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Transparent Ion-Exchange Membrane Exhibiting Intense Emission under a Specific pH Condition Based on Polypyridyl Ruthenium(II) Complex with Two Imidazophenanthroline Groups
| Content Provider | MDPI |
|---|---|
| Author | Kamebuchi, Hajime Tamaki, Satoshi Okazawa, Atsushi Kojima, Norimichi |
| Copyright Year | 2021 |
| Description | The development and the photophysical behavior of a transparent ion-exchange membrane based on a pH-sensitive polypyridyl ruthenium(II) complex, [(bpy)_{2}Ru^{II}(H_{2}bpib)Ru^{II}$(bpy)_{2}](ClO_{4})_{4}$ (bpy = 2,2′-bipyridine, $H_{2}$bpib = 1,4-bis([1,10]phenanthroline[5,6-d]-imidazol-2-yl)benzene), are experimentally and theoretically reported. The emission spectra of [(bpy)_{2}Ru^{II}(H_{2}bpib)Ru^{II}$(bpy)_{2}$]@Nafion film were observed between pH 2 and pH 11 and showed the highest relative emission intensity at pH 5 (λ_{max}$^{em}$ = 594.4 nm). The relative emission intensity of the film significantly decreased down to 75% at pH 2 and 11 compared to that of pH 5. The quantum yields (Φ) and lifetimes (τ) showed similar correlations with respect to pH, Φ = 0.13 and τ = 1237 ns at pH 5, and Φ = 0.087 and τ = 1014 ns and Φ = 0.069 and τ = 954 ns at pH 2 and pH 11, respectively. These photophysical data are overall considerably superior to those of the solution, with the radiative- $(k_{r}$) and non-radiative rate constants $(k_{nr}$) at pH 5 estimated to be $k_{r}$ = 1.06 × $10^{5}$ $s^{−1}$ and $k_{nr}$ = 7.03 × $10^{5}$ $s^{−1}$. Density functional theory calculations suggested the contribution of ligand-to-ligand- and intraligand charge transfer to the imidazolium moiety in $Ru-H_{3}$bpib species, implying that the positive charge on the $H_{3}$bpib ligand works as a quencher. The Ru-Hbpib species seems to enhance non-radiative deactivation by reducing the energy of the upper-lying metal-centered excited state. These would be responsible for the pH-dependent “off-on-off” emission behavior. |
| Starting Page | 400 |
| e-ISSN | 20770375 |
| DOI | 10.3390/membranes11060400 |
| Journal | Membranes |
| Issue Number | 6 |
| Volume Number | 11 |
| Language | English |
| Publisher | MDPI |
| Publisher Date | 2021-05-27 |
| Access Restriction | Open |
| Subject Keyword | Membranes Inorganic Chemistry Transparent Emitter Polypyridyl Ruthenium(ii) Complex Nafion Membrane |
| Content Type | Text |
| Resource Type | Article |
