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Multiple exciton generation (MEG) and exciton recombination were studied by femtosecond transient absorption spectroscopy in PbS nanoparticles (NPs) capped with oleic acid (PbS-OLA) and 2,3-dimercaptopropane sulfonate (PbSDMPS) ligands. Analysis of the transient absorption data showed that the PbS-DMPS nanoparticles exhibit increased rates of multi- and single-exciton recombination compared with the PbS-OLA nanoparticles; however, the MEG yield for both sets of particles was the same within experimental error. The origin of the differences in the exciton recombination decay rates is unknown, but it is speculated that it may be due to the ionic functionality of DMPS or to the different ligating atoms of the OLA and DMPS ligands. The PbS-DMPS nanoparticles were highly sensitive to the presence of oxygen, which caused a dramatic increase in nonradiative decay pathways, which can be mistaken for multiexciton absorbance and decay. Removal of oxygen eliminated the nonradiative decay pathways. Overall, this study showed that the dynamics of MEG can be modified by changing the NP ligand shell, a result that may be useful in the development of NP-based thin-film solar devices. Key words: multiple exciton generation, surface modification of nanoparticles, exciton recombination, nanoparticle ligand exchange. On a etudie le generation d'excition multiple (GEM) et la recombinaison d'exciton par spectroscopie d'absorption des especes transitoires au niveau de la femtoseconde, dans des nanoparticules de PbS coiffees de ligands d'acide oksque (PbS-OLA) et de sulfonate de 2,3-dimercaptopropane (PbS-DMPS). L'analyse des donnees d'absorption des especes transitoires montre que, par comparaison avec les nanoparticules de PbS-OLA, les nanoparticules de PbS-DMPS presentent des vitesses accrues de recombinaison d'excitons simples et multiples; toutefois, les rendements pour la GEM sont les memes, aux erreurs experimentales pres, dans les deux cas. L'origine des differences dans les vitesses de decroissance de recombinaison de l'exciton est inconnue, mais il est possible de speculer qu'elle pourrait etre due a la fonctionnalite ionique du DMPS ou aux atomes de ligature differents des ligands OLA et DMPS. Les nanoparticules de PbS-DMPS sont tres sensibles a la presence d'oxygene qui provoque une augmentation dramatique dans les voies non radiatives de decroissance, que l'on peut attribuer a tort a de l'absorbance multiexciton et a de la decroissance. L'enlevement de l'oxygene permet d'eliminer ces voies de decroissance non radiatives. Dans l'ensemble, cette etude montre que la dynamique de la GEM peut etre modifiee par un changement de la couche de ligand de nanoparticules, un resultat qui peut etre utile dans le developpement de dispositifs solaires en film mince a base de nanoparticules. Mots-cles: generation d'excition multiple, modification de la surface de nanoparticules, recombinaison d'exction, echange de ligand d'une nanoparticule., Introduction Semiconductor nanoparticles (NPs) are favorable candidates for integration into cost-effective solar devices. This is primarily due to their broad optical tunability and ease of processing. In particular, lead chalcogenide [...]

Several methods are employed to find out if there exists a spin barrier to the recombination of the first- and second-row transition metal-centered radicals in a radical cage pair, which are normally photochemically generated. The techniques used proves that no heavy atom effects take place, which then finally helps in concluding that the recombination doesnEt have to actually face any kind of spin barrier.

Research has been conducted on 1,2-bis(bis(hydroxyalkyl)phosphino)ethanes. The reactions of these water-soluble chelating phosphines with FeCl (sub)2 .4H (sub)2 O have been investigated and the results indicate that the transition metal compound stereochemistry depends on the phosphine's solvent, alkyl chain length and counteranion.

Research has been conducted on the epimeric carbohydrate alkyl cobaloximes. The photochemical and thermal epimerization of epimeric cobaloxime pairs has been performed and the results are described.

Research is presented concerning the aqueous chemistry of the demeric molybdocene complex on organometallic catalysis in water. The activation of the C-H bond when catalytic H/D exchange occurs is discussed.

Temperature-dependent electron paramagnetic resonance spectra of four metal complexes of 2,3-bis(diphenylphosphino)maleic anhydride (BMA), the ligand radical anion, [BMA]-(6-) and the radical anion of the related compound 4,5-bis(diphenylphosphino)cyclopentene-1,3-dione are described. It was observed all spectra are 1:2:1 triplets due to hyperfine coupling to one or two 59Co nuclei for the Co complexes with chelating or bridging BMA at room temperature. It was also observed that the 31P couplings are temperature-dependent for the metal complexes and ligand radical anions.

Density functional calculations of the anisotropic hyperfine coupling constants for a 19-electron organometallic complex, CpCo(CO)2- were performed using the B2LYP density functional in conjunction with various all-electron basis sets. Results suggest that the traditional method of calculating atomic orbital spin populations from electron paramagnetic resonance hyperfine coupling constants should be used cautiously when applied to organometallic systems.

Organometallic photochemistry is used in the deposition of thin films, initiation of cationic and radical polymerization reactions and derivatization of surfaces. These applications use the characteristics of different excited states generated by photoreactions, including ligand field excited states and charge-transfer transitions. Metal-ligand bond dissociation is used in surface derivatization. The reaction mechanisms and principles are described.

The reaction of olefinic alcohols with 1,2-bis(phosphino)ethane in a free-radical environment produced hydroxybutyl and hydroxypentyl homologs of 1,2-bis(bis(hydroxymethyl)phosphino)ethane. The synthesis of the 1,2-bis(bis(hydroxyalkyl)phosphino)ethane ligands is characterized by the free radical addition of 1,2-bis(phosphino)ethane to 3-buten-1-ol(Aldrich) olefin alcohol. Furthermore, the ligands react with Ni(II), Ru(III), and Rh(I) to form transition metal complexes that exhibit water solubility.

The synthesis and characterization of 19-electron complexes are described. The scheme involves disproportionation of (CpCH2CH2NH3+ sub2 Mo2 CO sub6) (NO3-)2 and reduction of methyl viologen to establish the formation of the target adducts from 1,2-bis(dihydoxymethylphosphino ethane). The X-ray crystal structure of the (HOCH2)2PCH2CH2P(CH2OH)2 ligand of its complex Ni(dhmpe)2(Cl2) were also determined.