Hairpin-shaped heterometallic luminescent lanthanide complexes for DNA intercalative recognition.

Luminescent Ln-Pt2 metallohairpin complexes have been developed, and their intercalative recognition with DNA has been demonstrated with linear dichroism spectroscopy. The heterotrimetallic complexes were formed in a one-step reaction, by assembly of an aminopolycarboxylate ligand, a platinum terpyridine unit, and the lanthanide salt. The metallohairpin complexes bear a neutral lanthanide moiety and two positively charged platinum-containing intercalating units. The Nd(III) analogues are luminescent in the near infrared, and this near-IR luminescence is retained upon binding to DNA. The DNA recognition was demonstrated by linear dichroism spectroscopy. The linear dichroism spectra suggested that the complexes bind perpendicular to the DNA helical axis, confirming intercalative recognition accompanied by dramatic stiffening of DNA, which suggests bis-intercalation of the complex.

Photoinduced energy- and electron-transfer processes within dynamic self-assembled donor-acceptor arrays.

The synthesis and the photophysical properties of a series of noncovalently assembled donor-acceptor systems, dyads, is reported. The presented approach uses an "innocent" coordination compound, a scandium(III) acetyl acetonate derivative, as core and promotor of the dyad formation. Intercomponent photoinduced energy transfer or electron transfer within the dynamic assembly, which yields to a statistical library of donor-acceptor systems, is reported. The assemblies for energy-transfer processes are constituted by an energy donor, Ru(bpy)(3)(2+)-based component (bpy = 2,2'-bipyridine), and by an energy-acceptor moiety, anthracene-based unit, both substituted with a chelating ligand, acetyl acetone, that via coordination with a scandium ion will ensure the formation of the dyad. If N,N,N'N'-tetramethyl-2,5-diaminobenzyl-substituted acetyl acetonate ligands are used in the place of 9-acyl-anthracene, intramolecular photoinduced electron transfer from the amino derivative (electron donor) to the Ru(bpy)(3)(2+)-unit was detected upon self-assembly, mediated by the scandium complex. The photophysical processes can be studied on the lifetime of the kinetically labile complexes.

Photoinduced electron transfer between metal-coordinated cyclodextrin assemblies and viologens.

Two novel tris(bipyridine)ruthenium(II) complexes bearing two and six beta-cyclodextrin binding sites on their ligands have been synthesised and characterised. Complex 1, bearing two cyclodextrins, adopts a conformation in aqueous solution where parts of the aromatic ligands are self-included into the cyclodextrin moieties. This results in a loss of symmetry of the complex and gives rise to a much more complicated 1H NMR spectrum than expected. Photophysical studies indicate that the appended cyclodextrins protect the luminescent ruthenium core from quenching by oxygen, which results in longer excited state lifetimes and higher emission quantum yields compared with the reference compound, the unsubstituted ruthenium tris(bipyridine). Inclusion of suitable guests such as dialkyl-viologens leads to a quenching of the luminescence of the central unit. In these supramolecular donor-acceptor dyads an efficient photoinduced electron transfer from the excited ruthenium moiety (the donor) to the viologen unit (the acceptor) is observed. The alkyl chain length of the acceptor plays an important role on the binding properties; when it exceeds a certain limit the binding becomes strong enough for electron transfer to occur. Interestingly, a viologen with only one long alkyl tail instead of two shows no efficient quenching; this indicates that cooperative interactions between two cyclodextrins binding one viologen are essential to raise the binding constant of the supramolecular dyad.