The six multichromophoric species 1-6, containing the potentially luminescent Ru(II) polypyridine subunits and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene fluorophores (dipyrromethene-BF(2) dyes, herein after called bodipy), have been prepared and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox properties have been investigated (for the structuralformulas of all the compounds, see Figure 1). For comparison purposes, also the same properties of the bodipy-based free ligands have been examined. Three of the multichromophoric species (1-3) are based on the Ru(bpy)(3)-type metal subunit, whereas 4-6 are based on the Ru(terpy)(2)-type metal subunit. Transient absorption spectroscopy at room temperature of all the compounds has also been performed. The absorption spectra of all the metal complexes show features that can be assigned to the Ru(II) polypyridine subunits and to the bodipy centers. In particular, the lowest energy spin-allowed pi-pi* transition of the bodipy groups dominates the visible region, peaking at about 530 nm. All the new complexes exhibit a rich redox behavior, with reversible processes attributed to specific sites, indicating a small perturbation of each redox center and therefore highlighting the supramolecular nature of the multichromophoric assemblies. Despite the good luminescence properties of the separated components, 1-6 do not exhibit any luminescence at room temperature; however, transient absorption spectroscopy evidences that for all of them a long-lived (microsecond time scale) excited state is formed, which is identified as the bodipy-based triplet state. Pump-probe transient absorption spectroscopy suggests that such a triplet state is formed from the promptly prepared bodipy-based (1)pi-pi* state in most cases by the intervention of a charge-separated level. At 77 K, all the complexes except complex 1 exhibit the bodipy-based fluorescence, although with a slightly shortened lifetime compared to the corresponding free ligand(s), and 4-6 also exhibit a phosphorescence assigned to the bodipy subunits. Phosphorescence of bodipy species had never been reported in the literature to the best of our knowledge: in the present cases we propose that it is an effective decay process thanks to the presence of the ruthenium heavy atom and of the closely lying (3)MLCT state of the Ru(terpy)(2)-type subunits.

Over the past five years, the spin-crossover (SCO) phenomenon has experienced a clear new lease of interest from the scientific community coinciding with the recent publication of remarkable new advances. This perspective paper describes five illustrative examples of SCO systems, published during the past twelve months, showing new aspects of the unique and very appealing behaviour of these molecular switches, which may find interesting applications in the near future.

The triplet emitting state of an indacene at 774 nm (of 50 ms life-time) was observed for the first time in new ruthenium(II) complexes based on bipartite ligands carrying one or two indacene subunits linked via phenylethynyl connectors to terpyridine fragments.

A novel type of hybrid material based on a PLGA nanoparticle core and a redox-responsive amorphous organosilica shell have been successfully synthesized. The outer layer is obtained by self-assembly of silicate ions with a silsesquioxane containing a disulfide bridge. These organic linkers work as molecular gates that can be selectively cleaved by reducing agents. This system is particularly suitable for storage and release of hydrophobic molecules, as the treatment with dithiothreitol leaves open doors that allow for the discharge of encapsulated molecules in the organic matrix. Using pyrene as a probe molecule, it has been shown that after partial disruption of the organic–inorganic coating, the release mechanism from PLGA particles fits pretty well into Higuchi’s model, corresponding to a diffusion-mediated process. These nanohybrids impose a better control and slower release of encapsulated molecules than bare PLGA nanoparticles, are reasonably stable in a physiological medium, and show great potential as stimuli-responsive vehicles for drug delivery.

The syntheses, structural features, electrochemical behavior, absorption spectra, and photophysical properties of five mononuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)](2+), RuT(n), and five binuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)Ru(terpy)](4+), RuT(n)Ru, are reported, where n varies from 1 to 5 so that the metal-metal distance is estimated to be 42 A for the largest binuclear complex, RuT(5)Ru (terpy is 2,2':6',2"-terpyridine and DEDBT is 2,5-diethynyl-3,4-dibutylthiophene). The metal-centered oxidation potentials for the mononuclear and binuclear species are slightly more positive than for the reference [Ru(terpy)(2)](2+) complex, owing to the withdrawing nature of the back-to-back terpyridine ligands incorporating the repeat diethynyl-thiophene units. Comparison of the reduction potentials for the mononuclear and binuclear complexes reveals that the reduction steps are localized either at the terpy fragments of the T(n) ligands or at the terpy peripheral ligands. The spectroscopic results (absorption spectra at room temperature, luminescence spectra and lifetimes at room temperature and at 77 K) in acetonitrile solvent are consistent with the establishment of electronic delocalization within the oligomeric diethynyl-thiophene fragments (DEDBT(n)) of the T(n) ligands; however, the results also indicate that the terpy units of these ligands and the DEDBT(n)fragments are not strongly coupled. Both at room temperature and at 77 K, the (3)metal-to-ligand charge-transfer luminescence of RuT(n) and RuT(n)Ru complexes is strongly depressed in the larger species with respect to what happens for n < or = 2 (where the luminescence quantum yield is phi approximately 10(-4)); this is discussed in terms of the possible intervention of triplet levels localized at the oligothiophene DEDBT(n)(fragments.

The coordination chemistry of the polydentate ligand 2,4,6-tris(dipyridin-2-ylamino)-1,3,5-triazine (dpyatriz) with Fe II has been explored, leading through variation of the counterion and the solvent system to the preparation of three different dinuclear complexes: 4 ) 4 (2) and [Fe 2 (dpyatriz) 2 Cl 2 ](CF 3 SO 3 ) 2 (3). The X-ray structure of these compounds has revealed that besides the difference in the noncoordinated anion, complex 1 differs from complex 2 only in the nature of the terminal ligands. Bulk magnetisation studies and Mössbauer spectroscopy have shown that such a subtle difference produces a change to the crystal field on the metal atoms, originating an important disparity of the magnetic behaviour. Thus, complex 1 experiences a partial spin crossover centred at approximately 265 K, whereas com-

No abstract

One of the great challenges underlying the search for molecule-based functional materials is to produce systems exhibiting properties of technological interest that can be tuned and exploited at room temperature. Some landmark achievements in this respect are the discovery of a molecule-based magnet that displays ordering above 300°C, [1] and the preparation of molecular materials that undergo spin-crossover phenomena near room temperature.[2] Spin-crossover materials are based on the ability of certain transition metal ions to interconvert between two labile electronic states with concomitant switching of their color, magnetic properties, and/or molecular structural parameters. [3,4] The transition is triggered by external stimuli, such as electromagnetic radiation, magnetic fields, or pressure/temperature variations. Within crystalline phases, the response to the spin-crossover may be transmitted in a cooperative manner throughout the material, leading to a hysteretic behavior. [5] In such a case, the system becomes bistable and can therefore be considered as an externally addressable molecular switch. Current efforts are aimed at integrating spin-crossover centers into metal organic frameworks (MOFs) to combine the properties derived from the spin transition with other properties, such as chirality, conductivity or those derived from nanoporosity. The molecular approach used in preparing hybrid materials has been mostly exploited to obtain networks that exhibit a wide range of pore sizes and shapes, [6][7][8] with the added potential of offering a variety of other functions, in particular because of the inclusion of transition metals. [9][10][11] This may lead to systems where the multifunctionality is manifested by the coexistence of more than one property, such as ferromagnetism and metal conductivity, [12] with no mutual interdependence. The presence of different functions within a material, however, can occur in such a way that they influence each other in a synergistic manner, thereby producing effects that would not be observed if these properties were not coupled. Remarkable examples are, for instance, the observation of a switchable dielectric constant in a material controlled by the spin state of its spin-crossover centers, [13] or the ability to modify the spin-crossover properties of a nanoporous framework by changing the nature of its guest molecules.[14]We have been engaged for some time in the design and synthesis of sophisticated multidentate N-heterocyclic ligands such as 2,4,6-tris-(di(pyridin-2-yl)amino)-1,3,5-triazine (dpyatriz; Scheme S1), [15] and have studied their ability to combine with paramagnetic ions in the construction of zerodimensional or polymeric metal-organic arrays with interesting magnetic properties. For example, metal-organic open frameworks with unprecedented structures, and which include open-shell metals, have been fully characterized. [16,17] In addition, discrete dinuclear complexes of Fe II with dpyatriz have been obtained, and display (extremely rare) ferromagnetic ...