Tunable phosphorescent NIR oxygen indicators based on mixed benzo- and naphthoporphyrin complexes

Area of Science:

• Materials Science
• Photochemistry
• Coordination Chemistry

Background:

• Porphyrin complexes are vital in photochemistry and sensing.
• Developing novel metalloporphyrins with tailored photophysical properties is crucial for advanced applications.
• Near-infrared (NIR) emission is desirable for biological and optical sensing due to reduced tissue autofluorescence and deeper penetration.

Purpose of the Study:

• To synthesize and characterize novel π-extended phosphorescent palladium(II) and platinum(II) porphyrin complexes.
• To investigate the photophysical properties, including absorption, emission, quantum yields, and luminescence lifetimes.
• To explore the potential of these complexes as NIR-absorbing oxygen indicators with tunable properties.

Main Methods:

• Synthesis of π-extended phosphorescent palladium(II) and platinum(II) porphyrin complexes with fused benzene rings.
• Photophysical characterization including UV-Vis absorption and emission spectroscopy.
• Determination of phosphorescence quantum yields and luminescence decay times in deoxygenated toluene solutions.
• Density Functional Theory (DFT) calculations to elucidate complex geometries and electronic structures.

Main Results:

• Synthesized palladium(II) and platinum(II) porphyrins with fused naphtho and benzodibenzotribenzo groups exhibit intensive NIR absorption (628-691 nm) and emission (815-882 nm).
• Platinum(II) porphyrins show high phosphorescence quantum yields (25-53%) and short lifetimes (21-44 μs).
• Palladium(II) porphyrins display lower quantum yields (7-18%) but longer lifetimes (106-206 μs).
• DFT calculations confirm nonplanar geometries and support the observed absorption characteristics.

Conclusions:

• The π-extension of porphyrin systems effectively tunes photophysical properties into the NIR region.
• These novel metalloporphyrins function as effective NIR-absorbing oxygen indicators.
• The synthesized complexes offer tunable luminescence and oxygen sensitivity, paving the way for advanced sensor development.