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Toluene-X van der Waals clusters (where X=Ne, Ne2, Ar, Ar2, Kr, Xe) have been investigated by fluorescence excitation spectroscopy in the region of the S1-S0 transition. With the exception of Xe, for each rare-gas studied, we have assigned cluster transitions in the region of all the strong monomer vibrational bands up to 1000 cm-1 above the origin band. We have further investigated the S1 relaxation dynamics for each vibrational level of each complex, via their fluorescence decay profiles. Clustering with neon has little appreciable effect on the vibrationless S1 lifetime. By contrast, the clusters with argon and krypton exhibit markedly shorter fluorescence lifetimes compared with the monomer. The effect is so severe in the case of toluene-Xe clusters that no fluorescence signals were observed. We interpret these results in terms of an external heavy atom effect in which the rate of intersystem crossing in toluene is influenced by the cluster partner. For clusters built upon excited S1 vibrational levels, the situation is potentially complicated by intramolecular vibrational redistribution and vibrational predissociation (VP). The majority of the fluorescence decay profiles were satisfactorily modeled using single exponential decays. The emission following pumping of the 371 level in the toluene-Kr cluster, however, is an exception. We have modeled the decay of this level with a simple kinetic scheme including VP and determined a predissociation rate of (1.04±0.54) × 107 s-1. [ABSTRACT FROM AUTHOR]

We present a combined experimental and computational study of the external heavy atom effect in van der Waals clusters of para-difluorobenzene (pDFB) with rare-gas atoms. Experimentally, clustering with rare-gas atoms is observed to shorten significantly the S1 fluorescence lifetime compared with that of the pDFB monomer, an effect we interpret in terms of an enhancement of the S1-T1 intersystem crossing rate. In order to test the validity of this widely held assumption, we have calculated the S1-T1 spin–orbit coupling matrix elements in the X-pDFB complexes (X=Ne,Ar,Kr) using a multiconfigurational linear response approach. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Low power electronics are an ideal application for organic photovoltaics (OPV) where a low-cost OPV device can be integrated directly with a battery to provide a constant power source. We demonstrate ultra-high voltage small molecule multijunction devices with open circuit voltage ( VOC) values of up to 7V. Optical modelling is employed to aid the optimisation of the complex multi-layer stacks and ensure current balancing is achieved between sub-cells, and optimised multijunction devices show power conversion efficiencies of up to 3.4% which is a modest increase over the single junction devices. Sub-cell donor/acceptor pairs of boron subphthalocyanine chloride (SubPc)/fullerene (C60) and SubPc/Cl6-SubPc were selected both for their high VOC in order to minimise the required number of junctions, but also for their absorption overlap to reduce the spectral dependence of the device performance. As a result, the devices are shown to directly charge a micro-energy cell type battery under both low illumination intensity white light and monochromatic illumination. [ABSTRACT FROM AUTHOR]

The change in profile of crude oil following a release into the environment is a topic of significant interest, and there is a need to develop analytical methodologies for understanding natural processes which affect related complex mixture profiles. One such process is the exposure to sunlight. In the following investigation, three oil samples were studied: one served as a control, a second was subjected to irradiation by an ultraviolet lamp, and a third sample was irradiated by a SoLux light source which closely models the solar emission profile. The usage of the SoLux light source represents a new method which enables a controlled experiment to mimic the effects of sunlight upon the sample. Atmospheric pressure photoionization was selected as the primary ionization method due to the ability to ionize a broad range of compounds, including low polarity components which could not be observed using electrospray ionization. During a test of sample preparation methods, the addition of a protic cosolvent to the sample solutions was shown to broaden the range of heteroatom-containing components observed. Following characterization, it was found that the polyaromatic hydrocarbons did not change in profile, while compounds containing a heteroatom exhibited a tendency to oxidize following photoirradiation. Sulfur-containing compounds with a low number of double bond equivalents were among the most reactive components of the complex mixture. The photooxidation of compounds in petroleum, following exposure to sunlight, is expected to have significance with regards to solubility and potential toxicity.