Photopolymerization of long-chain diacetylene monocarboxylic acid in Langmuir-Blodgett films studied by UV photoelectron spectroscopy and X-ray absorption near-edge structure

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 splitting of each peak is due to the difference in the effect of the core hole created between excitations from the inner and outer carbons of the -C≡C-C≡C-unit. 15,19,43 However, the splitting of C1s-π* transition peaks was not confirmed in the cadmium salt film in this study. Therefore, the inner and outer carbons of the diacetylene functional group in the LB film for diynic acid cadmium salt were determined to be almost equivalent.…”

Changes in the near‐edge X‐ray absorption fine structure spectra of long‐chain diacetylene derivatives through photopolymerization in Langmuir–Blodgett films

“…Figure 3(A,B) presents an analysis of the curve fitting for the C K‐edge NEXAFS spectra at the magic angle (55° = 90 − θ, where θ is the X‐ray incidence angle) for a preannealed CdDA[11‐8] monomer LB film and a blue PCdDA LB film; the intensities of the spectra depend strongly on the incident angle. Each band could be assigned to transitions from C1s to π*(CC) at 285.5 eV, σ*(CH) at 287.6 eV, π*(CO) at 288.4 eV, and σ*(CC) at 292.6 eV,13, 18 as summarized in the table. Recently, a study of soft X‐ray fluorescence spectroscopy of C1s–π* bands for PDA at a lower photon energy of approximately 283–286 eV was reported in detail 14…”

“…The peak at 285.9 eV represents the C1s–π*(CO) transition of the carboxyl group for the DA[11‐8] anion dimer (COO − … − OOC) because this peak was only slightly shifted with the polymerization or color phase transition; a shift in this region was not observed in previous studies using evaporated diynic acid derivative films or LB films of cadmium salts 12, 19. The splitting of the C1s–π*(CC) and C1s–π*(CC) bands primarily affected the π–π interactions of the polymerizable functional groups for the DA[11‐8] monomers, and this affected the molecular packing in the monomer multilayers 13, 18, 20. The molecular orientation of the CdDA[11‐8] monomers was controlled by the LB method, and molecular packing mainly occurred through hydrocarbon‐chain/hydrocarbon‐chain interactions.…”

“…The relative intensities were corrected for the variations of the incident angles and the reduction of the ring current, and they were normalized with respect to the edge jump of the transition to the continuous state (290.5 eV) in the region of higher energy than the vacuum level. The NEXAFS spectra were fitted with several Gaussian functions from lower photon energy to high photon energy, and each band was assigned by reference to literature values 13, 18. Photopolymerization was carried out through the exposure of the films to a 500‐W xenon lamp at a distance of 40 cm.…”

“…Previously, the polymerization of amphiphilic monomers, such as long‐chain vinyl esters and long‐chain diynoic acid, was found to be considerably accelerated, and the structures of the resultant polymers could be controlled in LB films 10, 11. With ultraviolet (UV) photoelectron spectroscopy and near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy of the photopolymerization of a long‐chain DA derivative in LB films, a delocalized π* band was clearly observed, and the ionization threshold energy was found to be reduced by 1.6 eV from 6.7 (monomer) to 5.1 eV (polymer), regardless of the polymer color; this suggested that the color phase transition was induced by a slight distortion of the electronic structure of the acetylene polymer, which seemed to be strongly correlated to changes in the lattice structures of the side chains 12, 13. Recently, the DA monomer‐to‐polymer conversion efficiencies in films were measured with fluorescence yield near‐edge spectroscopy in the C1s–π* region (280–286 eV) 14…”