National Institute of Standards and Technology における超伝導研究及び生活

Occurrence, behavior and effects of nanoparticles in the environment.

In recent years, organic solar cells utilizing π-conjugated polymers have attracted widespread interest in both the academic and, increasingly, the commercial communities. These polymers are promising in terms of their electronic properties, low cost, versatility of functionalization, thin film flexibility, and ease of processing. These factors indicate that organic solar cells, although currently producing relatively low power conversion efficiencies (∼5-7%),1–3 compared to inorganic solar cells, have the potential to compete effectively with alternative solar cell technologies. However, in order for this to be feasible, the efficiencies of organic solar cells need further improvement. This is the focus of extensive studies worldwide. The backbone of a π-conjugated polymer is comprised of a linear series of overlapping pz orbitals that have formed via sp2 hybridization, thereby creating a conjugated chain of delocalized electron density. It is the interaction of these π electrons that dictates the electronic characteristics of the polymer. The energy levels become closely spaced as the delocalization length increases, resulting in a ‘band’ structure somewhat similar to that observed in inorganic solid-state semiconductors. In contrast to the latter, however, the primary photoexcitations in conjugated polymers are bound electron-hole pairs (excitons) rather than free charge carriers; this is largely due to their low dielectric constant and the presence of significant electron-lattice interactions and electron correlation effects.4 In the absence of a mechanism to dissociate the excitons into free charge carriers, the exciton will undergo radiative and nonradiative decay, with a typical exciton lifetime in the range from 100 ps to 1 ns. Achieving efficient charge photogeneration has long been recognized as a vital challenge for molecular-based solar cells. For example, the first organic solar cells were simple single-layer devices based on the pristine polymer and two electrodes of different work function. These devices, based on a Schottky diode structure, resulted in poor photocurrent efficiency.5–7 Relatively efficient photocurrent generation in an organic device was first reported by Tang in 1986,8 employing a vacuum-deposited CuPc/ perylene derivative donor/acceptor bilayer device. The differing electron affinities (and/or ionization potentials) between these two materials created an energy offset at their interface, thereby driving exciton dissociation. However, the efficiency of such bilayer devices is limited by the requirement of exciton diffusion to the donor/acceptor interface, typically requiring film thicknesses less than the optical absorption depth. Organic materials usually exhibit exciton diffusion lengths of ∼10 nm and optical absorption depths of 100 nm, although we note significant progress is now being made with organic materials with exciton diffusion lengths comparable to or exceeding their optical absorption depth.9–12 The observation of ultrafast photoinduced electron transfer13,14 from a conjugated polymer to C60 and the * To whom correspondence should be addressed. E-mail: j.durrant@ imperial.ac.uk. Chem. Rev. 2010, 110, 6736–6767 6736

Charge Photogeneration in Organic Solar Cells

Large polycyclic aromatic hydrocarbon (PAH) molecules carry the infrared (IR) emission features that dominate the spectra of most galactic and extragalactic sources. This review surveys the observed mid-IR characteristics of these emission features and summarizes laboratory and theoretical studies of the spectral characteristics of PAHs and the derived intrinsic properties of emitting interstellar PAHs. Dedicated experimental studies have provided critical input for detailed astronomical models that probe the origin and evolution of interstellar PAHs and their role in the universe. The physics and chemistry of PAHs are discussed, emphasizing the contribution of these species to the photoelectric heating and the ionization balance of the interstellar gas and to the formation of small hydrocarbon radicals and carbon chains. Together, these studies demonstrate that PAHs are abundant, ubiquitous, and a dominant force in the interstellar medium of galaxies.

Interstellar Polycyclic Aromatic Hydrocarbon Molecules

Mise au point. Theorie des effets de couplage vibronique multimodes. Probleme a 2 etats. Couplage vibronique mettant en jeu des modes et des etats degeneres. Effets du couplage vibronique multimodes en spectroscopie. Comportement statistique des niveaux d'energie vibroniques. Intersections coniques et evolution temporelle de la fluorescence

Multimode molecular dynamics beyond the Born-Oppenheimer approximation

A narrative account of the ingredients in the making of a young scientist, his wartime science in England, and subsequent career in France, where, starting in molecular electronic spectroscopy, he has grown older and has expanded his horizons to address problems of astrophysical, nonlinear optical, and biological interest, using, with the aid of many good scientists, a variety of techniques, mainly of optical and mass spectroscopies and with synchrotron radiation as an important excitation source. He has plans to continue.

IN MY TIME: Scenes of Scientific Life

Xenon Isotopic Composition in Acid Residues of EL Taco Inclusions

Vacuum UV photochemistry of gaseous SO2

Une augmentation de l'intensite de l'absorption triplet-singulet du benzene, vers 3 300 A, est observee en milieu liquide en presence d'oxygene. Discussion theorique de ce phenomene. En milieu rigide nous trouvons que la fluorescence et la phosphorescence (emission triplet-singulet) ne sont pas modifiees par la presence d'oxygene. Diverses hypotheses sont envisagees pour interpreter ce resultat. La necessite d'etudier l'absorption triplet-singulet en milieu rigide est soulignee.

Influence de l'oxygène et du tétrachlorure de carbone su r les spectres électroniques du benzène: I. — Effet d'oxygène

Recent laboratory studies of the electronic spectra and nonradiative relaxation properties of a number of singly-charged molecular cations are discussed Their interest for cometary physics is emphasized Spectroscopic and relevant cometary information is given on CS+, SH+, CO2 +, CS2 + and H2S+ Coincidence techniques have been used for studying radiationless transitions in CO2 +, NH3 + and other polyatomic ions The results have been amplified by the use of laser excitation methods in the case of CO2 + Some discussion is given on recent cometary observations of CO2 + emission The fluorescence quantum yields are measured for several molecular ions which could be formed from parent molecules likely to exist as frozen gases in the nucleus The possibility of spectral observation of these cations in comets is considered

Sydney Leach

Papers

IN MY TIME: Scenes of Scientific Life

Xenon Isotopic Composition in Acid Residues of EL Taco Inclusions

Vacuum UV photochemistry of gaseous SO2

Influence de l'oxygène et du tétrachlorure de carbone su r les spectres électroniques du benzène: I. — Effet d'oxygène

Electronic Spectroscopy and Relaxation of Some Molecular Cations of Cometary Interest