RESUMEN
A series of new amphiphilic phosphonium materials that combine the electronic features of phospholes with self-assembly features of lipids were synthesized. Variable concentration/temperature and 2D NMR studies suggested that the systems undergo intramolecular conformation changes between a "closed" and "open" form that are triggered by intermolecular interactions. The amphiphilic features of the phospholium species also induce liquid crystalline and soft crystal phase behavior in the solid state, which was studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and variable temperature powder X-ray diffraction (VT-PXRD). The studies revealed that both conjugated backbones and counteranions work together to organize the systems into different morphologies (liquid crystal/soft crystal). Dithieno[3,2-b:2',3'-d]phosphole-based compounds exhibit enhanced emission in the solid state and at low temperature in solution due to aggregation-induced enhanced emission (AIEE). Photoinduced electron transfer (PET) induced via the alkoxybenzyl group at the phosphonium center in the fused-ring systems can be effectively suppressed through intermolecular charge transfer (ICT) processes within the main scaffold of a nonfused system, which was confirmed by static and dynamic fluorescence spectroscopy. The dynamic features of these new materials also endow the systems with external-stimuli responsive photophysical properties that can be triggered by temperature and/or mechanical forces.
RESUMEN
The electrochemical and photophysical properties of a series of Ru(II) complexes related to [Ru(dcbpyH(2))(2)(ppy)](1+) (1; dcbpyH(2) = 4,4'-dicarboxy-2,2'-bipyridine; ppy = 2-phenylpyridine) were examined to elucidate the effect of modifying the anionic fragment of the C--N ligand with conjugated substituents (R). Included in this study is a family of compounds (2-5) consisting of one or two -NO(2) groups installed meta, ortho, and para to the organometallic bond. A suite of compounds with electron-donating and withdrawing groups (e.g., R = -F (6), -phenyl (7), -4-pyridine (8), -thiophene-2-carbaldehyde (9)) were also evaluated. Deprotonated forms of select compounds were isolated as tetrabutylammonium salts to benefit solution studies. All complexes were structurally characterized by a combination of mass spectrometry, (1)H and (13)C NMR spectroscopy, and/or elemental analysis. The electronic absorption spectra for all of the compounds reveal three broad bands over the 350-700 nm range. The maximum wavelength of the lowest energy absorbance bands for complexes modified with electron-withdrawing groups are hypsochromically shifted up to 45 nm relative to 1; the weakly emitting compounds (i.e., 1, 3, 6-9) display a hypsochromic shift of up to 63 nm compared to 1. Emission was not observed in cases where the -NO(2) group was positioned meta to the Ru-C bond. The sensitivity of the oxidation potentials to the nature, number, and position of the electron-withdrawing/-donating substituents for the entire set of compounds reflect a highest occupied molecular orbital (HOMO) character extended over the metal, the anionic portion of the C--N ligand, and, in the case of 7-9, the conjugated R group. The reduction potentials indicate that the lowest unoccupied molecular orbital (LUMO) is localized to the C--N ligand where R = -NO(2), and on the dcbpyH(2) ligands for all other compounds. This assessment was corroborated by time-dependent density functional theory (TD-DFT) studies.
RESUMEN
The effects of replacing a single polypyridyl ligand with an analogous anionic cyclometalating ligand were investigated for a set of three structurally related series of Ru(II) compounds formulated as [Ru(bpy)(2)(L)](z), [Ru(tpy)(L)](z), and [Ru(tpy)(L)Cl](z), where z = 0, +1, or +2, and L = polypyridyl (e.g., bpy = 2,2'-bipyridine, tpy = 2,2':6',2''-terpyridine) or cyclometalating ligand (e.g., deprotonated forms of 2-phenylpyridine or 3-(2-pyridinyl)-benzoic acid). Each of the complexes were synthesized and characterized by (1)H NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and/or elemental analyses (EA). Cyclic voltammetry reveals that cyclometalation causes a shift of the first oxidation and reduction potentials by -0.5 to -0.8 V and -0.2 to -0.4 V, respectively, relative to their polypyridyl congeners. These disparate shifts have the effect of inducing a bathochromic shift of the lowest-energy absorption bands by as much as 90 nm. With the aid of time-dependent density functional theory (DFT), the lowest-energy bands (lambda(max) = 500-575 nm) were assigned as predominantly metal-to-ligand charge-transfer (MLCT) transitions from Ru to the polypyridyl ligands, while Ru-->C(wedge)NN (or C(wedge)N(wedge)N or N(wedge)C(wedge)N) transitions are found within the absorption bands centered at ca. 400 nm. The properties of a series of compounds furnished with carboxylic acid anchoring groups at various positions are also examined for applications involving the sensitization of metal-oxide semiconductors. It is determined that the thermodynamic potentials of many of these compounds are appropriate for conventional photoelectrochemical cells (e.g., dye-sensitized solar cells) that utilize a titania electrode and iodide-based electrolyte.
RESUMEN
A divergence from the conventional approach to chromophore design has led to the establishment of many exciting new benchmarks for the dye-sensitized solar cell (DSSC), including the first documented power conversion efficiency in excess of 12% at 1 sun illumination [Yella et al., Science 2011, 334, 629]. Paramount to these advances is the deviation from polypyridyl ruthenium dyes bearing NCS(-) ligands, such as [Ru(dcbpy)(2)(NCS)(2)] (N3; dcbpy = 4,4'-dicarboxy-2,2'-bipyridine). While metal-free and porphyrin dyes have demonstrated much promise, the discovery that the NCS(-) ligands of N3 can be replaced by anionic, chelating cyclometalating ligands without compromising device efficiencies has ushered in a new era of ruthenium dye development. A particularly appealing feature of this class of dyestuff is that they offer acute control of the frontier molecular orbitals to enable the precise attenuation of both the ground and excited state redox potentials through judicious chemical modification of the aryl ring. This Perspective summarizes very recent developments in the field, and demonstrates how the new and rapidly expanding class of Ru-based sensitizers provides a conduit for enhancing the performance (and potentially the stability) of the DSSC.
RESUMEN
A cyclometalated Ru dye bearing two triphenylamine groups to augment light absorption exhibits a power conversion efficiency (PCE) in excess of 7% in the dye-sensitized solar cell despite having a large molecular footprint on TiO(2).
RESUMEN
We report the first case of Ru(II) dipyrrinates employed as dyes in dye-sensitized solar cells. These complexes exhibit panchromatic light harvesting that results in significant DSSC current densities, rendering them promising for photovoltaic applications. Adjustment of the lowest excited state energy is required to boost the power conversion efficiency.
RESUMEN
Analytically pure chloride and bromide salts of two different cyclic triphosphenium cations are prepared by the reaction of PX3 (X=Cl, Br) in the presence of the halogen-scavenging reagent cyclohexene. For the brominated species, the neutral, volatile 1,2-dibromocyclohexane byproduct is readily removed under reduced pressure, and the desired salts are obtained in high yield. Reactions involving phosphorus trichloride are complicated by the formation of salts containing both chloride and hydrogen dichloride anions. Reactivity experiments on potential undesired halogenated diphosphine byproducts suggest that the formation of such species can be prevented by increasing the concentration of cyclohexene employed in the reaction.