[Cr(ddpd)2](3+): A Molecular, Water-Soluble, Highly NIR-Emissive Ruby Analogue.

Area of Science:

• Inorganic Chemistry
• Photochemistry
• Materials Science

Background:

• Achieving bright, long-lived emission from first-row transition-metal complexes is a significant challenge.
• Tuning energy levels is crucial for controlling photophysical properties.

Purpose of the Study:

• To develop a novel strategy for enhancing luminescence in transition-metal complexes.
• To synthesize and characterize a chromium(III) complex with exceptional photophysical properties.

Main Methods:

• Rational design of a tridentate ligand (ddpd) with a large bite angle and strong σ-donating ability.
• Synthesis of the chromium(III) complex [Cr(ddpd)2](3+).
• Spectroscopic and photophysical characterization, including quantum yield and lifetime measurements.

Main Results:

• The ligand-field splitting in [Cr(ddpd)2](3+) shifts the deactivating (4)T2 state above the emitting (2)E state.
• Prevention of back-intersystem crossing leads to high near-infrared phosphorescence quantum yields and lifetimes.
• The resulting complex, [Cr(ddpd)2](BF4)3, exhibits high water solubility and stability.

Conclusions:

• A new strategy for achieving bright, long-lived emission from first-row transition metals has been demonstrated.
• The developed chromium(III) complex is suitable for robust oxygen sensing in the near-infrared region.