Triplet state relaxation processes of the OLED emitter Pt(4,6-dFppy)(acac)

The emitting triplet state of Pt(4,6-dFppy)(acac) doped into n-octane is studied at cryogenic temperatures by site-selective high-resolution optical spectroscopy. The investigations reveal a very specific zero-field splitting (ZFS) pattern of the emitting T1 state and the individual deactivation times of the substates to the singlet ground state S0. Spin-lattice relaxation (SLR) processes occurring between the T1 substates are ascribed to a combination of the direct and the Raman process. Due to the relatively long SLR time at low temperature, a Boltzmann distribution is not established directly after the excitation pulse below ≈2 K.