Theoretical Study of the Phosphorescence Spectrum of Tris(2-phenylpyridine)iridium Using the Displaced Harmonic Oscillator Model

Abstract

We present a comprehensive investigation of the phosphorescence spectrum of Ir(ppy)3 (ppy=2-phenylpyridine), which is greatly influenced by vibration of the complex. General formalism of the emission spectrum is derived using a thermal vibration correlation function formalism for the transition between two adiabatic electronic states in polyatomic molecules. Displacements and Duschinsky rotation of potential energy surfaces are included within the framework of a multidimensional harmonic oscillator model. This formalism gives a reliable description of the emission spectrum of Ir(ppy)3. The calculated results indicated that the 0→1 transition between the T1 state and the S0 state makes a large contribution to the emission spectrum, especially the vibrational modes below 1600 cm–1. The breathing vibration of the ligands and the CC and CN stretching vibrations of benzene and pyridine rings are the main reasons for the appearance of the shoulder peak in the spectrum. The Boltzmann distribution makes the intensities of both the main and the shoulder peaks decrease, and the peaks are close together. When coupled with first-principles density functional theory (DFT) calculations, the present approach appears to be an effective tool to obtain a quantitative description and detailed understanding of the spectra and photophysical processes of polyatomic molecules.