Vibrational Dynamics in Dendridic Oligoarylamines by Raman Spectroscopy and Incoherent Inelastic Neutron Scattering
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- 作者：Irena Kulszewicz-Bajer ; Guy Louarn ; David Djurado ; Lukasz Skorka ; Marek Szymanski ; Jean Yves Mevellec ; Stephane Rols ; Adam Pron
- 刊名：Journal of Physical Chemistry B
- 出版年：2014
- 出版时间：May 15, 2014
- 年：2014
- 卷：118
- 期：19
- 页码：5278-5288
- 全文大小：544K
- 年卷期：v.118,no.19(May 15, 2014)
- ISSN：1520-5207
文摘
Vibrational dynamics in triarylamine dendrimers was studied in a complementary way by Raman and infrared (IR) spectroscopies and incoherent inelastic neutron scattering (IINS). Three molecules were investigated, namely, unsubstituted triarylamine dendrimer of the first generation and two dendrimers of the first and second generation, substituted in the crown with butyl groups. To facilitate the assignment of the observed IR and Raman modes as well as the IINS peaks, vibrational models, based on the general valence force field method (GVFF), were calculated for all three compounds studied. A perfect consistency between the calculated and experimental results was found. Moreover, an important complementarity of the vibrational spectroscopies and IINS was established for the investigated dendrimers. The IINS peaks originating mainly from the C鈥揌 motions were not restricted by particular selection rules and only dependent on the IINS cross section. To the contrary, Raman and IR bands were imposed by the selection rules and the local geometry of the dendrimers yielding mainly C鈥揅 and C鈥揘 deformation modes with those of C鈥揌 nature of much lower intensity. Raman spectroscopy was also applied to the studies of the oxidation of dendrimers to their cationic forms. A strong Raman resonance effect was observed, since the spectra of the studied compounds, registered at different levels of their oxidation, strongly depended on the position of the excitation line with respect to their electronic spectrum. In particular, the blue (458 nm) excitation line turned out to be insensitive toward the cationic forms yielding very limited spectral information. To the contrary, the use of the red (647 nm) and infrared (1064 nm) excitation lines allowed for an unambiguous monitoring of the spectral changes in dendrimers oxidized to nominally monocationic and tricationic states. The analysis of oxidation-induced spectral changes in the tricationic state indicated that the charge storage configuration predominantly involved one spinless dication of the quinoid bond sequence and one radical cation. However, small numbers of dications were also found in a nominally monocationic state, where only radical cations should have been present. This finding was indicative of some inhomogeneity of the oxidation.