Assembly of crystalline halogen-bonded materials by physical vapor deposition

Polycrystalline halogen-bonded assemblies fabricated by physical vapor deposition (PVD) exhibit controllable morphologies and microstructures. Although the solid-state packing may vary going from a solution crystal growth process (used for chromophore single-crystal determination) to a vapor-phase deposition process (used for PVD film fabrication), the corresponding film microstructures are independent of the substrate surface chemistry.     

Preparation of zwitterionic electron acceptors and donors

The reactions of 4, 4'-bipyridine and nicotinamide with 1, 3-propane sultone yields zwitterionic electron acceptors. Reaction of dimethylaminoethyl ferrocene with 1, 3-propane sultone yields a zwitterionic ferrocene electron donor. The electron acceptors and donor are reduced and oxidized to the respective radical anions and ferrocenyl cation. Dipropyl-4, 4'-bipyridinium disulfonate and the ferrocene derivative quench the excited Ru(bipy)₃²⁺.     

Charge-transfer intensity in complexes with symmetrically equivalent acceptors

Mulliken's model for the intensity of charge-transfer absorption bands in donor/acceptor complexes is extended to transition-metal compounds. Attention is focused on the analysis of systems containing a central metal ion and symmetrically equivalent π-acceptor ligands. The theory is illustrated for a one-donor/two-acceptor complex in D_2d point symmetry. Results are stated for symmetries of commonly occurring transition-metal compounds that display well-documented metal-to-ligand charge-transfer transitions.     

Over 10% efficiencies achieved for the PSCs with thick active layer based on D-A copolymer donors and various fullerene acceptors

<正>In comparison with inorganic solar cells,polymer solar cells(PSCs)possess the advantages of light weight and potential low-cost production technology such as roll-to-roll printing production.And the power conversion efficiency(PCE)of the PSCs reached ca.10%recently.However,the high PCE is limited to the PSCs with the low bandgap polymer PBDTTTs as donor and PC70BM as acceptor,and the     

同系列电子给体与同系列电受体电荷转移络合作用的研究

用电子吸收光谱法, 研究了五个电子受体系列和三个电子给体系列以及非同系列的给、受体共48个化合物间的弱电荷转移络合作用。发现所研究的同系列给体与同一受体作用; 或同系列受体与同一给体作用; 或同系列给体与同系列受体作用, 一般存在着明显的CT络合与表观不络合的现象。通常情况下, 同系序数大的化合物呈现表观不络合;有时, 同系序数大和小的化合物, 即同系物的两头均呈现表观不络合现象, 对此种现象用给、受体间前线分子轨道能级关系进行了讨论。     

Donor-substituted diphenylacetylene derivatives act as electron donors and acceptors

Despite the predominant electron donor character of p-phenylenediamine, our studies on extended p-phenylenediamine derivatives show that they can not only be chemically oxidized, giving well-known Wurster-type radical cations, but also be chemically reduced, giving radical anions. Making use of EPR/ENDOR spectroscopy and supported by DFT calculations, we were able to reveal the extent of π-electron delocalization in the paramagnetic species and to shed light onto the geometry and bond lengths. While for the radical anions spin was found to be mostly delocalized into the π-system, the radical cations can be described as essentially N-centered. Furthermore, we performed electrochemical characterizations using cyclic voltammetry to gain insight into the thermodynamics of the redox processes. The photophysical properties of the parent extended p-phenylenediamine were investigated by absorption, emission, and excitation spectroscopy. The fluorescence quantum yield and the excited-state lifetime of the neutral precursors in hexane and acetonitrile were determined to establish elementary differences originating from solvent effects.     

Peroxyl radical acceptors released by polymer materials into the gas phase

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 973–974, April, 1991.     

Engineering tuneable light-harvesting systems with oligothiophene donors and mono- or bis-bodipy acceptors

Oligothiophene-Bodipy-based donor-acceptor systems for light harvesting have been synthesized and characterized. Absorption, excitation, and emission spectra indicate a tuneable and efficient resonance energy transfer from quaterthiophene as donor to mono- and bis-Bodipy as acceptors. This shows that engineering tuneable light harvesting systems is possible based on the combination of oligothiophenes with one or two Bodipy(s).     

Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors

We used luminescent CdSe-ZnS core-shell quantum dots (QDs) as energy donors in fluorescent resonance energy transfer (FRET) assays. Engineered maltose binding protein (MBP) appended with an oligohistidine tail and labeled with an acceptor dye (Cy3) was immobilized on the nanocrystals via a noncovalent self-assembly scheme. This configuration allowed accurate control of the donor-acceptor separation distance to a range smaller than 100 A and provided a good model system to explore FRET phenomena in QD-protein-dye conjugates. This QD-MBP conjugate presents two advantages: (1) it permits one to tune the degree of spectral overlap between donor and acceptor and (2) provides a unique configuration where a single donor can interact with several acceptors simultaneously. The FRET signal was measured for these complexes as a function of both degree of spectral overlap and fraction of dye-labeled proteins in the QD conjugate. Data showed that substantial acceptor signals were measured upon conjugate formation, indicating efficient nonradiative exciton transfer between QD donors and dye-labeled protein acceptors. FRET efficiency can be controlled either by tuning the QD photoemission or by adjusting the number of dye-labeled proteins immobilized on the QD center. Results showed a clear dependence of the efficiency on the spectral overlap between the QD donor and dye acceptor. Apparent donor-acceptor distances were determined from efficiency measurements and corresponding F?rster distances, and these results agreed with QD bioconjugate dimensions extracted from structural data and core size variations among QD populations.     

Fluorescence quenching by charge transfer interaction. Exciplexes of fluorene and hetero-analogues with electron donors and acceptors

The fluorescence quenching of fluorene, dibenzofuran and dibenzothiophen by aliphatic amines (electron donors) and aromatic nitriles (electron acceptors) has been studied in different solvents. Emission spectra, solvent effects and the observed relationship between the quenching rate constants and ionization potentials of the donors or reduction potentials of the acceptors support an electron-transfer mechanism with exciplex formation. Carbazole does not enter in this scheme and is probably quenched via a different mechanism.     

A paper-based resonance energy transfer nucleic acid hybridization assay using upconversion nanoparticles as donors and quantum dots as acceptors

Monodisperse aqueous upconverting nanoparticles (UCNPs) were covalently immobilized on aldehyde modified cellulose paper via reduction amination to develop a luminescence resonance energy transfer (LRET)-based nucleic acid hybridization assay. This first account of covalent immobilization of UCNPs on paper for a bioassay reports an optically responsive method that is sensitive, reproducible and robust. The immobilized UCNPs were decorated with oligonucleotide probes to capture HPRT1 housekeeping gene fragments, which in turn brought reporter conjugated quantum dots (QDs) in close proximity to the UCNPs for LRET. This sandwich assay could detect unlabeled oligonucleotide target, and had a limit of detection of 13 fmol and a dynamic range spanning nearly 3 orders of magnitude. The use of QDs, which are excellent LRET acceptors, demonstrated improved sensitivity, limit of detection, dynamic range and selectivity compared to similar assays that have used molecular fluorophores as acceptors. The selectivity of the assay was attributed to the decoration of the QDs with polyethylene glycol to eliminate non-specific adsorption. The kinetics of hybridization were determined to be diffusion limited and full signal development occurred within 3 min.     

Polyoxometalates as chemically and structurally versatile components in self-assembled materials

Polyoxometalates (POMs) are anionic molecular metal oxides with expansive diversity in terms of their composition, structure, nuclearity and charge. Within this vast collection of compounds are dominant structural motifs (POM platforms), that are amenable to significant chemical tuning with minimal perturbation of the inorganic oxide molecular structure. Consequently, this enables the systematic investigation of these compounds as inorganic additives within materials whereby structure and charge can be tuned independently i.e. [PW₁₂O₄₀]³⁻vs. [SiW₁₂O₄₀]⁴⁻ while also investigating the impact of varying the charge balancing cations on self-assembly. The rich surface chemistry of POMs also supports their functionalisation by organic components to yield so-called inorganic–organic hybrids which will be the key focus of this perspective. We will introduce the modifications possible for each POM platform, as well as discussing the range of nanoparticles, microparticles and surfaces that have been developed using both surfactant and polymer building blocks. We will also illustrate important examples of POM-hybrids alongside their potential utility in applications such as imaging, therapeutic delivery and energy storage.

Polyoxometalates are anionic molecular metal oxides with diversity in composition, structure, nuclearity and charge. Their adaptable chemistry leads to potential for self-assembly with other building blocks into a variety of hybrid structures.     

Dispiroketals in synthesis (Part 5): A new opportunity for oligosaccharide synthesis using differentially activated glycosyl donors and acceptors

The reactivity of dispiroketal protected thioglycosides makes them useful new precursors for oligossaccharide synthesis as is illustrated by the preparation of a protected pentasaccharide unit common to the variant surface glycoprotein of Trypanosoma brucei.     

Hydrogen bonding of water, hydrogen sulphide and related acceptors with electron donors

Properties of hydrogen bonds formed by 1:1 interaction of H₂O with oxygen, nitrogen, sulphur and other electron donors have been evaluated by extended Hückel and CNDO methods and the results are discussed in relation to the experimental data. A detailed analysis of the variation of the dissociation energies and charge densities with bond distances is presented for the amine-water system. 1:2 complexes of water with donors are found to contain weaker hydrogen bonds than 1:1 complexes. Results of molecular orbital calculations on the hydrogen bonding of H₂S and CH₃SH with some donors are presented. The theoretical value of hydrogen bond dissociation energy varies linearly with the overlap population, and stretching force constant of the hydrogen bond as well as with the experimental O—H frequency shift.     

Epitaxial composite layers of electron donors and acceptors from very large polycyclic aromatic hydrocarbons

Large polycyclic aromatic hydrocarbons (PAHs) can be considered as nanographenes, whose electron donating or accepting properties are controlled by their size and shape as well as functionalities in their periphery. Epitaxial thin films of them are targets for optoelectronic applications; however, large PAHs are increasingly difficult to process. Here we show that epitaxial layers of very large unsubstituted PAHs (C(42)H(18) and C(132)H(34)), as well as a mixed layer of C(42)H(18) with an electron acceptor, can be obtained by self-assembly from solution. The C(132)H(34) is by far the largest nanographene that up to now has been processed into ordered thin films; due to its size it cannot be sublimed in a vacuum. Scanning tunneling microscopy (STM) studies reveal that the interaction with the substrate induces a strong perturbation of the electronic structure of the pure donor in the first epitaxial monolayer. In a second epitaxial layer with a donor acceptor stoichiometry of 2:1 the molecules are unperturbed.     

Conformational analysis of the electron-transfer kinetics across oligoproline peptides using N,N-dimethyl-1,4-benzenediamine donors and pyrene-1-sulfonyl acceptors

Photoinduced intramolecular charge separation across proline-bridged donor-acceptor complexes of the type Pyr-(Pro)n-DMPD (where Pyr=pyrene-1-sulfonyl and DMPD=N,N-dimethyl-1,4-phenylenediamine) was studied. The steady-state emission spectrum for n=0, 1, 2, 3 showed an increase in emission intensity with the number of proline residues. Time-dependent emission measured by streak camera showed increasing emission signal amplitude with increasing n, along with a decrease in decay rate. In all these studies, Pyr-Pro was used as a control complex for the decay of the excited pyrene acceptor moiety without the donor DMPD. Detailed photon counting experiments carried out in DMF/water, DMF, and toluene showed single-exponential kinetics for n=0, 1 and multiexponential kinetics for n=2, 3. Rate constants observed in DMF are for n=0, k=approximately 5x10(10) s(-1); n=1, k=9.70x10(8) s(-1); n=2, k=35.9x10(8) s(-1) (70%) and 5.58x10(8) s(-1) (30%); and n=3, k=16.6x10(8) s(-1) (55%) and 3.87x10(8) s(-1) (45%). These results show that a significant percentage of the n=2 and n=3 molecules undergo faster electron transfer than for the n=1 case. Conformational analysis for Pyr-(Pro)n-DMPD molecules in water showed that whereas only one conformation is possible for n=1, eight are possible for n=2, and 32 are possible for n=3. Calculation of the free energy and electronic coupling for these conformers in water showed that only a few of these conformations have the appropriate energy and electronic coupling to be observed in the experimental time window from 20 ps to 20 ns. Assignment of the conformers undergoing electron transfer in Pyr-(Pro)n-DMPD for n=2 and 3 was based on the values for the n=1 case, for which the measured rate constant is approximately 10(9) s(-1) and the calculated electronic coupling matrix element Hda is 297 cm(-1). The similarity in ground state energy between the cis and trans conformers for n=2 and 3, their use in aqueous-organic and organic solvents, and the nature of the Pyr and DMPD acceptor and donor groups could be contributing causes for the multiexponential kinetics, which was not observed for the metal ion derivatives of proline peptides studied earlier in aqueous solution.