PUB - Publikationen an der Universität Bielefeld

The S-1 -> S-0 radiationless deactivation of iodine terminated bi-phenyl immobilized on a silicon surface was probed by analysing the I4d signature (BE: 45.6 eV, 47.3 eV) by means of High Harmonic Generation (HHG) based photoelectron spectroscopy. Modifications of the 4d(5/2,3/2) spectroscopic contents spanning about 0.2 ps after UV activation (266 nm) were verified as showing a transient molecular response character. A localization to the terminated phenyl substructure in the complex structural environment on the surface was ensured according to the core-level nature of the recorded I4d. The activation of the bi-phenyl achieved by UV irradiation, corresponding to the UV absorption band-edge, was verified as being dominated by a B pi -> B pi* phenyl excitation. Time-Dependent Density Functional Theory (TD-DFT) modellings were therefore performed. They were matched to Configuration Interaction semi-empirical calculations (CI-MNDO) verifying the Rustagi-Ducuing relation. The simulated singlet-singlet excitation spectrum was referenced to the spectra of an iodine terminated monomer and a linear oligophenyl chain (N=8). Thus the deactivation response studied was assigned to a conical intersection promoted S-1(pi*)-> S-0(pi) reaction pathway.