An insight into fluorescent transition metal complexes.

Area of Science:

• Photochemistry
• Coordination Chemistry
• Materials Science

Background:

• Transition metal complexes usually emit from triplet excited states due to efficient intersystem crossing (ISC) facilitated by strong spin-orbit coupling (SOC).
• Singlet excited state emission is generally disfavored in these systems.
• Recent studies have identified transition metal complexes exhibiting high-intensity fluorescence, challenging the conventional understanding.

Purpose of the Study:

• To review and characterize fluorescent emission from transition metal complexes.
• To discuss the photophysical properties distinguishing fluorescent transition metal complexes.
• To explore related phenomena like delayed fluorescence and dual emissions.

Main Methods:

• Literature review of studies on fluorescent transition metal complexes.
• Analysis of photophysical characteristics: emission lifetimes, Stokes shift, and emission intensity under aerobic conditions.
• Categorization of different types of fluorescent emissions.

Main Results:

• Identified three key characteristics for fluorescent emission: nanosecond lifetimes, small Stokes shift, and intense emission under aerobic conditions.
• Singlet emission in many reviewed complexes originates from ligand-based fluorescence, indicating limited metal-ligand interaction.
• Reviewed delayed fluorescence and fluorescence-phosphorescence dual emissions as additional emission types.

Conclusions:

• Fluorescent emission from transition metal complexes, particularly ligand-based fluorescence, is feasible and exhibits distinct photophysical signatures.
• Understanding these characteristics is crucial for identifying and developing novel luminescent transition metal materials.
• Further investigation into delayed and dual emissions offers avenues for advanced photophysical applications.