We present the femtosecond spectroscopic investigation of a covalently linked dyad, PCB-P3HT, formed by a segment of the conjugated polymer P3HT (regioregular poly(3-hexylthiophene)) that is end capped with the fullerene derivative PCB ([6,6]-phenyl-C61-butyric acid ester), adapted from PCBM. The fluorescence of the P3HT segment in tetrahydrofuran (THF) solution is reduced by 64% in the dyad compared to a control compound without attached fullerene (P3HT-OH). Fluorescence upconversion measurements reveal that the partial fluorescence quenching of PCB-P3HT in THF is multiphasic and occurs on an average time scale of 100 ps, in parallel to excited-state relaxation processes. Judging from ultrafast transient absorption experiments, the origin of the quenching is excitation energy transfer from the P3HT donor to the PCB acceptor. Due to the much higher solubility of P3HT compared to PCB in THF, the PCB-P3HT dyad molecules self-assemble into micelles. When pure C60 is added to the solution, it is incorporated into the fullerene-rich center of the micelles. This dramatically increases the solubility of C60 but does not lead to significant additional quenching of the P3HT fluorescence by the C60 contained in the micelles. In PCB-P3HT thin films drop-cast from THF, the micelle structure is conserved. In contrast to solution, quantitative and ultrafast (<150 fs) charge separation occurs in the solid-state films and leads to the formation of long-lived mobile charge carriers with characteristic transient absorption signatures similar to those that have been observed in P3HT:PCBM bulk heterojunction blends. While π -stacking interactions between neighboring P3HT chains are weak in the micelles, they are strong in thin films drop-cast from ortho-dichlorobenzene. Here, PCB-P3HT self-assembles into a network of long fibers, clearly seen in atomic force microscopy images. Ultrafast charge separation occurs also for the fibrous morphology, but the transient absorption experiments show fast loss of part of the charge carriers due to intensity-induced recombination and annihilation processes and monomolecular interfacial trap-mediated or geminate recombination. The yield of the long-lived charge carriers in the highly organized fibers is however comparable to that obtained with annealed P3HT:PCBM blends. PCB-P3HT can therefore be considered as an active material in organic photovoltaic devices.

Laser-ablated late lanthanide metal atoms were condensed with pure hydrogen at 4 K, and new infraredabsorptions are assigned to binary metal hydrides on the basis of deuterium substitution and density functionaltheory frequency calculations. The dominant absorptions in the 1330-1400 cm^-1 region are identified asLnH₃ complexes with very weak ligand bands near 3900 cm^-1. With ytterbium, YbH and YbH₂ were themajor initial products, but YbH₃ increased at their expense upon sample irradiation. Evidence is also presentedfor the LuH and ErH molecules and the tetrahydride anions in solid hydrogen.

The results of a combined spectroscopic and computational study of lanthanide hydrides with the general formula MH_x(H₂)_y, where M = La, Ce, Pr, Nd, Sm, Eu, and Gd, x = 1−4, and y = 0−6 are reported. To understand the nature of the dihydrogen complexes formed with lanthanide metal hydride molecules, we have first identified the binary MH_x species formed in the ablation/deposition process and then analyzed the dihydrogen supercomplexes, MH_x(H₂)_y. Our investigation shows that the trihydrides bind dihydrogen more weakly than the dihydrides and that the interaction between the central lanthanide and the H₂ molecules occurs via a 6s electron transfer from the lanthanide to the H₂ molecules. Evidence is also presented for the SmH and EuH diatomic molecules and the tetrahydride anions in solid hydrogen.

Laser-ablated Th atoms react with molecular hydrogen to give thorium hydrides and their dihydrogen complexes during condensation in excess neon and hydrogen for characterization by matrix infrared spectroscopy. The ThH₂, ThH₄, and ThH₄(H₂)_x (x = 1−4) product molecules have been identified through isotopic substitution (HD, D₂) and comparison to frequencies calculated by density functional theory and the coupled-cluster, singles, doubles (CCSD) method and those observed previously in solid argon. Theoretical calculations show that the Th−H bond in ThH₄ is the most polarized of group 4 and uranium metal tetrahydrides, and as a result, a strong attractive “dihydrogenâ€� interaction was found between the oppositely charged hydride and H₂ ligands ThH₄(H₂)_x. This bridge-bonded dihydrogen complex structure is different from that recently computed for tungsten and uranium hydride super dihydrogen complexes but is similar to that recently called the “dihydrogen bondâ€� (Crabtree, R. H. Science 1998, 282, 2000). Natural electron configurations show small charge flow from the Th center to the dihydrogen ligands.

The codeposition of laser-ablated tungsten atoms with neat hydrogen at 4 K forms a single major product with a broad 2500 cm^-1 and sharp 1860, 1830, 1782, 1008, 551, and 437 cm^-1 absorptions, which are assigned to the WH₄(H₂)₄ complex on the basis of isotopic shifts and agreement with isotopic frequencies calculated by density functional theory. This D_2d structured complex was computed earlier to form exothermically from W atoms and hydrogen molecules. Annealing the matrix allows hydrogen to evaporate and the complex to aggregate and ultimately to decompose. Comparison of the H−H stretching mode at 2500 cm^-1 and the W−H₂ stretching mode at 1782 cm^-1 with 2690 and 1570 cm^-1 values for the Kubas complex W(CO)₃(PR₃)₂(H₂) suggests that the present physically stable WH₄(H₂)₄ complex has more strongly bound dihydrogen ligands. Our CASPT2 calculations suggest a 15 kcal/mol average binding energy per dihydrogen molecule in the WH₄(H₂)₄ complex.

Several monouranium and diuranium polyhydride molecules were investigated using quantum chemical methods. The infrared spectra of uranium and hydrogen reaction products in condensed neon and pure hydrogen were measured and compared with previous argon matrix frequencies. The calculated molecular structures and vibrational frequencies were used to identify the species present in the matrix. Major new absorptions were observed and compared with the previous argon matrix study. Spectroscopic evidence was obtained for the novel complex, UH₄(H₂)₆, which has potential interest as a metal hydride with a large number of hydrogen atoms bound to uranium. Our calculations show that the series of complexes UH₄(H₂)_1,2,4,6 are stable.