Technical brief: Pump-probe paradigm in an integrating cavity to study photodecomposition processes

Area of Science:

• Photochemistry
• Spectroscopy
• Analytical Chemistry

Background:

• Assaying photodecomposition is experimentally challenging due to the need for simultaneous light exposure and spectral monitoring.
• Traditional spectrophotometers face limitations with turbid samples, uniform reactant exposure, and sensitivity for dilute solutions.

Purpose of the Study:

• To describe a novel system designed to overcome the challenges in assaying photodecomposition.
• To enable sensitive and practical monitoring of light-induced spectral changes in various samples.

Main Methods:

• A quartz integrating sphere was used with actinic light-emitting diodes (LEDs) and a rapid-scanning spectrophotometer (RSM).
• Actinic flashes were delivered during a dark period within the RSM scan cycle, creating a pump-probe setup.
• Absorbance was calculated considering the increased path length due to internal reflectance; retinoid photodecomposition was confirmed using high-performance liquid chromatography (HPLC).

Main Results:

• The system successfully monitored all-trans retinol photodecomposition upon exposure to 366 nm flashes, observing a decrease in absorbance and a blue shift in λmax.
• Singular value decomposition (SVD) analysis identified three spectral intermediates in the photodecomposition pathway.
• HPLC confirmed the overall retinol degradation.

Conclusions:

• The integrating sphere system enhances sensitivity and allows for the analysis of turbid samples.
• The pump-probe methodology enables precise interleafing of actinic exposure and spectral scanning.
• This system provides a foundation for future studies on retinoid degradation mechanisms and photoprotection by retinoid-binding proteins.