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Switchable Green and White Luminescence in Terbium‐Based Ionic Liquid Crystals
Author(s) -
Getsis Anna,
Mudring AnjaVerena
Publication year - 2011
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201100168
Subject(s) - chemistry , luminescence , differential scanning calorimetry , acetonitrile , mesophase , terbium , ionic liquid , crystallography , liquid crystal , phase (matter) , ion , organic chemistry , materials science , physics , optoelectronics , thermodynamics , catalysis
[C 12 mim]Br (C 12 mim = 1‐dodecyl‐3‐methyl) and [C 12 mpyr]Br (C 12 mpyr = N ‐dodecyl‐ N ‐methylpyrrolidinium), both doped with TbBr 3 , as well as the neat compounds [C 12 mim] 3 [TbBr 6 ] and [C 12 mpyr] 3 [TbBr 6 ] show mesomorphic behavior and are able to form smectic liquid crystalline phases. The thermal phase behavior of all compounds was investigated by hot‐stage polarizing optical microscopy and differential scanning calorimetry. Whilst the doped compounds crystallize around room temperature, the neat compounds solidify as glasses around –5 °C and qualify also as ionic liquids. The crystal structure of the acetonitrile solvate of the imidazolium compound, [C 12 mim] 3 [TbBr 6 ] · 2CH 3 CN, could be determined by single X‐ray diffraction. The structure features alternating double layers of [C 12 mim] + cations and [TbBr 6 ] 3– octahedra with hydrogen bonded acetonitrile. [C 12 mim] 3 [TbBr 6 ] · 2CH 3 CN can serve as a structure model for the smectic mesophase of the solvate‐free [C 12 mim] 3 [TbBr 6 ]. All materials show strong green luminescence from the 5 D 4 ‐level of Tb 3+ after excitation into the 4f 8 → 4f 7 5d 1 transition. In case of the imidazolium compounds, the color of this emission can be switched between green and blue‐white depending on the excitation energy. After excitation with λ ex = 254 nm, strong green emission mainly from the 5 D 4 ‐level of Tb 3+ is observed. With λ ex = 366 nm, only the blue‐white luminescence from the imidazolium cation itself is detected.