Switching-Off to Switching-On Triplet Formation Through Singlet-Triplet Intersystem Crossing in Porphyrin...

Area of Science:

• Materials Science
• Photochemistry
• Supramolecular Chemistry

Background:

• Solid-state artificial photosystems require precise control over singlet and triplet excited states for targeted photochemical reactions.
• Metal-organic frameworks (MOFs) provide a stable platform with large internal surface areas for exciton transfer.
• Porphyrins exhibit high intersystem crossing (ISC) efficiency, crucial for manipulating excited states.

Purpose of the Study:

• To investigate the influence of MOF framework assembly on excited state dynamics, specifically intersystem crossing (ISC) efficiency and triplet state lifetimes.
• To demonstrate control over the QY_ISC (quantum yield of ISC) and triplet behavior in MOF-based artificial photosystems.
• To establish design principles for creating artificial photosystems that selectively operate in either singlet or triplet manifolds.

Main Methods:

• Synthesis and characterization of free-base (FB) and palladium-metalated (Pd) porphyrin-based MOFs.
• Spectroscopic analysis to measure intersystem crossing (ISC) efficiency (QY_ISC) and triplet state lifetimes (τ_0.5).
• Comparison of excited state dynamics in MOFs versus their corresponding monomeric linkers.

Main Results:

• Framework assembly suppressed ISC in FB-MOFs but enhanced it in Pd-MOFs compared to monomers.
• MOF topology significantly influenced excited state dynamics, leading to short-lived triplets (τ_0.5 ≲10 ps) in microporous structures.
• Achieved extensive control over QY_ISC, ranging from 0 to nearly 100%.

Conclusions:

• MOF framework assembly offers a powerful strategy to modulate excited state dynamics, including ISC efficiency and triplet state persistence.
• The findings provide new design principles for developing artificial photosystems with tunable singlet or triplet state operation.
• This control is essential for advancing applications in photochemistry and energy conversion.