Efficient structural modification of electron‐withdrawing substituents on Pt(II) complexes for red emitters: A theoretical study

Abstract

In this study, the electronic structures and optical properties of a cyclometalated Pt(II) complex (M1) and a series of derivatives (M1–F, M1–CF3, and M1–CN) with electron‐withdrawing substituents (–F, –CF3, and –CN) at the carbazole moiety were theoretically investigated by density functional theory and time‐dependent density functional theory. The calculation results reveal that these Pt complexes display deep red phosphorescence emission above Λ = 640 nm. When the 3MLCT/π → π* to triplet metal‐centered 3MC/d–d state decay mechanism is taken into consideration, the nonradiative decay rate constant (knr) decreased in the order M1 > M1–CF3 > M1–F > M1–CN. The <T1|HSOC|Sm> and kr values of M1‐F are similar with those of M1, however the Knr rate ofM1‐F is larger than that of M1. M1–F is expected to have improved quantum yields. Moreover, through the analyses of the HOMO/LUMO level and triplet energy, it is found that the introduction of –F and –CN substituents in M1 results in efficient energy transfer from the host material 4,4′‐N,N′‐dicarbazole‐biphenyl to these complexes. In view of the electroluminescent applications in organic light‐emitting diodes, M1–F can serve as efficient deep‐red guest materials with improved electron injection and transport ability.