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

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 n 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 CIS + n* absorption showed a drastic change on photopolymerization, which could be well explained with CNDOjS 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.

Soft X-ray Absorption and X-ray Photoelectron Spectroscopic Study of Tautomerism in Intramolecular Hydrogen Bonds of N-Salicylideneaniline Derivatives

“…The similarity of their spectra with those of NPY and MBAF with a single tautomeric part indicates only weak interaction. This was also confirmed by CNDO/S MO calculations of BSP, NPY, and DNP using equivalent core approximation − at the N K - and O K -edges.…”

NEXAFS study of a 17,19-hexatriacontadiyne monolayer on Au(111)

“…The energy of the localized p à k MO exists around the top of the lower p * band and the r à CC MO appears at a higher energy region [42] (Note that the r à C@C resonance is observed at 301 eV in the spectrum of an ethylene multilayer on Si(1 0 0) [41]). Though two separated peaks corresponding to the bottom of the p * bands and the localized p à k MOs are observed in the NEXAFS spectra of PDs in SAMs and most LB films [32][33][34], this is not the case for the irradiated HTDY monolayer on Au (1 1 1).…”

“…This is different from a situation for the p * resonance of other diacetylenes showing two peaks in the spectra: since the electron density is different for the inner and outer carbons of the C"CAC"C moiety, the extent of core-hole screening by electrons and the energy of the C 1s ! p * transition are different for these carbons as well [32][33][34]. Owing to this effect, two peaks separated by 0.6-1.2 eV are observed in most cases [32][33][34], and there seems no simple reason to reduce the difference of the screening effect in the HTDY multilayer.…”

“…p * transition are different for these carbons as well [32][33][34]. Owing to this effect, two peaks separated by 0.6-1.2 eV are observed in most cases [32][33][34], and there seems no simple reason to reduce the difference of the screening effect in the HTDY multilayer. Hence, the peak is interpreted as the convolution of two peaks at 285.7 and 286.2 eV, although some ambiguity is included in the deconvolution procedure.…”

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

“…However, it was later suggested, based on the results of UPS measurements, that both the blue and red polymers formed the acetylenic structures. 18,20 A slight fluctuation the hydrocarbon side-chain packing is currently considered to be the cause of these color phase transitions with UV irradiation, thermal treatment, or exposure to organic solvents, although the change in the detailed electronic state is not clear. Recently, the diacetylene monomer-to-polymer conversion efficiencies in the films were measured by fluorescence yield near-edge spectroscopy (FYNES) in the C1s-π* region (280-286 eV).…”