Unravelling the mechanism of water sensing by the Mg2+ dihydroxy-terephthalate MOF (AEMOF-1 ‘)

In this contribution we build upon our previous work on the MOF [Mg(H(2)dhtp)(H2O)(2)]center dot DMAc (AEMOF-1 center dot DMAc) and its activated dry version AEMOF-1 ‘ which has been shown to exhibit excellent luminescence sensing properties towards water in organic solvents. We demonstrate through combined structural and photophysical studies that the observed changes in the fluorescence properties of AEMOF-1 ‘ upon hydration arise from a structural transformation to the mononuclear complex [Mg(H(2)dhtp)(H2O)(5)]center dot H2O (H(4)dhtp = 2,5-dihydroxyterepthalic acid) (1). In the latter complex, excited state intramolecular proton transfer (ESIPT) is strongly favoured thereby leading to enhanced and red shifted emission in comparison to AEMOF-1 center dot DMAc. Powder X-ray diffraction measurements confirmed that complex 1 is identical to the hydrated form of AEMOF-1 center dot DMAc. As in the case of AEMOF-1 ‘, the dry form of complex 1 (1 ‘) is also an effective sensor for the determination of traces of water in tetrahydrofuran (THF). This work demonstrates that the same chromophore may exhibit very different emission properties when it exists in different chemical environments and that these transformations may be controlled and utilized in water sensing applications

Luminescent Properties of the Hexakis(Nitrito)Europate(Iii) Ion [Eu(No 2 ) 6 ] 3−

International audienceThe 12-coordinated hexakis(nitrato)europate(III) ion displays a luminescence spectrum compatible with Th, symmetry, with essentially a single emission line at 16 873 cm−1 arising from the 5D0→7F1 transition. At low temperature (4.2 - 170 K), the lifetime of the 5D0 level amounts to 10.9 ms and then sharply decreases because of vibrational de-excitation processes (Ea = 2 250 ± 1 490 cm−1). The forbidden 5D0→7F0 transition displays an extensive pattern of Stokes and anti Stokes vibrational components and its energy reflects a nephelauxetic parameter for the nitrite ions δO(NO2) equal to -14.4, slightly larger than the one associated to the nitrate ion in [Eu(NO3)6]3-. The ligand excitation spectrum contains several bands displaying extensive vibrational structure mostly due to the δ(NO2) vibrational mode

Luminescent Properties of Lanthanide Nitrato Complexes with Substituted Bis(benzimidazolyl)pyridines.

International audienceThe quantum yields of the europium-centered and ligand-centered luminescence of 1:1 and 1:3 complexes with bis(benzimidazolyl)pyridines is rationalized by taking into account several electronic and structural factors. Photophysical properties in solution and in the solid state as well as structural data are also reported