期刊
JOURNAL OF ORGANIC CHEMISTRY
卷 79, 期 4, 页码 1611-1619出版社
AMER CHEMICAL SOC
DOI: 10.1021/jo402516n
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资金
- NSF IGERT: Materials Creation Training Program (MCTP) [DEG-0654431]
- National Science Foundation [CHE-1048804]
- [DMR1101934]
- Direct For Mathematical & Physical Scien [1266405, 1101934] Funding Source: National Science Foundation
- Division Of Chemistry [1266405] Funding Source: National Science Foundation
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1048804] Funding Source: National Science Foundation
- Division Of Materials Research [1101934] Funding Source: National Science Foundation
We describe the synthesis, characterization, photochemical isomerization, and rotational dynamics of a crystalline molecular gyroscope containing an azobenzene bridge (trans-2) that spans from one end of the stator to other, with the intention of exploring its function as a molecular brake. While single crystal X-ray diffraction analysis of a photochemically inactive dichloromethane solvate was used to confirm the molecular and packing structures of trans-2, a nanocrystalline pseudopolymorph was shown to be photoactive, and it was analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy, and variable temperature solid state H-2 NMR before and after photoisomerization. It was shown that the nanocrystalline suspension irradiated with lambda = 340 nm reaches a photostationary state with 34% of cis-isomer, as compared to that observed in solution where the corresponding value is 74%. Line shape analysis of solid state H-2 NMR spectra of a phenylene-d(4) isotopologue, obtained as a function of temperature, indicated that rotation in crystals of the trans-2 isomer, with a mean activation energy of 4.6 +/- 0.6 kcal/mol and a pre-exponential factor exp(29.4 +/- 1.7), is ten times faster than that of samples containing the cis-2 isomer, which has a higher mean activation energy of 5.1 +/- 0.6 kcal/mol and a lower pre-exponential factor of exp(27.9 +/- 1.3).
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