An aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) combined with a thermodenuder (TD) was used to investigate laboratory-generated aerosol particles with regard to their volatility and chemical content. The performance of the setup was tested first by using ammonium sulfate particles. Organic compounds have been measured including humic acid, fulvic acid, succinic acid and its disodium salt, 2-methylsuccinic acid, fumaric acid, alpha-ketoglutaric acid, and glutaric acid. Among them, humic acid, fulvic acid, and disodium succinate show a non-volatile fraction at 300 degrees C, while the other organic compounds are more volatile. Comparisons of mass spectra at different temperatures showed that significant differences in mass spectra of humic and fulvic acids are observed, indicating that their molecules changed during or after volatilization. At lower temperatures, the changes in humic acid are more likely due to the evaporation of small organic molecules or decomposition of aliphatic groups. The mass losses of the CO(2)(+) fragment for both humic and fulvic acids at higher temperatures may arise from decarboxylation processes. The different mass spectra for humic and fulvic acids before and after TD also suggest that one should be careful in interpretation of volatility measurements because some molecule structures may change after being heated, especially for the non-volatile multifunctional compounds. (C) 2009 Elsevier Ltd. All rights reserved.
Dimeric and trimeric molecules comprising perylenediimide units conjugatively linked by phenylene, ethynylene, or a butadiynylene spacer via the bay positions were prepared. Electrochemical and photophysical characterizations showed that oligomers connected by C-C triple bond(s) exhibited effectively lowered LUMO compared to the monomer. Molecular modeling confirmed that the C-C triple bond realized efficient delocalization of frontier orbitals, while phenylene was less competent in extending the conjugation, partially due to steric interactions.