Zinc(II) Monomeric, Dimeric, and Trimeric Photosensitizers with Microsecond-Lived Intra-ligand Charge Transfer...

Area of Science:

• Photochemistry and Photophysics
• Coordination Chemistry
• Materials Science

Background:

• Zinc(II) photosensitizers are less explored than copper(I) complexes due to higher energy charge transfer states.
• Understanding excited-state dynamics is crucial for developing efficient photosensitizers.

Purpose of the Study:

• To investigate the excited-state dynamics of three Zn(II)-phenanthroline complexes (monomer, bimetallic helicate, trimetallic helicate).
• To correlate structural differences with photophysical properties and photoredox capabilities.

Main Methods:

• Time-resolved X-ray absorption (tr-XAS) spectroscopy.
• Femto- and nanosecond optical transient absorption (OTA) spectroscopy.
• Density Functional Theory (DFT) calculations.

Main Results:

• Ultrafast formation of singlet intraligand charge transfer (¹ILCT) states within femtoseconds.
• Generation of microsecond-lived triplet intraligand charge transfer (³ILCT) states via intersystem crossing (ISC).
• Structural variations (monomer vs. helicates) impact ISC rates and excited-state lifetimes, attributed to ligand interactions and strain.

Conclusions:

• Zn(II) complexes can exhibit efficient excited-state dynamics, forming long-lived triplet states.
• Noncovalent interactions and ligand strain significantly influence photophysical properties.
• The studied complexes show potential for applications in photoredox catalysis.