Platinum 2,2′:6′,2′-terpyridine complexes as probes for CMC determination of sodium dodecyl sulfate solutions

The platinum complex [Pt(terpy) (OH)]+(terpy = 2,2′:6′,2′-terpyridine) is a molecular "light switch" for the determination of critical micelle concentration (CMC) in sodium dodecyl sulfate (SDS) micellar system in aqueous solution. No emission from [Pt(terpy) (OH)]+is observed when the complex is dissolved in water or in very dilute SDS solution but a strong luminescence with emission maximum at 605 nm and excited-state lifetime of 0.1 μs is observed once the SDS concentration reaches the CMC. The emission wavelength of the hydrophobic platinum complex [Pt(mpterpy) (OH2)]2+(mpterpy = 4′-(p-methoxyphenyl)-2,2′:6′,2′-terpyridine) is also a sensitive parameter for CMC determination. Unlike [Pt(terpy) (OH)]+, [Pt(mpterpy ) (OH2)]2+has an emission at 720 nm in SDS solution with concentration below CMC. When the concentration of SDS reaches the CMC, there is a sudden, large hypochromic shift of the emission maximum from 720 nm to 610 nm. The emission maximum of [Pt(mpterpy) (OH2)]2+stays at 610 nm as the SDS concentration increases further beyond the critical micelle concentration.