Volume 126, Issue 18, 14 May 2007
Index of content:
Excited state calculations on fluorene-based polymer blends: Effect of stacking orientation and solvation126(2007); http://dx.doi.org/10.1063/1.2732341View Description Hide Description
Polyfluorene-based polymer blends have been utilized in the development of optoelectronic devices. The constituent copolymers are chemically designed to facilitate more efficient electron/hole mobility, thereby enhancing control over exciton formation and dissociation. When appropriate pairs of these are blended together, intermolecular charged-particle localizations are induced, leading to significant intermolecular charge-transfer character and luminescence that exhibit some sensitivity to their interfacial orientation. The authors report on a time-dependent density functional theory quantum chemical investigation of the relevant excited states of the polymer blend poly[9,9-dioctylfluorene-co--(4-butylphenyl)diphenylamine]/poly(9,9-dioctylfluorene-co-benzothiadiazole. They show that the calculated excited states generally agree with experimental observations although there is a consistent underestimation of the charge-transfer states. Further, they show sensitivity to lateral shifts in interfacial stacking. Finally, solvation with a low dielectric solvent greatly stabilizes the charge-transfer states.
Ab initio simulation of a gadolinium-based magnetic resonance imaging contrast agent in aqueous solution126(2007); http://dx.doi.org/10.1063/1.2736369View Description Hide Description
The first ab initiomolecular dynamics simulation of a Gd(III)-based contrast agent in explicit aqueous solution at ambient conditions as used in the actual magnetic resonance imaging of human bodies is presented. The description of the structure of this chelate complex is considerably improved with respect to typical force fields and ab initio calculations in continuum solventmodels if the open shell of Gd is included explicitly. The solvation-shell structure is revealed to be anionic and includes a rather short hydrogen bond donated by the hydroxypropyl arm.
126(2007); http://dx.doi.org/10.1063/1.2739504View Description Hide Description
The isothermal crystallization process of thin amorphous solid water (ASW) films on Ru(0001) has been investigated in real time by simultaneously employing helium atom scattering, infrared reflection absorption spectroscopy, and isothermal temperature-programmed desorption. The measurements reveal that the crystallization mechanism consists of random nucleation events in the bulk of the ASW films, followed by homogeneous growth. Morphological changes of the solid water film during crystallization expose the water monolayer just above the substrate to the vacuum during the crystallization process.