Abstract
A heteroditopic ligand H-2-L consisting of a dihydroxybenzene (catechol)-unit linked via an amide bond to a pyridyl-unit and its methyl-protected precursor Me-2-L were synthesized, characterized, and their photophysical properties investigated. The three accessible protonation states of the ligand, H-3-L+, H-2-L, and H-L-, showed distinct H-1 NMR, absorption and emission spectroscopic characteristics that allow pH-sensing. The spectroscopic signatures obtained act as a guide to understand the signaling mechanism of the luminescent pH and molybdate sensor [Re-(bpy)(CO)(3)(H-2-L)](+). It was found that upon deprotonation of the 2-hydroxy group of H-2-L, a ligand-based absorption band emerges that overlaps with the Re(d pi)-> bpy metal-to-ligand charge transfer (MLCT) band of the sensor, reducing the quantum yield for emission on excitation in the 370 nm region. In addition, deprotonation of the catechol-unit leads to quenching of the emission from the Re(d pi)-> bpy (MLCT)-M-3 state, consistent with photoinduced electron transfer from the electron-rich, deprotonated catecholate to the Re-based luminophore. Finally, reaction of 2 equiv of [Re(bpy)(CO)(3)(H-2-L)](+) with molybdate was shown to give the zwitterionic Mo(VI) complex [MoO2{Re(CO)(3)-(bpy)(L)}(2)], as confirmed by electrospray ionization (ESI) mass spectrometry and X-ray crystallography. The crystal structure determination revealed that two fully deprotonated sensor molecules are bound via their oxygen-donors to a cis-dioxo-MoO2 center.
Original language | English |
---|---|
Pages (from-to) | 1105-1115 |
Number of pages | 11 |
Journal | Inorganic Chemistry |
Volume | 50 |
Issue number | 3 |
DOIs | |
Publication status | Published - 7 Feb 2011 |
Keywords
- STATE PROTON-TRANSFER
- BIS(CATECHOLAMIDE) SIDEROPHORE ANALOG
- EXCITED-STATE
- BRIDGING LIGAND
- CIS-DIOXOMOLYBDENUM(VI) COMPLEX
- INFRARED-SPECTROSCOPY
- DIIMINE COMPLEXES
- SULFITE OXIDASE
- BINDING-SITES
- CATECHOL