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

Transmembrane electron transport mediated by photoexcited fullerenes

On a etudie a faible et a moyenne resolution spectrale le spectre d’emission obtenu en excitant l’oxysulfure de carbone par un faisceau d’electrons d’energie 120 eV.Les observations spectroscopiques principales sont les suivantes :Spectre A : Un systeme de 10 bandes entre 3 180 A et 4 320 Â formant 5 groupes de doublets, l’ecart entre les composantes des doublets est de l’ordre de 250 cm-1 .Spectre B: des bandes de plus faible intensite dans la meme region spectrale.Spectre C : Un tres grand nombre de raies fines entre 4 000 A et 6 500 A. Les spectres B et C ne montrent pas de structure evidente.L’etude de la structure de vibration observee, et un calcul theorique des constantes de couplage spin-orbite des differents etats electroniques de l’ion COS+ , ont permis d’attribuer le spectre A a l’ion COS+ . La transition est tres probablement A2 II — X2 II et la vibration principale excitee est v"3 . Les bandes 3183 A-3 209 A forment l’origine du systeme A, elles ne sont cependant pas les bandes les plus intenses de ce systeme. L’ensemble des resultats experimentaux est en accord avec une analyse theorique de la structure electronique de l’ion COS2 + , faite par la methode des orbitales moleculaires. La validite des methodes theoriques utilisees a ete confirmee par une etude parallele sur l’ion CO2 + .

Spectre d’émission de cos+

Fluorescence and phosphorescence spectroscopy of C70 in toluene at 5 K: site dependent low lying excited states

Coupling a dendrimer and a fullerene chromophore: a study of excited state properties of C61(poly(aryl)acetylene)2

VUV photodissociation of gaseous acetic acid was studied in the 6–23 eV range using synchrotron radiation excitation, photofragment fluorescence spectroscopy and mass spectrometry. OH (A-X), CH (A,B-X) and H-Balmer emissions were observed. Their relative intensities were studied by fluorescence excitation spectroscopy. The fluorescence quantum yield for OH emission has a maximum of 0.9% at 13.3 eV photoexcitation, dropping to 0.5% at 20 eV; that for CH (A-X) is 0.35% at 16 eV and 0.4% at 20 eV. Photoionization mass spectra (PIMS) of CH 3 COOH were measured and the appearance energies of the principal photoions were determined. IE(CH 3 COOH) = 10.58 ± 0.02 eV is 40–60 meV lower than previous PIMS values. Dissociative ionization reaction channels are discussed in detail. The results call into question previous determinations of the heat of formation and ionization energy of the acetyl radical. A new pathway is suggested for the formation of HCO + , and the assignments of the m / z  = 16, 28 and 31 ions are clarified. The formation of CH 3 + at threshold is shown to involve carbon–carbon bond rupture and a potential energy barrier. The results of this study are used to discuss aspects of astrophysical observations involving the parent and fragment species.

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Sydney Leach

Papers

Transmembrane electron transport mediated by photoexcited fullerenes

Spectre d’émission de cos+

Fluorescence and phosphorescence spectroscopy of C70 in toluene at 5 K: site dependent low lying excited states

Coupling a dendrimer and a fullerene chromophore: a study of excited state properties of C61(poly(aryl)acetylene)2

VUV photophysics of acetic acid: Fragmentation, fluorescence and ionization in the 6–23 eV region