Solid-state NMR study on dynamics of p-nitroaniline molecules in FSM-type mesoporous silicas at high loading levels
✍ Scribed by Yoshihiko Komori; Shigenobu Hayashi
- Publisher
- Elsevier Science
- Year
- 2006
- Tongue
- English
- Weight
- 271 KB
- Volume
- 91
- Category
- Article
- ISSN
- 1387-1811
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✦ Synopsis
We have investigated dynamics of deuterated p-nitroaniline (pNA-d) molecules in FSM-16 mesoporous silica (FSM) and FSM modified with trimethylethoxysilane (C1FSM) with different loading amounts ranging from 10 to 50 mass% by means of solid-state NMR. We have measured temperature dependence of 2 H NMR spectra and spin-lattice relaxation times (T 1 ) as well as 13 C magicangle-spinning (MAS) NMR spectra. The 2 H and 13 C MAS NMR spectra indicate that there are two modes of motions; an isotropic motion and a fast wobbling one. The rates of the wobbling motion are estimated from the 2 H T 1 results. pNA-d molecules in the FSM/pNA-d sample of 10 mass% undergo the wobbling motion at the low temperatures, whereas the isotropic motion is relatively suppressed at the high temperatures. In the samples of 20 and 30 mass% the wobbling motion is suppressed at the low temperatures, whereas the isotropic motion is enhanced at the high temperatures. The above changes further proceed in the sample of 50 mass%. The temperature dependences of 2 H spectra in C1FSM/pNA-d of 13 and 20 mass% are similar to those of FSM/pNA-d of 20 and 30 mass%. C1FSM/pNA-d of 30 mass% shows spectra intermediate between FSM/pNA-d of 30 mass% and FSM/pNA-d of 50 mass%. We have proposed ''three-layer model'' to explain the above NMR results.