Time-Resolved Epr Study On The Photoexcited Triplet State Of The Electron-Donor-Acceptor Complex Formed In The System Of Fac-Tris[2-(4-Octyl-Phenyl) Pyridine] Iridium(Iii) And Tetracene

The physical properties of the phosphorescent organic light-emitting diode material fac-tris(phenylpyridine) iridium(III), Ir(ppy)(3), have been reported with experimental and theoretical studies. Here, the photochemical properties of the excited triplet state of partially modified fac-tris[2-(4-octyl-phenyl) pyridine] iridium(III), Ir(C(8)ppy)(3), were investigated using time-resolved electron paramagnetic resonance (tr-EPR) and optical methods by adding tetracene in the toluene solution. The tr-EPR observation at 77 K revealed the following two species: the excited triplet state of tetracene and another triplet species with zero field splitting parameters of vertical bar D vertical bar = 0.088 cm(-1) and vertical bar E vertical bar = 0.018 cm(-1) with characteristic spin polarization. The latter species was assigned to the electron donor acceptor (EDA) complex formed between Ir(C(8)ppy)(3) and tetracene. The mechanism of formation and the properties of this EDA complex, including the information on the principal axes of Ir-3(C(8)ppy)(3)*, are discussed.