Mesomorphic structures of protonated surfactant-encapsulated polyoxometalate complexes.
Keggin-type heteropolyanions, H(3)PW(12)O(40) (HPW), Na(3)PW(12)O(40) (NaPW), H(4)SiW(12)O(40) (HSiW) and K(4)SiW(12)O(40) (KSiW), were encapsulated by a cationic surfactant, di[12-(4'-octyloxy-4-azophenyl)dodecyloxy]dimethylam monium bromide (L), through the replacement of counterions. The resulting surfactant-encapsulated polyoxometalate complexes were characterized by UV-vis, Raman, and NMR spectra in detail. The measurement results indicated that some azobenzene groups of the surfactant were protonated in the complexes HL/HPW (HL is the abbreviation of the protonated surfactant), HL/NaPW, and HL/HSiW during the process of encapsulation, whereas the protonation was not observed in L/KSiW. The thermotropic liquid crystal properties of these complexes were investigated by differential scanning calorimetry, polarized optical microscopy and variable-temperature X-ray diffraction. Interestingly, different smectic mesophases were observed between the protonated HL/HSiW and the non-protonated L/KSiW, which suggests that the protonation of azobenzene groups in HL/HSiW plays a key role in the liquid crystalline organization. However, protonated HL/HPW and HL/NaPW exhibit a similar smectic B phase to that of the de-protonated one, L/HPW. A competitive balance between the phase separation and the volume minimization of surfactants was proposed to explain the self-organized liquid crystal structures of these protonated and non-protonated complexes. To the best of our knowledge, the present investigation provides a specific example for protonated hybrid materials with stable liquid crystal properties.
Yin
Shengyan
S
State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012, People's Republic of China.
Li
Wen
W
Wang
Jinfeng
J
Wu
Lixin
L
D001391:Azo Compounds / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D008024:Ligands; D050866:Liquid Crystals / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D044367:Phase Transition; D011522:Protons; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D017973:Tungsten Compounds / Q000737:chemistry*
D001391:Azo Compounds; D008024:Ligands; D009942:Organometallic Compounds; D011522:Protons; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; D017973:Tungsten Compounds; C529654:bis(12-(4'-octyloxy-4-azophenyl)dodecyloxy)dimethylammonium; C009850:azobenzene