Formation of the newly greenish organized molecular film of long-chain diynoic acid derivatives by photopolymerization and its structural study using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy

The effect of molecular arrangements with annealing on photopolymerization in the Langmuir-Blodgett films of 10,12-pentacosadiynoic acid cadmium salt was investigated using UV-vis spectroscopy, out-of plane and in-plane X-ray diffraction (XRD), and polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The formation of a greenish polymer film with an extended conjugate system was determined to be related to the film structures. Furthermore, the incident-angle dependence of C1s-pi* transition peaks on the annealed transferred film with an extended conjugate system was confirmed by C K-edge polarized NEXAFS spectroscopy, whereas this dependency was not observed on nonannealed multilayer films. In addition, multilayers of metal-free 10,12-pentacosadiynic acid were examined by photopolymerization, and their film structures were elucidated. Contrary to expectations, a red-colored polymer film was observed to form highly ordered side-chain orientations with the shift of the C1s-pi* transition peaks in the NEXAFS spectra, although the regularity of molecular and side-chain arrangement for monomer and blue polymer films could not be confirmed. These findings indicate the color phase transition of diacetylene derivatives with photopolymerization induced the rearrangement of the conjugated backbone, supported by a shift of the C1s-pi* band in the NEXAFS spectra.