Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5404251 | Journal of Luminescence | 2007 | 9 Pages |
Abstract
The photophysical properties of bis((4-(phenylethynyl)phenyl)ethynyl)bis(tributylphosphine) platinum(II) with 2,2-bis(methylol)propionic acid (bis-MPA) dendritic substituents were studied. The fluorescence emission decay upon excitation in the UV (typically 350-380 nm) was rapid, in the order of 1 ns or shorter. In oxygen-saturated tetrahydrofuran solvent, the phosphorescence decay time was in the order of 200 ns. Bright phosphorescence at 530 nm was found for dendrimers under certain conditions. The associated phosphorescence decay time considerably increased to above 100-200 μs at higher concentrations (30-100 μM), and in oxygen-evacuated samples. Thus, it was clarified that the strongest triplet quenching was caused by oxygen dissolved in the sample, since it was possible to reversibly go between the bright and quenched phosphorescent state by freeze-thaw pumping cycles. The bright phosphorescence formed spontaneously for the cases with the larger dendritic substituents is implying a chromophore protecting effect. From time-dependent density functional calculations, the electronic structure of a few low-lying singlet and triplet states are discussed. A new mechanism for efficient triplet state formation and phosphorescence of Pt-ethynyls is proposed. Here, a fast relaxation via internal conversion takes the excited population of the dominant ÏâÏ* excitation into a lower singlet state of ligand-to-metal charge transfer character of ÏÏ* type. This allows an efficient inter system crossing to the triplet state manifold.
Related Topics
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Chemistry
Physical and Theoretical Chemistry
Authors
Mikael Lindgren, Boris Minaev, Eirik Glimsdal, Robert Vestberg, Robert Westlund, Eva Malmström,