Studies of magnetically induced circular polarization phosphorescence in Pt-rich pi-conjugated polymers at high fields*

We have measured magnetic-field induced circular polarization (FICPO) phosphorescence in various Pt-rich pi-conjugated polymers, in which the spin-orbit coupling can be tuned by changing the intrachain Pt atom concentration through incorporation of different organic ligand spacers. FICPO response, which includes the difference between right ($\sigma +)$ and left ($\sigma $-) circularly polarized phosphorescence emission bands, increases linearly at low field $B$\textless 5 T, but starts to saturate at $B$\textasciitilde 17 T. We determined the effective g-factor from the Zeeman splitted $\sigma +$ and $\sigma $- emission bands, and found that its deviation from the free electron value (g$=$2) scales with the strength of spin-orbit coupling in the Pt-polymer chains. Surprisingly, we also found that at intermediate $B \quad \sigma +$ emission intensity at the higher photon energy is stronger than that of the $\sigma $- emission, indicating $B$-dependent radiative decay rates in the triplet spin sublevels.