Raman Microspectroscopic Study on Polymerization and Degradation Processes of a Diacetylene Derivative at Surface Enhanced Raman Scattering Active Substrates. 2. Confocal Raman Microscopic Observation of Polydiacetylene Adsorbed on Active Sites

Abstract

Confocal Raman microscopic measurements were performed at room temperature on the Langmuir-Blodgett (LB) monolayer of 10,12-pentacosadiynoic acid (DA) prepared on surface enhanced Raman scattering (SERS) active Ag island films, two-dimensional (2D) Raman images of which exhibit bright and dim spots on a dark background. The measurements performed by focusing the excitation laser light (488 nm) on the dark background indicate the prompt appearance of the Raman bands (1515 and 2115 cm(-1)) due to polydiacetylene (PDA) in the red phase and subsequent diminution of the Raman bands. On the other hand, the spectra observed by focusing the excitation laser spot on the dim and bright spots exhibit almost random fluctuations, giving rather narrow Raman bands in the 1620-1000 cm(-1) region, which appear and disappear temporarily with varying intensities under the continuous irradiation at 488 nm. Broad Raman bands appear around 1580 and 1360 cm(-1), which are ascribable to amorphous carbon, at a later stage of the observation, the intensities from the bright spot being more than 100 times stronger than those from the dim spot. The narrow bands are ascribed to a series of carbonaceous intermediates such as polyenes, graphite sheets with various sizes, and folded or reorganized forms of the sheets including carbon nanotubes and fullerenes, which are formed during the conversion of PDA to amorphous carbon. The random spectral fluctuation was interpreted by considering that the intermediates undergo thermally activated diffusion and get temporarily in contact with the SERS-active site, resulting in the enhancement of their Raman bands and the fluctuation.

Diacetylenes with Ionic‐Liquid‐Like Substituents: Associating a Polymerizing Cation with a Polymerizing Anion in a Single Precursor for the Synthesis of N‐Doped Carbon Materials

“…However,itisfavorable for polycyclization of the diyne units, the first and probably most important step of the carbonization process. This assumption has been verified experimentally by carrying out solid-state 13 CNMR studies on the pyrolysates of 1·Br and 2·Br prepared by thermolysis at 220 8C.…”

“…[19] These observations, along with the fact that virtually no weight loss was observed by TGA, allow one to conclude that polymerization occurs by polycyclization of the diacetylene units. In fact, detection in the solid-state 13 CNMR spectra of both pyrolysates of large signals centered at 130 ppm underneath the signals due to the imidazolium and benzimidazoliums ubstituents is consistent with the presence of polyaromatic structures. [19,22] The N1sX Ps pectrao ft he formed polymers should be the same as those of the precursors.…”

“…[26] We sought to gain insighti nto the structures of the polymeric networks formed at low temperature. To this end, we performed the thermolyseso f1·Br and 2·Br at 220 8Ca nd analyzed the pyrolysates by solid-state 13 CNMR spectroscopya nd XPS. We did not attemptt oa nalyze the residues by Raman spectroscopy,b ecause previous studies on similar samples revealed that the spectra only showed high fluorescence.…”

“…[19] We chose to analyze 1·Br and 2·Br because these precursorsa re simplerm odelst han the other four compounds,a nd also because previous studies have shown that these bromide salts did not polymerize topochemically when heated. [15,27] Figure 6 compares the 13 CNMR spectra of 1·Br and 2·Br recorded in solution with the solid-state NMR spectra obtained after pyrolysis at 220 8C. Clearly, thermal treatment results in the loss of the acetylenic signals at d % 70 ppm.…”

Analysis of Blinking SERS by a Power Law with an Exponential Function

“…However, there is a possibility that the blinking SERS is due to fluctuation of the enhanced EM field at the junction of an Ag nanoaggregate [15,35]. Moreover, SERS of amorphous carbon, which is formed by photoand thermo-degradation of the adsorbed molecules, shows similar behavior [47][48][49][50][51][52]. Thus, the mechanism of blinking SERS is still a contentious issue.…”