title: Luminescence color tuning of Pt(II) complexes and a kinetic study of trimer formation in the photoexcited state.
abstract: We investigated the luminescence properties and color tuning of [Pt(dpb)Cl] (dpbH=1,3-di(2-pyridyl)benzene) and its analogues. An almost blue emission was obtained for the complex [Pt(Fmdpb)CN] (FmdpbH=4-fluoro-1,3-di(4-methyl-2-pyridyl)benzene), modified by the introduction of F and CH3 groups to the dpb ligand and the substitution of Cl by CN. As the concentration of the solution was increased, the color of the emission varied from blue to white to orange. The color change resulted from a monomer-excimer equilibrium in the excited state. A broad emission spectrum around 620 nm was clearly detected along with a structured monomer emission around 500 nm. Upon further increases in concentration, another broad peak appeared in the longer wavelength region of the spectrum. We assigned the near-infrared band to the emission from an excited trimer generated by the reaction of the excimer with the ground-state monomer. The emission lifetimes of the monomer, dimer, and trimer were evaluated as τM =12.8 μs, τD =2.13 μs, and τT =0.68 μs, respectively, which were sufficiently long to allow association with another Pt(II) complex and dissociation into a lower order aggregate. Based on equilibrium constants determined from a kinetic study, the formation of the excimer and the excited trimer were concluded to be exothermic processes, with ΔG*D =-24.5 kJ mol(-1) and ΔG*T =-20.4 kJ mol(-1) respectively, at 300 K.
authors.affiliation: Department of Materials System Science, Graduate School of Nanobiosystem Sciences, Yokohama City University, 22-2 Seto, Yokohama, 236-0027 (Japan), Fax: (+81) 45-787-2413.
authors.forename: T
authors.initials: T
authors.lastname: Kayano
authors.forename: S
authors.initials: S
authors.lastname: Takayasu
authors.forename: K
authors.initials: K
authors.lastname: Sato
authors.forename: K
authors.initials: K
authors.lastname: Shinozaki
keywords: aggregation; kinetics; luminescence; metal-metal interactions; platinum complexes