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Articles you may be interested inCorrelation between oxygen adsorption energy and electronic structure of transition metal macrocyclic complexes J. Chem. Phys. 139, 204306 (2013) In order to obtain a better understanding of the role of conformational disorder in the photophysics of conjugated polymers the ultrafast transient absorption anisotropy of partially deconjugated MEH-PPV has been measured. These data have been compared to the corresponding kinetics of Monte Carlo-simulated polymer chains, and estimates of the energy hopping time and energy migration distances for the polymers have been obtained. We find that the energy migration in the investigated MEH-PPV is approximately 3 times faster than in previously studied polythiophenes. We attribute this to a more disordered chain conformation in MEH-PPV.

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Long wavelength UVA1 (340-400 nm) is the main component of terrestrial UVR and is increasingly used in skin phototherapy. Its damage to critical biomolecules such as DNA has been widely attributed to its ability to generate reactive oxygen species (ROS) via other chromophores. However recent studies in vitro and in vivo have shown that UVA1 has a specific ability to generate cyclobutane pyrimidine dimers (CPD), especially thymine dimers (T<>T), and that this is probably due to direct absorption of UVR. The CPD has been implicated in many aspects of skin cancer. Measuring UVB-induced CPD in the epidermis and dermis in vivo shows that, as expected, the skin attenuates UVB. In contrast, our data show that this is not the case with UVA1: in fact there is more damage with increased skin depth. This suggests that the basal layer, which contains keratinocyte stem cells and melanocytes, is more vulnerable to the carcinogenic effects of UVA1 than would be predicted by mouse models. These data support the continuing trend for better UVA1 protection by sunscreens.

Electronic absorption and resonance Raman spectra of the radical cation of bithiophene are reported. The bithiophene radical cation was produced by γ-radiolysis in a glassy matrix at 77 K, and the Raman spectrum excited in resonance with the two absorption bands at 425 and 590 nm. The electronic states relevant to the observed electronic transitions were identified and characterized by CASSCF calculations. The optical absorption and resonance Raman spectra were calculated by wave packet propagation methods using the ab initio calculated molecular parameters. The calculated spectra agree well with the experimental ones. The importance of carrying out full wave packet propagation calculations is underlined by the fact that in one case the simple Savin formula gave a completely wrong prediction of the resonance Raman spectrum.