Abdelkrim El-Ghayoury

Multifunctional transition metal complexes: Information transfer at the molecular level

Abstract Recent investigations from our laboratory have described compelling experimental evidence to the effect that polyacetylenes operate as extremely effective molecular-scale wires for conducting electronic charge between redox-active terminals. The unusually low electronic resistivity of polyacetylenic bridges is derived from their relatively accessible HOMOs and LUMOs, which facilitate electron and hole tunnelling over long distances, and because of the excellent electronic coupling that occurs between adjacent carbon atoms, these being in very close proximity. In order to prevent direct participation of the acetylenic bridge in triplet energy-transfer processes or in light-induced electron-transfer reactions, it is prudent to restrict the conjugation length of the bridge to less than five ethynylene groups. We now consider various synthetic strategies for the engineering of such molecular systems that retain the favorable electronic properties of a polyacetylenic bridge but that include a relay or insulator in the bridging moiety. A convenient way to construct such systems is to use a Pt II bis -acetylide as the spacer that separates terminal metal oligopyridine complexes. In this case, the central Pt II complex becomes an insulator. By careful design of the system, this insulatory behavior can be exploited as a means by which to introduce directionality and selectivity into the system, and we demonstrate such effects by using polycyclic hydrocarbons and metalloporphyrins as the photoactive terminals. Similar effects can be obtained with polycyclic hydrocarbons built into the acetylenic wire and, in such cases, the energetics of the bridge can be tuned over an inordinately wide range by varying the extent of conjugation inherent to the aromatic nucleus. A special case is identified in which the polycycle itself possesses vacant coordination sites since the energy of the bridge can be further tuned by external complexation of adventitious cations. In order to provide for an energy gradient along the molecular axis, we have devised a versatile synthetic strategy for attaching different types of ligand to the terminals. This approach also facilitates both extension of the molecular axis and alteration of the molecular shape. The photophysical and electrochemical properties have been recorded for all the molecular systems reported herein and used as a simple experimental means by which to quantify the extent of electronic communication along the molecular axis. For mixed-metal or mixed-ligand systems, rates of intramolecular energy or electron transfer have been measured. In most cases, these rates are extremely fast and testify to the remarkable electronic coupling properties of this family of compounds. Finally, some consideration is given to the preparation of third-generation systems.

Fine‐Tuning the Electronic Properties of Binuclear Bis(terpyridyl)ruthenium(II) Complexes

Vastly improved photophysical properties of terminal RuII terpyridine-based chromophores is achieved by insertion of an ethynylene group between the terpyridine ligand and a covalently linked aromatic nucleus. In the case where the aromatic nucleus possesses vacant coordination sites, as shown in 1, complexation of certain cations (e. g., Zn2+ , Cd2+ , or Ba2+ ) at the central unit gives a further improvement in the photoproperties due to a better blending of the respective LUMO levels.

Cation‐Induced Macroscopic Ordering of Non‐Mesomorphic Modules—A New Application for Metallohelicates

The subtle balance between organized and chaotic domains in the nondiscoidal ligand in the helicate 1, which displays liquid crystalline properties, represents the key element which enables the local molecular architecture to be integrated into an organized macroscopic ensemble.

Grating inscription in picosecond regime in thin films of functionalized DNA

Polymers containing azo-benzene groups are useful holographic recording materials. In these materials the efficient mixed amplitude and phase gratings, frequently accompanied with photoinduced-surface relief gratings, can be inscribed with polarized laser light. The light-induced trans-cis-trans photoisomerization of azo-benzene groups is responsible for optical anisotropy in such systems. The aim of the present work is to study the dynamics of grating inscription in Disperse Red 1 doped deoxyrbonucleic acid- hexadecyltrimethylammonium material (DR1-DNACTMA) using 16 ps laser pulses (532 nm, 1.3 mJ). Results are compared with that obtained for other polymeric matrices loaded with DR1. The dynamics of the grating growth, due to repeated pulses from picosecond laser with 10 Hz repetition rate, was probed by measuring the intensity of the first order of diffraction of a cw He-Ne. We report results in function of the light polarization of writing beams. In this paper we present the first results of the grating inscription in functionalized DNA (in the picosecond pulse regime).

New supramolecular polymers containing both terpyridine metal complexes and quadruple hydrogen bonding unitsElectronic supplementary information (ESI) available: experimental details. See http://www.rsc.org/suppdata/cc/b3/b314459n/

Molecules containing quadruple hydrogen-bonding units as well as metal-complexing terpyridine moieties have been designed and assembled to result in a supramolecular polymer where both interactions are present in the main chain.

π‐Stacked ortho‐Palladated Bipyridine Complexes Exhibiting Unusual Liquid Crystalline Behavior

A columnar structure with lamellar morphology in the liquid crystalline state is displayed by the palladium complex salt 1, which is synthesized from nonmesogenic ligands.

A Neutral Zwitterionic Molecular Solid

We report on the acid ethylenedithiotetrathiafulvaleneamidoglycine (EDT-TTF-CO-NH-CH(2)-CO(2)H; 1; EDT-TTF=ethylenedithiotetrathiafulvalene) and the 1:1 adduct [(EDT-TTF)(·+)-CO-NH-CH(2)-(CO(2))(-)][(EDT-TTF)-CO-NH-CH(2)-(CO(2)H)]·CH(3)OH (2), a new type of hydrogen-bonded, 1:1 acid/zwitterion hybrid embrace of redox peptidics into a two-dimensional architecture, an example of a system deliberately fashioned so that oxidation of π-conjugated cores toward the radical-cation form would interfere with the activity of the appended ionizable residues in the presence of a templating base during crystal growth. First-principles calculations demonstrate that, notwithstanding preconceived ideas, a metallic state is more stable than the hole-localized alternatives for a neat 1:1 neutral acid/zwitterion hybrid. The inhomogeneous Coulomb field associated with proton-shared, interstacks O-H···O hydrogen bonds between the ionizable residues distributed on both sides of the two-dimensional π-conjugated framework leads, however, to a weak hole localization responsible for the activated but high conductivity of 1 S cm(-1). This situation is reminiscent of the role of the environment on electron transfer in tetraheme cytochrome c, in which the protonation state of a heme propionate becomes paramount, or ion-gated transport phenomena in biology. These observations open rather intriguing opportunities for the construction of electronic systems at the interface of chemistry and biology.

Balancing framework densification with charged, halogen-bonded-π-conjugated linkages: [PPh4]2{[E-TTF–I2][Re6Se8(CN)6]}versus[PPh4]2[EDT-TTF–I]2{[EDT-TTF–I][Re6Se8(CN)6]}

The ionic character of a set of two redox linkages and strong, directional halogen bonding at the organic-inorganic interface compromise to produce two materials sharing a common two-dimensional net, eventually extended in a third dimension, although two of the six symmetrical halogen bond acceptors ultimately remain uninvolved as a result of charge densification.

First assembly of copper(I) naphthyridine-based helicates

Copper(I) binds to 2,7-diimino-1,8-naphthyridine in solution to form a mixture of equilibrating mono- and polynuclear complexes, as identified by electrospray MS and monitored by UV-visible spectrophotometric titrations, including a binuclear metallo-helicate for which X-ray data are available but whose formation does not require cooperative associations.

CONSTRUCTION OF NOVEL DITOPIC LIGANDS BEARING FUSED POLYAROMATIC AND ALKYNE SPACERS

Abstract We report the preparation of multi-component molecules based on ethynyl-substituted 2,2′-bipyridine and 2,2′:6′,6″-terpyridine derivatives and para substituted phenyl, naphtalene and anthracene moieties. The triple bonds play the role of a wire while the polyaromatic systems behave as an energy relay subunit.