Deactivation Routes in Gold(I) Polypyridyl Complexes: Internal Conversion Vs Fast Intersystem Crossing

Area of Science:

• Photochemistry and Photophysics
• Organometallic Chemistry
• Coordination Chemistry

Background:

• Gold(I) complexes are investigated for their unique photophysical properties.
• Heterocyclic ligands, specifically pyridine derivatives, influence electronic and photophysical behavior.
• Understanding excited-state dynamics is crucial for applications in materials science and photoredox catalysis.

Purpose of the Study:

• To perform a detailed electronic spectral and photophysical characterization of three gold(I) complexes.
• To investigate the impact of varying numbers and arrangements of pyridine rings on photophysical properties.
• To correlate fast triplet state formation with charge transfer characteristics.

Main Methods:

• Electronic spectral analysis
• Photophysical measurements including quantum yields (fluorescence, internal conversion, triplet formation)
• Determination of rate constants for intersystem crossing (ISC) and internal conversion (IC)
• Evaluation of frontier orbital orthogonality to assess charge transfer (CT) character

Main Results:

• A correlation was observed between increased decay values of the singlet excited state (S₁) and enhanced charge transfer (CT) character of the lowest energy transition.
• Triplet state quantum yields ranged from approximately 50-70%.
• Intersystem crossing rate constants varied significantly, differing by nearly two orders of magnitude between complexes.

Conclusions:

• The study provides evidence for a correlation between intersystem crossing (ISC) and internal conversion (IC) mechanisms in these gold(I) complexes.
• The number and arrangement of pyridine rings in the heterocyclic chromophores directly impact the photophysical properties, particularly excited-state dynamics.
• Charge transfer character plays a significant role in facilitating fast triplet state formation.