Electron-rich heteroaromatic conjugated bipyridine based ruthenium sensitizer for efficient dye-sensitized solar cells

A novel heteroleptic ruthenium complex carrying a heteroaromatic-4,4'-pi-conjugated 2,2'-bipyridine [Ru(II)LL'(NCS)(2)] (L = 4,4'-bis[(E)-2-(3,4-ethylenedioxythien-2-yl)vinyl]-2,2'-bipyridine, L' = 4,4'-(dicarboxylic acid)-2,2'-bipyridine) was synthesized and used in dye-sensitized solar cells, yielding photovoltaic efficiencies of 9.1% under standard global AM 1.5 sunlight.     

Ab initio prediction of the emission color in phosphorescent iridium(III) complexes for OLEDs

We performed fully first principles quantum mechanical calculations of the ground and excited state geometries and harmonic vibrational frequencies of two prototype cationic Ir(III) complexes showing high emission quantum efficiencies. Thanks to recent theoretical advances, we have been able for the first time to simulate their vibrationally resolved emission spectra. Our results, in good agreement with the experiment, allow us to calculate the CIE coordinates and therefore the emission color of this important class of emitters for OLEDs and LECs.     

Modulation of the optical response of polyethylene films containing luminescent perylene chromophores

In this work, two perylene derivatives containing different peripheral alkyl chains (i.e., N,N'-bis-(hexyl)perylene-3,4,9,10-tetracarboxyldiimide (ES-PTCDI) and N,N'-bis-(2'-ethylhexyl)perylene-3,4,9,10-tetracarboxyldiimide (EE-PTCDI)) were synthesized and efficiently dispersed at low loadings (from 0.01 to 0.1 wt %) into linear low-density polyethylene (LLDPE) by processing in the melt. Spectroscopic investigations (UV-vis and fluorescence) combined with quantum-mechanical studies demonstrated the ability of both chromophores to generate aggregates among the planar structure of dyes when dissolved in solution or dispersed into LLDPE above a certain concentration. The data acquired for dyes' dispersions into the polymer matrix reveal that the optical properties and responsiveness to mechanical stimuli are strongly dependent on the compactness of perylene aggregates provided by the different molecular structure of dyes. In particular, the strong intermolecular aggregates of ES-PTCDI resulted in being more resistant toward mechanical stress and less orientable by uniaxial drawing along the drawing direction of the film, whereas the less compact and distorted supramolecular architecture of EE-PTCDI chromophores provided composite films with a remarkable optical response to mechanical solicitations.     

Positivity,symmetry and uniqueness for minimizers of second-order Sobolev inequalities

We prove that minimizers for subcritical second-order Sobolev embeddings in the unit ball are unique, positive and radially symmetric. Since the proofs of the corresponding first-order results cannot be extended to the present situation, we apply new and recently developed techniques.     

Biological buffered saline solution as solvent in agar-carbomer hydrogel synthesis

The role of phosphate buffer saline solution (PBS) was investigated here as a solvent in the polycondensation synthesis of an injectable agar-carbomer based hydrogel, a promising new material specifically intended for regenerative medicine applications. The effects of PBS, with respect to standard distilled water (DW), were quantitatively assessed. Experiments were performed both from physico-chemical and biological points of view. Titration showed higher stability due to the presence of the buffer solution; ESEM analysis confirmed its distribution along the polymeric fibers and infrared spectroscopy showed the consequent anionic nature of the polymeric network. This electrostatic nature of the matrix was confirmed by mass equilibrium swelling data performed at different pH values of the swelling medium. A very relevant role of the solvent was observed also with respect to cell housing inside such hydrogels: living cell counts showed a high amount of cells surviving the latency period of encapsulation in hydrogel when PBS was applied while only very few survived in a deionized water based gel. Obtained data allowed a novel understanding of the causeeffect cascades of all observed phenomena which suggest the PBS fundamental role both in fine control of hydrogel preparation and in material tuning according to the specific needs of different target tissues; the latter being a feature of primary importance when applying hydrogels as cell carriers in regenerative medicine applications.     

Structure‐property relationships in densely grafted π‐stacked polymers

Three methyl end‐capped oligo(ethylene glycol) (MOEG) ethers ( 1b‐d ) and a methoxyderivative ( 1a ) of benzofulvene monomer BF3k were synthesized and induced to polymerize spontaneously by solvent removal to obtain soluble π‐stacked polymers bearing densely grafted MOEG side chains (poly‐ 1b – d ) and model polymer poly‐ 1a. The physicochemical features (e.g., solubility, NMR, MALDI‐TOF, and absorption/emission spectra, as well as MWD, conformation plot, and thermal properties) of the synthesized polymers were compared in a structure‐property relationship study. This approach afforded the following evidence. The structure of poly‐ 1a – d is very similar to that of BF3k , suggesting that the polymerization mechanism is not affected by the presence of the electron‐rich methoxy group or bulkier MOEG side chains. However, the latter appear to be capable of affecting the conformational behavior of the polymer backbone. The solubility of poly‐ 1a – d depends on the number of the oligo(ethylene glycol) monomeric units. In particular, poly‐ 1d , featuring a long MOEG side chain (n = 9), shows an amphiphilic character and is soluble in a number of organic solvents, whereas it interacts with water to give isolated macromolecules in equilibrium with nanosized water‐soluble aggregates. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2446–2461, 2010