Metal-Centered Photoluminescence as a Tool for Detecting Phase Transitions in EuIII- and TbIII-Containing Metallomesogens
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- 作者：Sté ; phane Suá ; rez ; Daniel Imbert ; Fré ; dé ; ric Gumy ; Claude Piguet ; and Jean-Claude G. Bü ; nzli
- 刊名：Chemistry of Materials
- 出版年：2004
- 出版时间：August 24, 2004
- 年：2004
- 卷：16
- 期：17
- 页码：3257 - 3266
- 全文大小：231K
- 年卷期：v.16,no.17(August 24, 2004)
- ISSN：1520-5002
文摘
The non-mesogenic ligand L1, derived from a 1,7-diaza-18-crown ether, forms mesogeniccomplexes with EuIII and TbIII nitrates, Eu(NO3)3L1·0.25 H2O (EuL1) and Tb(NO3)3L1·1 THF(TbL1). Thermal analyses and polarized light microscopy data indicate the formation of aliquid-crystalline phase at 86 (Eu) and 81 
C (Tb), while isotropization occurs around 198-200 C, immediately followed by decomposition. In the case of EuIII, the mesogenic phase isunambiguously identified as being a hexagonal columnar mesophase by SAXD. Accordingto a detailed luminescence study, the crystalline form of EuL1 features two different metalion environments: (i) a C2-symmetrical site without coordinated water molecule (population: 79 ± 6%) and (ii) a low-symmetry site with one water molecule coordinated onto themetal ion (population: 21 ± 6%). For EuL1, the variation of both the relative intensity ofthe 5D0
7F2 transition, ln(IT/I295), and of the Eu(5D0) lifetime, ln(
T/295), over the Cr-Colhtransition have a S-shape dependence versus 1/T, allowing a precise determination of thetransition temperature. In the case of the luminescence intensity, corrections for the expecteddecrease versus increasing temperature (determined on a reference compound EuL2 withL2 devoid of mesogenic side chains) and for the refractive index change over the transitionstill leave a sigmoid dependence, pointing to a genuine effect generated by the phasetransition. Consequently, luminescence intensity and lifetime switching can be used to signalCr-LC transitions in Eu-containing mesogenic compounds. A similar effect is observed forTbL1, as far as the intensity of the 5D47F5 transition is concerned.
C (Tb), while isotropization occurs around 198-200 C, immediately followed by decomposition. In the case of EuIII, the mesogenic phase isunambiguously identified as being a hexagonal columnar mesophase by SAXD. Accordingto a detailed luminescence study, the crystalline form of EuL1 features two different metalion environments: (i) a C2-symmetrical site without coordinated water molecule (population: 79 ± 6%) and (ii) a low-symmetry site with one water molecule coordinated onto themetal ion (population: 21 ± 6%). For EuL1, the variation of both the relative intensity ofthe 5D07F2 transition, ln(IT/I295), and of the Eu(5D0) lifetime, ln(T/295), over the Cr-Colhtransition have a S-shape dependence versus 1/T, allowing a precise determination of thetransition temperature. In the case of the luminescence intensity, corrections for the expecteddecrease versus increasing temperature (determined on a reference compound EuL2 withL2 devoid of mesogenic side chains) and for the refractive index change over the transitionstill leave a sigmoid dependence, pointing to a genuine effect generated by the phasetransition. Consequently, luminescence intensity and lifetime switching can be used to signalCr-LC transitions in Eu-containing mesogenic compounds. A similar effect is observed forTbL1, as far as the intensity of the 5D47F5 transition is concerned.