Gallium(I)-alkaline earth metal donor-acceptor bonds

Compounds with a gallium-alkaline earth metal bond, [(eta(5)-C(5)Me(5))(2)Ca-Ga(eta(5)-C(5)Me(5))], [(eta(5)-C(5)Me(5))(2)(THF)Sr-Ga(eta(5)-C(5)Me(5))], and [(eta(5)-C(5)Me(5))(2)Ba-{Ga(eta(5)-C(5)Me(5))}(2)], were prepared.     

From group 13-group 13 donor-acceptor bonds to triple-decker cations

Donor-acceptor bonding between group 13 elements seems counter-intuitive because one normally thinks of e.g. boron and aluminium compounds as classical Lewis acids. Indeed, many such compounds have achieved industrial prominence in this regard. Recently, however, it has become possible to stabilize these and other group 13 elements in the +1 oxidation state as opposed to the archetypical +3 oxidation state. Moreover, it turns out that in the +1 oxidation state these species are excellent donors--hence the formation of these unprecedented donor-acceptor bonds. The discovery of such bonds has led, albeit indirectly, to the development of triple-decker main group cations. This aspect is also covered in the review.     

The strength and length of donor-acceptor bonds in molecular complexes

Numerous published data on the structure and thermodynamics of formation of molecular complexes are analyzed. The enthalpies of complexation (−ΔH) are related to the characteristic parameter Δr = [r _DA−a ₁(r _D+r _A)], where r _DA is the donor-acceptor bond length determined by microwave spectroscopy and X-ray analysis, r _D and r _A are the tabulated values of the homopolar covalent radii of the heteroatoms that form the donor-acceptor bond, and a ₁ is an empirical coefficient equal to 0.901±0.007. The relation between −ΔH and Δr values has the form −ΔH = a ₂/Δr (a ₂ = 21.6±1.6 kJ Å mol⁻¹), with a mean relative error of approximation of about 15% and a correlation coefficient of 0.97. As the strength of the complex increases, the donor-acceptor bond length approaches the sum of the heteropolar covalent radii of the atoms involved in the bond (Δr tends to zero). At Δr ≫ 1, the strength of complexes is determined by weak van der Waals interactions between the complex components and the −ΔH values tend to zero. Dedicated to the memory of E. N. Guryanova (1911–2004), a prominent scientist who formulated the basic principles elaborated by her disciples in this review. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1869–1878, October, 2007.     

CNT-CdTe versatile donor-acceptor nanohybrids

Single wall carbon nanotubes (SWNT) and multiwall carbon nanotubes (MWNT) were linked to thioglycolic acid (TGA)-capped CdTe nanoparticles (NP) through electrostatic interactions producing photoactive superstructures. The novel nanohybrids were characterized both in the ground and excited states with specific accent on electron-transfer chemistry. In fact, both assays provide kinetic and spectroscopic evidence that support a partial transfer of charge density, with rapid formation of microsecond-lived radical ion pair states. Since nanotubes provide a quick transportation route of charge carriers to the electrode, we took this remarkable finding further and constructed photoelectrochemical cells. Photocurrents were generated through the implementation of CdTe and SWNT or MWNT, which serve as excited-state electron donor components and electron acceptors, respectively.     

Rapid thermally assisted donor-acceptor catenation

Charged donor-acceptor [2]catenanes containing cyclobis(paraquat-p-phenylene) as the ring component can be synthesised in yields of up to 88% in under one hour by heating two precursors in the presence of macrocyclic polyether templates in N,N-dimethylformamide at 80 °C.     

酞菁一富勒烯给受体体系研究进展

酞菁的大π共轭体系使其具有良好的电子给予能力和对可见光的强烈吸收性质,可作为人工光合作用体系中的光捕捉单元．富勒烯具有独特的三维笼状结构,几乎所有反应中都具有低的重组能,是良好的电子或能量受体．将富勒烯与酞菁结合起来,集两个光活性实体于一身,由于酞菁和富勒烯给受体之间的电子相互作用,又赋予其新的性质,具有良好的应用前景,是富勒烯和酞菁领域中的研究热点．本文将酞菁．富勒烯给受体体系分为共价和非共价两种连接方式,介绍其结构与性质以及两者的相互关系,总结了其在有机太阳能电池、非线性光学和液晶性等方面的应用进展,展望了该体系的未来发展趋势．     

Some amine-interhalogen electron donor-acceptor systems

Several new interhalogen-amine addition compounds have been prepared: 4-Picoline·IBr; Isoquinoline·IBr; Acridine·IBr; Isoquinoline·ICl; Acridine·ICl; Isoquinoline·ICl₃; Acridine·ICl₃. In addition to 1:1 type compounds, thermal studies have shown the existence of: Pyridine·2IBr; IBr·2Acridine; ICl·2Acridine; ICl₃·2Acridine. A compound, Acridine·2IBr apparently exists, but loses one mole IBr at 110° to form the 1:1 compound. Trends among the melting points of the 1:1 addition compounds are interpreted as indicating a decrease in electron acceptor strength of the interhalogens in the order ICI₃ > ICI > IBr. Addition compounds of non-1:1 stoichiometry are also briefly discussed.     

Helical chirality in donor-acceptor catenanes

A [2]catenane in which the macrocyclic polyether, bisparaphenylene[34]crown-10, is interlocked with the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), is shown by dynamic (1)H NMR spectroscopy, using (i). neutral and (ii). anionic chiral shift reagents (CSRs), to exist at low temperatures (197 K) in acetone-d(6) solutions as 1:1 and 2:1 mixtures of diastereoisomeric complexes and salts, respectively, as a consequence of the helical chirality associated with the [2]catenane interacting with the CSRs.     

Dynamic chirality in donor-acceptor pretzelanes

[Figure: see text]. A series of donor-acceptor pretzelanes has been synthesized, using self-assembly and template-directed protocols, and the dynamic processes that these pretzelanes undergo have been investigated in solution. These compounds exist as libraries of diastereoisomers as a result of their multiple stereoelements, which are dynamically interconverted by several different, in some cases competing, processes. Altering the structure of the pretzelanes changes the rates and mechanisms by which these diastereoisomers equilibrate. Additionally, inserting an element of fixed chirality allows the equilibrium to be biased, while maintaining the barrier to the equilibration processes. These results bode well for the future construction of molecular devices based on switchable diastereoisomerism involving metastable states.     

Hydrogen bonds, improper hydrogen bonds and dihydrogen bonds

The structures, interaction energies and vibrational spectra of a large number of molecular complexes, formed by binary combination of the covalent hydrides of some of the elements of the first two rows of the periodic table, have been determined by means of ab initio molecular orbital theory at the MP2 level, using the 6-311++G(d,p) basis set. The results are discussed in terms of a variety of different types of interaction experienced by the monomer species as they undergo association, namely conventional hydrogen bonding, improper hydrogen bonding, dihydrogen bonding and electron donor–acceptor interaction.     

Conjugated oligomers with terminal donor-acceptor substitution

Conjugated oligomers represent a prominent class of compounds from a viewpoint of their theory, synthesis, and applications in materials science. Push-pull substitution with an electron donor D at one end of the conjugation and an electron acceptor A at the other end results in them having outstanding optical and electronical properties. This Review highlights fundamental synthetic strategies for the preparation of such oligomers with n repeat units (n=1, 2, 3, 4, ..) and the rules that govern their linear and nonlinear optical properties (absorption, frequency doubling and tripling). The unification of chemical, physical, and theoretical aspects with an interdisciplinary image of this class of compounds is attempted herein.     

Thiophene donor-acceptor [2]rotaxanes

A series of the thiophene donor-acceptor [2]rotaxanes have been synthesized based on the inclusion complexes of cyclobis(paraquat- p-phenylene) (CBPQT4+) with thiophene, bithiophene, and terthiophene. The maximum wavelength of the charge-transfer band strongly depends on the number of thiophene units, while the association constant does not. These donor-acceptor pairs will be fascinating constituents for optoelectronic and electromechanical materials.     

Blue-colored donor-acceptor [2]rotaxane

[reaction: see text] A guest molecule-a bis-N-tetraethyleneglycol-substituted 3,3'-difluorobenzidine derivative-has been synthesized, and its complexation with the host, cyclobis(paraquat-p-phenylene), has been investigated. This host-guest complex was then employed in the template-directed synthesis of a blue-colored [2]rotaxane. The color of this [2]rotaxane arises from the charge-transfer absorption band between the HOMO of the guest and the LUMO of the host. This host-guest complex, and the derived [2]rotaxane, completes the donor-acceptor-based RGB (red/green/blue) color complex set.     

Hybrid molecular nanostructures with donor-acceptor chains

We have fabricated hybrid molecular chain structures formed by electron acceptor compound 1 and electron donor molecules 2 and 3 at the liquid/solid interface of graphite surface.The structural details of the mono-component and the binary assemblies are revealed by high resolution scanning tunneling microscopy (STM).Compound 1 can form two well-ordered lamellar patterns at different concentrations.In the co-adsorption structures,compounds 2 and 3 can insert into the space between molecular chains of compound 1 and form large area well-ordered nanoscale phase separated lamellar structures.The unit cell parameters for the coassemblies can be "flexibly" adjusted to make the electron donors and acceptors perfectly match along the molecular chains.Scanning tunneling spectroscopy (STS) results indicate that the electronic properties of individual molecular donors and acceptors are preserved in the binary self-assembly.These results provide molecular insight into the nanoscale phase separation of organic electron acceptors and donors on surfaces and are helpful for the fabrication of surface supramolecular structures and molecular devices.     

Charge recombination in excited donor-acceptor complexes

The influence of the excitation pulse carrier frequency on the dynamics of ultrafast charge recombination in donor-acceptor complexes was studied in the limit of strong electron coupling. An increase in the carrier frequency of excitation pulses invariably decreased the effective rate constant. The dependence of the degree to which the decay of the excited state deviated from the exponential law on reaction exothermicity and the dynamic characteristics of the medium was revealed.