Photon upconversion sensitized by a Ru(II)-pyrenyl chromophore

Area of Science:

• Photochemistry
• Materials Science
• Spectroscopy

Background:

• Ruthenium chromophores are known for their long-lived triplet states, useful in energy transfer processes.
• Photon upconversion allows for the generation of higher energy photons from lower energy light.
• Anthracene exhibits fluorescence, a property that can be modulated by external stimuli.

Purpose of the Study:

• To investigate the photon upconversion of anthracene sensitized by a ruthenium complex.
• To explore the mechanism of anti-Stokes singlet fluorescence generation.
• To determine the efficiency and power dependence of the upconversion process.

Main Methods:

• Utilized a ruthenium complex, [Ru(5-pyrenyl-1,10-phenanthroline)(3)](PF(6))(2), as a sensitizer.
• Employed low-intensity non-coherent green light for selective excitation of the sensitizer.
• Confirmed the mechanism using transient absorption spectroscopy and photoluminescence experiments.

Main Results:

• Achieved anti-Stokes singlet fluorescence of anthracene at low incident power densities (<500 μW cm⁻²).
• Demonstrated that photon upconversion proceeds via sensitized triplet-triplet annihilation (TTA) of anthracene.
• Identified distinct power regimes (quadratic-to-linear) for the upconversion process under 488 nm excitation.

Conclusions:

• The ruthenium sensitizer effectively facilitates TTA in anthracene for photon upconversion.
• The observed anti-Stokes fluorescence is a direct consequence of the sensitized TTA mechanism.
• This system shows potential for applications requiring efficient light harvesting and energy conversion.