Interfacial Charge-Transfer Switch: Ruthenium−dppz Compounds Anchored to Nanocrystalline TiO2

Effect of pH in the photoluminescence of a ruthenium complex featuring a derivative of the ligand pyrazine[2,3-f][1,10]-phenanthroline

A new ruthenium complex, [Ru(bpy)2(dbe-ppl)](PF6)2 (bpy=2,2'-bipyridine and dbe-ppl=dimethyl 4,4'-(pyrazino[2,3-f][1,10]phenanthroline-2,3-diyl)dibenzoate, has been synthesized and characterized by (1)H NMR spectroscopy, UV-Vis, IR, and cyclic voltammetry. Irradiation on the MLCT band results in photoluminescence in both protic and aprotic solvents. The photoluminescence in water is pH dependent, it shows a behavior which can be described by the Henderson-Hasselbalch assuming the protonation/deprotonation of the excited state with a pKa of 2.40±0.01.

Long-wavelength sensitization of TiO2 by ruthenium diimine compounds with low-lying π* orbitals

The role of low-lying π* orbitals in dye-sensitized solar cells based on mesoporous thin films of anatase TiO(2) nanocrystallites remains unknown. Herein we report three ruthenium compounds, cis-Ru(dcbq)(2)(NCS)(2), cis-Ru(dcbq)(bpy)(NCS)(2), and cis-Ru(dcb)(bq)(NCS)(2), where bpy is 2,2'-bipyridine, dcb is 4,4'-(CO(2)H)(2)-2,2'-bipyridine, bq is 2,2'-biquinoline, and dcbq is 4,4'-(CO(2)H)(2)-2,2'-biquinoline, that were synthesized, characterized, and contrasted with the well-known N3 compound (i.e., cis-Ru(dcb)(2)(NCS)(2)) in dye-sensitized solar cells. These compounds maintain the same cis-Ru(NCS)(2) core with a systematic variation in the energy of the π* orbitals of the diimine ligand: bpy > dcb > bq > dcbq. The lowered π* orbitals resulted in enhanced red absorption relative to N3. With HCl pretreated TiO(2) in regenerative solar cells, sensitization from 400 to 900 nm was realized with cis-Ru(dcb)(bq)(NCS)(2) and global power conversion efficiencies as high as 6.5% were achieved under 1 sun of AM 1.5 irradiation. The energy conversion efficiency was found to be acutely sensitive to the presence of p-tert-butylpyridine (TBP) in a 0.5 M LiI/0.05 M I(2) acetonitrile electrolyte. Nanosecond transient absorption studies revealed that the addition of TBP decreased the excited-state injection yield for the compounds with biquinoline ligands. Spectro-electrochemical studies showed that the HCl pretreatment lowered the effective density of TiO(2) acceptor states and confirmed that the presence of TBP raised them toward the vacuum level. There was no spectroscopic data to support the hypothesis that the π* levels of the diimine ligand mediate back-electron transfer to the oxidized dye or the redox mediator was found.

Boron polylactide nanoparticles exhibiting fluorescence and phosphorescence in aqueous medium

Difluoroboron dibenzoylmethane-polylactide, BF(2)dbmPLA, a biocompatible polymer-luminophore conjugate was fabricated as nanoparticles. Spherical particles <100 nm in size were generated via nanoprecipitation. Intense blue fluorescence, two-photon absorption, and long-lived room temperature phosphorescence (RTP) are retained in aqueous suspension. The nanoparticles were internalized by cells and visualized by fluorescence microscopy. Luminescent boron biomaterials show potential for imaging and sensing.

Quenching of luminescent ruthenium(II) complexes by water and polymer-based relative humidity sensors

Water quenching of luminescent [Ru(phen)(2)dppz]Cl(2), [Ru(phen)(2)dppn]Cl(2), and [Ru(4,7-Ph(2)phen)(2) dppz]Cl(2) (phen = 1,10-phenanthroline; 4,7-Ph(2)phen = 4; 4,7-diphenyl-1,10-phenanthroline; dppz = dipyrido[3,2-a:2'3'-c]phenazine; dppn = benzodipyrido(a:3,2-h:2',3'-j)phenazine) complexes was studied in acetonitrile and in polymers. The polymers contained hydrophobic and hydrophilic components to control mechanical properties and were designed to absorb water with changing humidity and, thus, affect the emission intensity and lifetime. Quenching by water in mixed solvents and in polymers was shown to arise from a combination of diffusional and static ground-state associational quenching. The factors controlling polymer properties are discussed. The systems can be tailored to give a wide range of responses or function as a binary sensor at a fixed humidity level.

Monolayer-Based Selective Optical Recognition and Quantification of FeCl3 via Electron Transfer

Reagentless optical recognition and parts-per-million (ppm) quantification of FeCl3 in CH3CN was demonstrated using a redox-active Os(II)-chromophore-based monolayer on glass. The Fe3+-induced oxidation of the monolayer is fully reversible and can be monitored optically with a conventional UV/vis spectrophotometer (260-800 nm). The system can be reset with water within <1 min. Selectivity of the sensor toward FeCl3 is not affected by the presence of representative alkali metals, alkaline earth metals, and other transition-metal salts. Sensing of Fe3+ and concurrent generation of Fe2+ can be also observed with the naked eye by adding 2,2'-bipyridyl (bipy) to the solution to generate [Fe(bipy)3]2+. Validation of the analytical performance characteristics of the sensor was performed including reversibility, reproducibility, stability, and the detection range (0.5-162 ppm of FeCl3 in CH3CN, 100-1000 ppm in water). The monolayer is sensitive and specifically responsive to its target ion. In addition, a blind test was conducted to probe the reproducibility and reproducibility variances of the system. The reaction of the monolayer with a CH3CN solution containing 5 ppm of FeCl3 follows pseudo first-order kinetics in the monolayer with DeltaG298K = 21.6 +/- 0.1 kcal/mol, DeltaH = 10.2 +/- 1.5 kcal/mol, DeltaS = -38.3 +/- 4.9 eu.