Probing the effect of substituent groups in Ir(III) bis-tridentate complexes during deep-blue phosphorescent illuminating

Abstract

The emitting wavelength and efficiency of a series of blue phosphorescent bis-tridentate iridium complexes have been quantitatively evaluated using comprehensive theoretical approaches. By comparing the effect of different substituent groups in the tridentate ligands, their concrete influence to the radiative and non-radiative process have been analysed. The calculated wavelengths of phosphorescent molecules are in accordance with experimental results. The slightly blue shift in the phosphorescence of complex 1–4 is attributed to the ether link between two aromatic groups as compared to skyblue molecule. The method of calculating radiative decay constant (kr) and the non-radiative decay constant (knr) is verified and can predict the phosphorescent efficiency of iridium complexes in this study. The result shows that introducing ether link leads to the decrease of transition dipole moments, which consequently decreases kr. On the other hand, comparing with the strong electron attracting group CF3, kr and knr can both be enhanced by the electron donating group But. Further analysis of vibrational modes indicates that although spin-orbit coupling (SOC) is important to knr, while in this case, a higher reorganization energy at low frequency region determines a faster non-radiative decay process. At last, the inter-system crossing process (ISC) is considered. Unlike experimental speculation, a rate determining step is identified as from S1 to T1/T2/T3 in different complexes. The present study is expected to provide a theoretical method to evaluate the phosphorescent efficiency of bis-tridentate iridium complexes and investigate the influence of electron donating (attracting) substituent groups.