Investigation of Electronic Structures of Triplet States Using Step-Scan Time-Resolved Fourier-Transform...

Area of Science:

• Photophysics and Spectroscopy
• Materials Science
• Organic Chemistry

Background:

• Understanding excited-state dynamics in light-emitting materials is crucial for developing efficient optoelectronic devices.
• Triplet states play a significant role in the photophysical processes of many organic and organometallic compounds.

Purpose of the Study:

• To investigate triplet-triplet transitions in rose bengal and iridium complexes (Ir(ppy)3, Ir(piq)3, FIrpic).
• To assign observed absorption bands to specific triplet transitions and elucidate the nature of the triplet states.

Main Methods:

• Step-scan time-resolved Fourier-transform near-infrared spectroscopy.
• Excitation using a 355 nm laser.
• Theoretical calculations for spectral assignment.

Main Results:

• Rose bengal exhibited a transient absorption band at 9400 cm⁻¹ assigned to T₃ ← T₁.
• Iridium complexes showed intense bands at 7700-7500 cm⁻¹ assigned to higher triplet-triplet transitions (T₇ ← T₁ or T₆ ← T₁).
• The nature of the triplet states, including metal-to-ligand charge transfer (³MLCT), was determined for each material.

Conclusions:

• The study successfully characterized triplet-triplet transitions in diverse light-emitting materials.
• The findings provide valuable data for understanding and designing phosphorescent materials for applications.