Donor-substituted 1,1,4,4-tetracyanobutadienes (TCBDS): new chromophores with efficient intramolecular charge-transfer interactions by atom-economic synthesis.

A wide variety of monomeric and oligomeric, donor-substituted 1,1,4,4-tetracyanobutadienes (TCBDs) have been synthesized by [2+2] cycloaddition between tetracyanoethylene (TNCE) and donor-substituted alkynes, followed by electrocyclic ring opening of the initially formed cyclobutenes. Reaction yields are often nearly quantitative but can be affected by the electron-donating power and steric demands of the alkyne substituents. The intramolecular charge-transfer (CT) interactions between the donor and TCBD acceptor moieties were comprehensively investigated by X-ray crystallography, electrochemistry, UV-visible spectroscopy, and theoretical calculations.

Ground-state equilibrium thermodynamics and switching kinetics of bistable [2]rotaxanes switched in solution, polymer gels, and molecular electronic devices.

We report on the kinetics and ground-state thermodynamics associated with electrochemically driven molecular mechanical switching of three bistable [2]rotaxanes in acetonitrile solution, polymer electrolyte gels, and molecular-switch tunnel junctions (MSTJs). For all rotaxanes a pi-electron-deficient cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF4+ and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers.

Highly efficient third-order optical nonlinearities in donor-substituted cyanoethynylethene molecules.

We investigated the third-order nonlinear optical properties of several donor-substituted cyanoethynylethene molecules in the zero-frequency limit. We observed nonlinearities that are extraordinarily large relative to the small molecular mass of these molecules and that are within a factor of 50 from the fundamental limit. At a wavelength of 1.

Donor-substituted cyanoethynylethenes: pi-conjugation and band-gap tuning in strong charge-transfer chromophores.

An extensive series of silyl-protected cyanoethynylethenes (CEEs) and N,N-dimethylanilino donor-substituted CEEs have been synthesized. More extended chromophores were constructed by selective silyl deprotection and subsequent oxidative acetylenic coupling. The strong electron-accepting nature of the CEEs was revealed by a combination of 13C NMR spectroscopic and electrochemistry measurements.

Limitations on the use of UV/Vis spectroscopy for the evaluation of conjugation effectiveness.

A detailed study on N,N-dimethylanilino donor-substituted cyanoethynylethenes shows that there is no correlation between the effectiveness of the donor-acceptor conjugation pathway and the lowest-energy transition in the UV/Vis absorption spectrum.

Donor-substituted cyanoethynylethenes: powerful chromophores for opto-electronic applications.

Donor-substituted cyanoethynylethenes (CEEs) were synthesised, structurally characterised and investigated for their electronic and two-photon absorption properties, revealing exceptionally strong intramolecular charge-transfer interactions.

Novel extended tetrathiafulvalenes based on acetylenic spacers: synthesis and electronic properties.

A selection of mono- and diacetylenic dithiafulvalenes was synthesized and employed for the construction of extended tetrathiafulvalenes (TTFs) with hexa-2,4-diyne-1,6-diylidene or deca-2,4,6,8-tetrayne-1,10-diylidene spacers between the two 1,3-dithiole rings. By stepwise acetylenic scaffolding using (E)-1,2-diethynylethene (DEE) building blocks, an extended TTF containing a total of 18 C(sp) and C(sp(2)) atoms in the spacer was prepared. The versatility of the acetylenic dithiafulvene modules was also established by the efficient synthesis of a thiophene-spaced TTF, employing a palladium-catalyzed cross-coupling reaction.

Coordination and oxidative addition at a low-coordinate rhodium(I) beta-diiminate centre.

The reaction of 14e [L(Me)Rh(coe)] (1; L(Me)[double bond]ArNC(Me)CHC(Me)NAr, Ar[double bond]2,6-Me(2)C(6)H(3); coe[double bond]cis-cyclooctene) with phenyl halides and thiophenes was studied to assess the competition between sigma coordination, arene pi coordination and oxidative addition of a C-X bond. Whereas oxidative addition of the C-Cl and C-Br bonds of chlorobenzene and bromobenzene to L(Me)Rh results in the dinuclear species [[L(Me)Rh(Ph)(micro-X)](2)] (X=Cl, Br), fluorobenzene yields the dinuclear inverse sandwich complex [[L(Me)Rh](2)(anti-micro-eta(4):eta(4)-PhF)]. Thiophene undergoes oxidative addition of the C-S bond to give a dinuclear product.