Abstract

Rhenium tricarbonyl complexes are among the most important classes of coordination compounds in inorganic chemistry. Exploring their luminescent excited states, the lowest singlet (S-1) and lowest triplet (T-1), is an important topic to understand their interesting photophysical behavior and potential applications in organic light-emitting diodes (OLEDs). In this work, a systematic evaluation of the role of zero-field splitting (ZFS) and the geometric arrangement of different nitrogen-donor ligands, including pi-stacking interactions, in five selected rhenium luminescent complexes was performed. The optical properties have been deeply discussed using relativistic quantum mechanics methods and other theoretical approaches. Spin-orbit coupling TDDFT (SOC-TDDFT) calculations showed an excellent prediction of emission properties. The zero-field splitting (ZFS) values were relatively large, verifying the presence of the (MLCT)-M-3 state in the transition character of T1 and efficient spin-orbit coupling (SOC). The introduction of two nitrogen-donor ligands introduced pi-stacking interactions that produced a synergistic effect between the ligands and the metal center, promoting blueshift emissions and higher rate constants for T-1-S-0 transition mediated by SOC.