Vibrational Control of Spin-Orbit Coupling Enhances Triplet-Triplet Annihilation Upconversion Efficiency

Area of Science:

• Photochemistry and photophysics
• Quantum chemistry
• Materials science

Background:

• Singlet-triplet intersystem crossing (ISC) is crucial for photovoltaics, photocatalysis, and photochemistry.
• Traditionally, ISC is explained by spin-orbit coupling (SOC) as an electronic interaction.
• Vibronic SOC, where nuclear dynamics modulate SOC, is increasingly recognized but experimentally challenging to control.

Purpose of the Study:

• To experimentally demonstrate that vibrational excitation can enhance SOC and accelerate ISC.
• To establish a mechanistic link between nuclear motion and spin dynamics.
• To explore novel methods for controlling ISC in photochemical systems.

Main Methods:

• Utilized a BODIPY sensitizer within a triplet-triplet annihilation upconversion system.
• Employed selective mid-infrared excitation of skeletal vibrational modes.
• Applied time-resolved mid-infrared spectroscopy and density functional theory (DFT) calculations.

Main Results:

• Selective vibrational excitation significantly increased upconversion emission by 156%.
• This enhancement was directly attributed to the accelerated ISC rate.
• Vibrational strengthening of SOC was confirmed through spectroscopic and computational analyses.

Conclusions:

• Nuclear dynamics, specifically skeletal vibrations, can effectively enhance SOC and ISC.
• This work provides the first direct experimental evidence for vibrationally mediated SOC control.
• The findings open new avenues for designing materials with tailored spin dynamics for advanced photochemical applications.