The influence of charge transfer on the emissive properties of pyridine dipyrrolide bismuth complexes

Abstract

We report on the emissive properties of four new pyridine dipyrrolide bismuth complexes Bi(^R1PDP^R2)Br, modified with electron-donating (–OMe) or electron-withdrawing (–CF₃) substituents at the ligand. These complexes exhibit red phosphorescence at cryogenic temperatures with emission wavelengths ranging from 602 to 642 nm as a response to the electronic character of the substituents R₁ and R₂. A profound similarity between the pairs Bi(^CF3PDP^CF3)Br and Bi(^CF3PDP^OMe)Br, and Bi(^OMePDP^CF3)Br and Bi(^OMePDP^OMe)Br is attributed to improved conjugation between the respective phenyl ring and the PDP core, as based on TD-DFT calculations and crystallographic studies. The larger quantum yield of Bi(^CF3PDP^CF3)Br is attributed to the enhancement of the ³LMCT character of the electronic transition through the introduction of the electron-withdrawing –CF₃ substituents.