Pablo Gaviña

Kinetic competition in liquid electrolyte and solid-state cyanine dye sensitized solar cells

The photovoltaic performance of liquid electrolyte and solid-state dye sensitized solar cells, employing a squarilium methoxy cyanide dye, are evaluated in terms of interfacial electron transfer kinetics. Dye adsorption to the metal oxide film resulted in a mixed population of aggregated and monomeric sensitizer dyes. Emission quenching data, coupled with transient absorption studies, indicate that efficient electron injection was only achieved by the monomeric dyes, with the aggregated dye population having an injection yield an order of magnitude lower. In liquid electrolyte devices, transient absorption studies indicate that photocurrent generation is further limited by slow kinetics of the regeneration of monomeric dye cations by the iodide/iodine redox couple. The regeneration dynamics are observed to be too slow (≫ 100 µs) to compete effectively with the recombination of injected electrons with dye cations. In contrast, for solid-state devices employing the organic hole conductor spiro-OMeTAD, the regeneration dynamics are fast enough (≪ 1 µs) to compete effectively with this recombination reaction, resulting in enhanced photocurrent generation.

Electrochemical and Spectroscopic Properties of Cyclometallated and Non-Cyclometallated Ruthenium(II) Complexes Containing Sterically Hindering Ligands of the Phenanthroline and Terpyridine Families

Two series of cyclometallated and noncyclometallated ruthenium(II) complexes incorporating mono- or disubstituted 1,10-phenanthroline- and 2,2′:6′,2′′-terpyridine-type ligands have been synthesized and characterized. An X-ray crystal structure for one of the complexes, Ru(ttpy)(mapH)-(Cl)(PF6), has been obtained (mapH = 2-p-anisyl-1,10-phenanthroline; ttpy = 4′-tolyl-2,2′:6′,2′′-terpyridine). Distinct electrochemical and photophysical properties have been observed for the two series: a remarkable feature is the observation of relatively long-lived MLCT excited states (from 70 to 106 ns at room temperature in CH3CN) for three of the cyclometallated complexes. A discussion is given on the role of factors like sigma donation by the cyclometallating ligands, interligand steric hindrance and interligand π-π interactions that affect the electrochemical and spectroscopic properties.

Selective and sensitive chromogenic detection of cyanide and HCN in solution and in gas phase

Two triphenylmethane based chemodosimeters for selective and chromogenic sensing of cyanide anions in aqueous environments and of hydrogen cyanide in gas phase were prepared and studied.

Deep-red-emitting electrochemical cells based on heteroleptic bis-chelated ruthenium(II) complexes.

Two ruthenium(II)-based complexes were prepared that show intense deep-red light emission at room temperature. Solid-state electroluminescent devices were prepared using one of the ruthenium complexes as the only active component. These devices emit deep-red light at low voltages and exhibit extraordinary stabilities, demonstrating their potential for low-cost deep-red light sources.

Electrochemically induced molecular motions in a copper(I) complex pseudorotaxane

A pseudortaxane consisting of a coordinating ring, a molecular thread bearing two different coordination sites and a copper(I) ion displays electrochemically induced motions of the ring from one side to the other.

Self-Assembly of a Copper(II)-Based Metallosupramolecular Hexagon

The self-assembly of a 1:1 mixture of copper(II) ions and a rigid heteroditopic ligand L containing phen and terpy binding units gives rise in the solid state to green crystals of a hexanuclear metallamacrocycle 1. X-ray crystallography reveals that 1 consists of molecular hexagons of the grid-type family in which each metal ion is bound to two different ligands through the phen and terpy units, plus a weakly coordinated PF6 (-) anion in a highly distorted octahedral geometry. ES-MS studies of acetonitrile solutions of L and copper(II) in a 1:1 ratio show mixtures of polynuclear complexes in which trinuclear L3Cu3 species are predominant.

Effect of metal complexation on the conductance of single-molecular wires measured at room temperature.

The present work aims to give insight into the effect that metal coordination has on the room-temperature conductance of molecular wires. For that purpose, we have designed a family of rigid, highly conductive ligands functionalized with different terminations (acetylthiols, pyridines, and ethynyl groups), in which the conformational changes induced by metal coordination are negligible. The single-molecule conductance features of this series of molecular wires and their corresponding Cu(I) complexes have been measured in break-junction setups at room temperature. Experimental and theoretical data show that no matter the anchoring group, in all cases metal coordination leads to a shift toward lower energies of the ligand energy levels and a reduction of the HOMO-LUMO gap. However, electron-transport measurements carried out at room temperature revealed a variable metal coordination effect depending on the anchoring group: upon metal coordination, the molecular conductance of thiol and ethynyl derivatives decreased, whereas that of pyridine derivatives increased. These differences reside on the molecular levels implied in the conduction. According to quantum-mechanical calculations based on density functional theory methods, the ligand frontier orbital lying closer to the Fermi energy of the leads differs depending on the anchoring group. Thereby, the effect of metal coordination on molecular conductance observed for each anchoring could be explained in terms of the different energy alignments of the molecular orbitals within the gold Fermi level.

Boolean operations mediated by an ion-pair receptor of a multi-readout molecular logic gate

A heteroditopic BODIPY dye that performs all basic Boolean operations with a cation (K(+)) and an anion (F(-)) as inputs and absorption, transmission and fluorescence as outputs is described. The molecular logic gate can also act as a digital comparator between the inputs.

BODIPY dyes functionalized with 2-(2-dimethylaminophenyl)ethanol moieties as selective OFF–ON fluorescent chemodosimeters for the nerve agent mimics DCNP and DFP

Two OFF–ON fluorescent chemodosimeters based on a BODIPY core for the detection of nerve agent mimics have been synthesized. Their reactivity towards diethylcyanophosphonate (DCNP) and diisopropylfluorophosphate (DFP) has been tested in organic and aqueous phase. These chemodosimeters selectively detect the nerve agent mimics with good LODs. The chemodosimeters hold their sensing properties on solid supports, allowing the preparation of a hand held sensing kit. The sensing in solid–liquid phase has been demonstrated. The X-ray structure of compound 2 has been resolved.

A rotaxane with two Ru(terpy)2 derivatives as stoppers

Starting from organic fragments, a [2]-rotaxane is constructed using pure coordination chemistry; threading of a string into a ring is directed by CuI complexation and the blocking reaction involves coordination of RuII to terminal chelates.