Photophysics of Ruthenium(II) Complexes with Thiazole π-Extended Dipyridophenazine Ligands

Area of Science:

• Photochemistry
• Coordination Chemistry
• Materials Science

Background:

• Transition-metal complexes are key for visible-light-driven charge-transfer.
• Ruthenium(II) polypyridyl complexes offer tunable photophysical properties.

Purpose of the Study:

• Synthesize and characterize novel ruthenium(II) complexes (Ru1, Ru2) with dipyridophenazine ligands linked to 4-hydroxythiazoles.
• Investigate the excited-state dynamics and emission properties of these complexes.

Main Methods:

• Synthesis of ruthenium(II) polypyridyl complexes.
• Femtosecond-to-nanosecond transient absorption spectroscopy.
• Nanosecond emission spectroscopy.
• Time-dependent density functional theory (TD-DFT) calculations.

Main Results:

• Photoexcitation populates both metal-to-ligand charge-transfer (MLCT) and intraligand charge-transfer (ILCT) states.
• Two distinct excited-state branches observed: a short-lived 3MLCT state (150-400 ps) and a long-lived 3ILCT state (40-300 ns).
• Ruthenium(II) complexes display long-lived dual emission attributed to both 3ILCT and 3MLCT states.

Conclusions:

• The synthesized ruthenium(II) complexes exhibit complex excited-state dynamics with dual emission.
• The interplay between MLCT and ILCT states is crucial for long-lived charge-transfer states.
• These findings contribute to the design of novel photoactive materials.