NIR-Emissive Chromium(0), Molybdenum(0), and Tungsten(0) Complexes in the Solid State at Room Temperature

Area of Science:

• Inorganic Chemistry
• Materials Science
• Photophysics

Background:

• Developing near-infrared (NIR) emitters from earth-abundant elements is crucial for advanced optical applications.
• Existing NIR emitters often rely on precious metals or rare earth elements, limiting their widespread use.

Purpose of the Study:

• To synthesize and characterize novel chromium (Cr), molybdenum (Mo), and tungsten (W) carbonyl complexes.
• To investigate the photophysical properties, particularly dual visible (VIS) and NIR emission, of these complexes.
• To explore the potential of these complexes as NIR emitters in the NIR II region.

Main Methods:

• Synthesis of Cr(0), Mo(0), and W(0) carbonyl complexes featuring a pyridyl-mesoionic carbene (MIC) ligand.
• Detailed photophysical investigations, including time-resolved emission spectroscopy.
• Variable temperature step-scan Fourier-transform infrared (FTIR) spectroscopy.
• Density functional theory (DFT) calculations to support state assignments.

Main Results:

• All synthesized complexes exhibited dual emission in both the visible and NIR regions.
• Two distinct triplet excited states were identified as responsible for the observed emissions.
• The NIR emissive triplet state demonstrated exceptionally long lifetimes (up to 600±10 ns) and quantum yields (1.7 × 10⁻⁴) at room temperature.
• These represent the first Cr(0), Mo(0), and W(0) complexes emitting in the NIR II region.

Conclusions:

• The novel Cr, Mo, and W carbonyl complexes are efficient dual emitters with significant NIR emission properties.
• The long lifetimes and quantum yields of the NIR emissive states highlight their potential for applications requiring long-lived excited states.
• This work provides a new platform for developing earth-abundant NIR emitters, advancing the field of optoelectronics.