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In this article, we describe a series of complex salts in which electron-rich {FeII(CN)5}3- centers are coordinated to pyridyl ligands with electron-accepting N-methyl/aryl-pyridinium substituents. These compounds have been characterized by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Molecular quadratic nonlinear optical (NLO) responses have been determined by using hyper-Rayleigh scattering (HRS) at 1064 nm, and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d → π* metal-to-ligand charge-transfer (MLCT) bands. The relatively large static first hyperpolarizabilities, β0, increase markedly on moving from aqueous to methanol solutions, accompanied by large red-shifts in the MLCT transitions. Acidification of aqueous solutions allows reversible switching of the linear and NLO properties, as shown via both HRS and Stark experiments. Time-dependent density functional theory and finite field calculations using a polarizable continuum model yield relatively good agreement with the experimental results and confirm the large decrease in β0 on protonation. The Stark-derived β0 values are generally larger for related {RuII(NH3)5}2+ complexes than for their {FeII(CN)5}3- analogues, consistent with the HRS data in water. However, the HRS data in methanol show that the stronger solvatochromism of the FeII complexes causes their NLO responses to surpass those of their RuII counterparts upon changing the solvent medium.

Six new complex salts trans-[Ru II Cl(pdma) 2 L] [PF 6 ] n [pdma = 1,2-phenylenebis(dimethylarsine); L = (E,E,E)-1,6-bis(4-pyridyl)hexa-1,3,5-triene (bph), n = 1, 5; L = N-methyl-4- [(E)-2-(4-pyridyl) -methyl-4-[2-(4-pyridyl)ethynyl]pyridinium (Mebpa + ), n = 2, 11] have been prepared. The electronic absorption spectra of 5 and 7-11 display intense, visible metal-to-ligand charge-transfer (MLCT) bands, with  max values in the range 434-492 nm in acetonitrile. Cyclic voltammetric studies reveal reversible Ru III/II waves with E 1/2 values in the range 1.06-1.15 V vs. Ag-AgCl, together with irreversible L-based reduction processes. Along with a number of previously reported related compounds (B. J. Coe et al., J. Chem. Soc., Dalton Trans., 1996, 3917; 1997, 591; 2000, 797), salts 5 and 7-11 have been investigated by using Stark (electroabsorption) spectroscopy in butyronitrile glasses at 77 K. These studies have afforded dipole moment changes  12 for the MLCT transitions which have been used to calculate molecular static first hyperpolarizabilities  0 according to the two-state equation  0 = 3 12 ( 12 ) 2 /(E max ) 2 ( 12 = transition dipole moment, E max = MLCT energy). MLCT absorption and electrochemical data show that a trans-{Ru II Cl(pdma) 2 } + centre is considerably less electron-rich than a {Ru II (NH 3 ) 5 } 2+ unit. Although the  0 responses of the pdma complexes are only a little smaller than those of their {Ru II (NH 3 ) 5 } 2+ analogues, this result is partly attributable to unexpected changes in the relative  12 values on freezing. Thus, substantial increases in  12 for the arsine compounds act to partially offset the  0 -decreasing influence of their higher E max values when compared with the analogous pentaammine species. Single crystal X-ray structures have been obtained for the salts 1·2.5MeCN, 4·2MeCN, 7 and 11, but only 1·2.5MeCN adopts a non-centrosymmetric space group (Fdd2) such as may show bulk NLO effects.

Polymers with the ability to heal themselves could provide access to materials with extended lifetimes in a wide range of applications such as surface coatings, automotive components and aerospace composites.Here we describe the synthesis and characterisation of two novel, stimuli-responsive, supramolecular polymer blends based on p-electron-rich pyrenyl residues and p-electron-deficient, chain-folding aromatic diimides that interact through complementary p-p stacking interactions. Different degrees of supramolecular "cross-linking" were achieved by use of divalent or trivalent poly(ethylene glycol)-based polymers featuring pyrenyl end-groups, blended with a known diimide-ether copolymer. The mechanical properties of the resulting polymer blends revealed that higher degrees of supramolecular "cross-link density" yield materials with enhanced mechanical properties, such as increased tensile modulus, modulus of toughness, elasticity and yield point. After a number of break/heal cycles, these materials were found to retain the characteristics of the pristine polymer blend, and this new approach thus offers a simple route to mechanically robust yet healable materials.

Electronically complementary, low molecular weight polymers that self-assemble through tunable π-π stacking interactions to form extended supramolecular polymer networks have been developed for inkjet printing applications and successfully deposited using three different printing techniques. Sequential overprinting of the complementary components results in supramolecular network formation through complexation of π-electron rich pyrenyl or perylenyl chain-ends in one component with π-electron deficient naphthalene diimide residues in a chain-folding polyimide. The complementary π-π stacked polymer blends generate strongly colored materials as a result of charge-transfer absorption bands in the visible spectrum, potentially negating the need for pigments or dyes in the ink formulation. Indeed, the final color of the deposited material can be tailored by varying the end-groups of the π-electron rich polymer component. Piezoelectric printing techniques were employed in a proof of concept study to allow characterization of the materials deposited, and a thermal inkjet printer adapted with imaging software enabled in situ analysis of the ink drops as they formed and of their physical properties. Finally, continuous inkjet printing allowed greater volumes of material to be deposited, on a variety of different substrate surfaces, and demonstrated the utility and versatility of this novel type of ink for industrial applications.