energy for each MCM41. DN values (donor numbers, based on the Gutmann scale) and AN* values (acceptor numbers, based on the Riddle–Fowkes scale) were employed to determine the values of parameters that characterize the ability of the MCM41s to act as electron acceptors (parameter: K _A) and donors (parameter: K _D). Considering the different compositions of the probes, each of which has different acceptor–donor properties, a new chromatographic test to supplement the Grob test is suggested.     

Relationship between Reactivity Ratios and Configuration for Donor—Acceptor Type Copolymers

For binary copolymers from an acrylic monomer (acceptor type, M¹) and an aromatic-substituted monomer (donor type, M₂) a linear relation between log (r₂/r¹) and the probability of “coisotactic” alternating addition is observed. This can be a proof for the influence of monomer polarity on the copolymer configuration.     

Ring-Opening 1,3-Aminochalcogenation of Donor–Acceptor Cyclopropanes: A Three-Component Approach

A 1,3-aminothiolation was realized by reacting 2-substituted cyclopropane 1,1-dicarboxylates with sulfonamides and N-(arylthio)succinimides. Under Sn(OTf)₂ catalysis the transformation proceeded smoothly to the corresponding ring-opened products bearing the sulfonamide in the 1-position next to the donor and the arylthio residue in the 3-position next to the acceptor. The procedure was extended to the corresponding selenium analogues by employing N-(phenylseleno)succinimides as an electrophilic selenium source.     

π-Extended Donor–Acceptor Porphyrins and Metalloporphyrins for Antimicrobial Photodynamic Inactivation

Free base, zinc and palladium π-extended porphyrins containing fused naphthalenediamide units were employed as photosensitizers in antimicrobial photodynamic therapy (aPDT). Their efficacy, assessed by photophysical and in vitro photobiological studies on Gram-positive bacteria, was found to depend on metal coordination, showing a dramatic enhancement of photosensitizing activity for the palladium complex.     

Photodissociative Modules that Control Dual-Emission Properties in Donor–π–Acceptor Organoborane Fluorophores

Donor–π–acceptor fluorophores that consist of an electron-donating amino group and an electron-accepting triarylborane moiety generally exhibit substantial solvatochromism in their fluorescence while retaining high fluorescence quantum yields even in polar media. Herein, we report a new family of this compound class, which bears ortho-P(=X)R₂-substituted phenyl groups (X=O or S) as a photodissociative module. The P=X moiety that intramolecularly coordinates to the boron atom undergoes dissociation in the excited state, giving rise to dual emission from the corresponding tetra- and tricoordinate boron species. The susceptibility of the systems to photodissociation depends on the coordination ability of the P=O and P=S moieties, whereby the latter facilitates dissociation. The intensity ratios of the dual emission bands are sensitive to environmental parameters, including temperature, solution polarity, and the viscosity of the medium. Moreover, precise tuning of the P(=X)R₂ group and the electron-donating amino moiety led to single-molecule white emission in solution.     

Geometrical Changes and Their Energies in the Formation of Donor–Acceptor Complexes

We have mapped the energy demands of the geometrical changes in donor–acceptor complexes BH₃NH₃ and AlCl₃NH₃ and in the course of their formation from their monomers. We have varied the individual geometrical parameters systematically and performed ab initio quantum chemical calculations for these structures. We investigated the energy requirements to change bond lengths and bond angles in both the monomers and complexes and the angles of torsion in the complexes. The changes of bond lengths require more energy in the monomers than in the complexes. The energies to change the acceptor bond angles in the monomers are markedly higher than in the complexes. The changes in the geometrical parameters during the complexation process are more moderate in donors than in acceptors, in agreement with prior experimental observations. The geometry versus energy variations related to the process of complexation are in agreement with the notion of relative rigidity of the donor parts and the more compliant nature of the acceptor parts as well as with the notion of competing effects in the structures of the complexes.     

Light-harvesting Complex Ⅱ Sensitized Oxide Photoanodes with Organic Acceptor Molecule as Electron Transfer Mediator

Dye sensitized solar cell（DSSC） is a promising thin film solar cell that has been widely investigated after its birth because of its advantages,such as flexibility,low-cost,easyfabrication and so on[1-3].For DSSCs,sensitizers play a core role due to their responsibility for the generation of the photo carriers resulted from light absorption and the transfer of the photo-generated electrons into semiconductor photoanodes[4].Keywords：Light-harvesting complex Ⅱ; Anthraquinone 2-carboxylic acid; ZnO; TiO2 nanostructure; Solar cell     

Synthesis and Photovoltaic Properties of Donor–Acceptor Oligothiophene Derivatives Possessing Mesogenic Properties

For the purpose of developing novel photovoltaic materials and organic photovoltaic devices with good performance characteristics, 5-cyano-2,2′:5′,2″-terthiophene (3T-CN) and 5-cyano-2,2′:5′,2″:5″,2″′-tetrathiophene (4T-CN) were synthesized. The 3T-CN and 4T-CN were donor–acceptor oligothiophene derivatives possessing mesogenic properties. The photovoltaic properties of 3T-CN and 4T-CN were studied. The rigid and flexible photovoltaic devices were fabricated using 3T-CN, 4T-CN, and 3,4,9,10-perylenetertracarboxylic dianhydride (PTCDA). The results showed that the -CN group played an important role in increasing short circuit current density (I _sc) and power conversion efficiency (PCE). Both rigid device glass-ITO/4T-CN/PTCDA/Al and flexible device PET-ITO (indium tin oxides coated with polyethylene terephthalate)/4T-CN/PTCDA/Al had greater I _sc and PCE compared with rigid device glass-ITO/4T/PTCDA/Al. It was possible that the -CN group, with strong electron-withdrawing character, and mesogenic properties of 4T-CN enhanced the efficiency by promoting forward interfacial electron transfer.      

Chromatographic characterisation of ordered mesoporous silicas. Part II: Acceptor–donor properties

The ordered mesoporous siliceous materials: MCM41C16, MCM41C16-SH and MCM41C16-NH₂ (known as MCMs) having different surface functionalities were studied by inverse gas chromatography to characterise their acceptor-donor properties. The DN values denoting the donor number in the Gutmann scale and the AN* values denoting the acceptor number in the Riddle–Fowkes scale have been chosen in the estimation of the electron-acceptor parameter K_A and electron-donor parameter K_D values. The number and kind of the employed adsorbates have an influence on the results obtained. The problem of the number of adsorbates employed has been considered in the light of both results obtained in the present study and the data available in the literature for siliceous adsorbents with randomly ordered structures. Complementary information was obtained by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy.     

Electrically Conductive π-Intercalated Graphitic Metal-Organic Framework Containing Alternate π-Donor/Acceptor Stacks

Two-dimensional graphitic metal–organic frameworks (GMOF) often display impressive electrical conductivity chiefly due to efficient through-bond in-plane charge transport, however, less efficient out-of-plane conduction across the stacked layers creates large disparity between two orthogonal conduction pathways and dampens their bulk conductivity. To address this issue and engineer higher bulk conductivity in 2D GMOFs, we have constructed via an elegant bottom-up method the first π-intercalated GMOF (iGMOF1) featuring built-in alternate π-donor/acceptor (π-D/A) stacks of Cu^II-coordinated electron-rich hexaaminotriphenylene (HATP) ligands and non-coordinatively intercalated π-acidic hexacyano-triphenylene (HCTP) molecules, which facilitated out-of-plane charge transport while the hexagonal Cu₃(HATP)₂ scaffold maintained in-plane conduction. As a result, iGMOF1 attained an order of magnitude higher bulk electrical conductivity and much smaller activation energy than Cu₃(HATP)₂ (σ=25 vs. 2 S m⁻¹, E_a=36 vs. 65 meV), demostrating that simultaneous in-plane (through-bond) and out-of-plane (through πD/A stacks) charge transport can generate higher electrical conductivity in novel iGMOFs.     

Synthesis,Photophysical and Electronic Properties of New Red-to-NIR Emitting Donor–Acceptor Pyrene Derivatives

We synthesized new pyrene derivatives with strong bis(para-methoxyphenyl)amine donors at the 2,7-positions and n-azaacene acceptors at the K-region of pyrene. The compounds possess a strong intramolecular charge transfer, leading to unusual properties such as emission in the red to NIR region (700 nm), which has not been reported before for monomeric pyrenes. Detailed photophysical studies reveal very long intrinsic lifetimes of >100 ns for the new compounds, which is typical for 2,7-substituted pyrenes but not for K-region substituted pyrenes. The incorporation of strong donors and acceptors leads to very low reduction and oxidation potentials, and spectroelectrochemical studies show that the compounds are on the borderline between localized Robin-Day class-II and delocalized Robin-Day class-III species.     

Single & Two-photon Excited Fluorescence of Two New Compounds with 2-Benzothiazolyl as Electron Acceptor

When certain lasers are used as pump source, some organic molecules can simultaneously absorb two photons to reach one of their excited states and subsequently frequency up-converted fluorescence emission may follow1,2. Compared with common single-photon excited fluorescence (SPEF), this two-photon excited fluorescence (TPEF) is characterized by its excitation process of two-photon absorption (TPA) that presents several advantages including high three-dimensional resolution as well as low…     

Acceleration of the Recombination of Photoexcited Donor—Acceptor Complexes with a High-Frequency Vibrational Mode

The recombination dynamics of ion pairs formed by the photoexcitation of donor—acceptor complexes in a polar solvent was investigated using the stochastic approach. The reorganization of high-frequency intramolecular vibrational modes plays an important role in these reactions. It was shown for the perylene—tetracyanoethylene complex in acetonitrile solution that the overwhelming majority of ion pairs recombined at the hot stage, during solvent polarization relaxation.     

Acceptor tuning effect on TPA-based organic efficient sensitizers for optoelectronic applications—quantum chemical investigation

Structural Chemistry - A new series of triphenylamine (TPA)-based organic dyes (A1-A4) are characterized and implemented as photosensitizers for dye-sensitized solar cells (DSSCs). In the...