Highly efficient red phosphorescent organic light-emitting devices with facially encumbered and bulky Pt(Ⅱ) porphyrins

摘要

We report effective enhancement of external quantum efficiency of phosphorescent organic light-emitting devices (OLEDs) with facially encumbered and bulky meso-aryl substituted Pt(Ⅱ) porphyrins, probably suppressing non-radiative deactivation. The peak external quantum efficiencies (QEs) of the phosphorescent OLEDs with facially non-encumbered Pt(Ⅱ) porphyrin 1, facially encumbered Pt(Ⅱ) porphyrin 2, Pt(Ⅱ) porphyrin 3 that bears bulkier 3,5-di-tert-butylphenyl substituents, and "doubly-decamethylene-strapped" Pt(Ⅱ) porphyrin 4 were 1, 4.2, 7.3, and 8.2 %, respectively. The trend increasing performance in the order of 1 < 2 < 3 < 4 is related to facial encumbrance and steric bulkiness of Pt(Ⅱ) porphyrins. Furthermore, in the case of Pt(Ⅱ) porphyrin 4, it is considered that the "double straps" severely restrict rotational freedom of the meso-aryl substituents. The lifetimes for Pt(Ⅱ) porphyrins 1-4 at a current density of 0.55 mA/cm~2 were 80, 103, 140, and 152 μs, respectively. The trend that the triplet lifetime becomes longer in the order of 1 < 2 < 3, 4 suggests that facial encumbrance and steric bulkiness suppress non-radiative deactivation. The triplet lifetimes of Pt(Ⅱ) porphyrins 1-4 were all gradually shortened with increasing current densities, suggesting possible triplet-triplet annihilation and/or triplet-charge carrier recombination.