XANES and UPS studies of the UV photopolymerization of a diacetylene long chain compound in oriented evaporated films

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Abstract
The change of electronic structure at UV photopolymerization was studied by XANES and UPS for evaporated films of a long-chain diacetylene compound tricosa-10,12-diynoic acid. The UPS spectra showed a large lowering of ionization threshold energy (from 7.0eV to ca. 5.2eV) due to the formation of a conjugated π electron system, as in our previous study of Langmuir-Blodgett films. The XANES spectra showed that the alkyl chains are inclined to the substrate surface, consistent with X-ray diffraction studies. The Cls → π* absorption showed a drastic change on photopolymerization, which could be well explained with CNDO/S molecular orbital calculations taking account of the hole formation using the equivalent-core approximation. From XANES studies, no essential discontinuity was found between the blue and red forms of the polymers formed.