A luminescent pH sensor based on a sol-gel film functionalized with a luminescent organometallic complex

A rhenium(I) tricarbonyl complex with a 3-(pyridin-2-yl)pyrazole chromophoric ligand and a functionalized organosilane spectator ligand, [Re(py-pzH)(CO)₃(L₁)](CF₃SO₃) (1) [where py-pzH=3-(pyridin-2-yl)pyrazole, L(I)=3-N-(pyridin-4-ylmethylene)aminopropyltriethoxysilane], as well as its analog, [Re(py-pzH)(CO)₃(py)](CF₃SO₃) (2) (where py=pyridine) have been synthesized. The room temperature MLCT luminescence properties of 1 and 2 (λ(max) at 484 and 489 nm, respectively) were found to be sensitive to the protonation-deprotonation status of the 3-(pyridin-2-yl)pyrazole ligand. Spectrofluorometric pH titration of 2 in aqueous media revealed an excited state pK(a) of 7.05. Sol-gel material formed from hydrolysis of 1 was successfully spin-coated onto glass microscope slides. The result was a sol-gel based luminescent pH sensor capable of responding over a wide pH range from pH 2.3 to 12 in air. The applicability of the principle of direct perturbation of electronic factors of sensor molecules in the development of luminescent chemical sensing materials is demonstrated.