Room temperature phosphorescence characteristics of platinum(II) chelates with 8-quinolinol derivatives in aqueous micellar solutions

Abstract

Phosphorescence from platinum(II) chelates of 8-quinolinol (8-Q), 5-sulfo-8-quinolinol (SQ), and 5-sulfo-7-iodo-8-quinolinol (SIQ) at ca. 630 nm is strongly enhanced in certain kinds of surfactant micellar solutions in the presence of sulfite ion as a chemical de-oxygenator. Among these ligand systems the [Pt(II)(SIQ) 2] 2− chelate is most highly phosphorescent with a quantum yield of 0.028 in n-dodecyl-β- d-maltoside (DOM) micelles at 298 K because of the heavy-atom effect of iodine. The emission due to the dianionic 1 : 2 chelates of SQ and SIQ are strongly facilitated either in cationic and non-ionic surfactant micelles such as hexadecyltrimethylammonium chloride (CTAC) or bromide (CTAB), Brij-35, Triton X-100, and DOM in sharp contrast to the slight sensitization by sodium dodecylsulfate (SDS) micelles of similar charge. Anionic SDS micelles do not work well even for the uncharged [Pt(II)(8-Q) 2] chelate. The emission decay lifetimes of the chelates in de-oxygenated micellar solutions are in a similar range of 28 μs with CTAB to 37 μs with DOM, at 298 K. In a pre-micellar region of CTAC, below the critical micelle concentration, the chelate is also luminescent as the ion-pair of (CTA) 2[Pt(II)(SIQ) 2]. The highly sensitive phosphorescence detection of Pt(II) ion is achievable using the SIQ–DOM–sulfite system, giving a 3 σ detection limit of 30 nM or 6 ng Pt ml −1