Energy Upconversion Using Platinum(II)-BPI Photosensitizers.

Area of Science:

• Organometallic Chemistry
• Photochemistry
• Materials Science

Background:

• Platinum(II) complexes are investigated for their photophysical properties and potential applications in catalysis and optoelectronics.
• Heteroleptic complexes offer tunable electronic and steric properties through judicious choice of ligands.
• Bis(2-pyridylimino)isoindoline ligands provide a robust scaffold for coordinating metal centers.

Purpose of the Study:

• To synthesize and characterize novel heteroleptic platinum(II) complexes with a diethyl-substituted bis(2-pyridylimino)isoindoline (BPIEt) core and varying alkynyl coligands.
• To investigate the structural, redox, photophysical, and photochemical properties of these complexes.
• To evaluate their potential as photosensitizers for triplet-triplet annihilation upconversion (TTA-UC).

Main Methods:

• Synthesis of five Pt(II) complexes with different alkynyl coligands.
• Full characterization using NMR, IR, UV-vis, luminescence, transient absorption spectroscopies, HRMS, and cyclic voltammetry.
• X-ray crystallography for structural determination.
• Density Functional Theory (DFT) calculations.
• Triplet-triplet annihilation upconversion (TTA-UC) experiments.

Main Results:

• Structural analysis revealed a deviation from ideal square planar geometry.
• Redox potentials indicated a Pt(II/III) oxidation and ligand-based reductions.
• Complexes exhibited phosphorescence in toluene (λem = 625-644 nm) with strong metal-to-ligand charge transfer (MLCT) character.
• Efficient singlet oxygen generation (up to 73%) was observed.
• Maximum TTA-UC efficiency of 29.6% was achieved for Pt(BPIEt)(4).

Conclusions:

• The synthesized Pt(II) complexes are structurally characterized and possess tunable photophysical properties.
• They are efficient photosensitizers for singlet oxygen generation and TTA-UC.
• The BPIEt ligand scaffold is suitable for developing advanced platinum-based photofunctional materials.