Picosecond Dynamics of Avobenzone in Solution

Area of Science:

• Photochemistry
• Chemical Dynamics
• Spectroscopy

Background:

• Avobenzone, a common sunscreen ingredient, undergoes photoisomerization upon UV exposure.
• This process forms non-chelated enol (NCE) isomers, some of which decrease sunscreen efficacy.
• Previous studies on nanosecond- to microsecond-scales could not characterize unstable NCE isomers.

Purpose of the Study:

• To investigate the picosecond dynamics of avobenzone photoisomerization.
• To directly observe and characterize unstable non-chelated enol isomers.
• To determine the lifetimes and branching ratios of these transient species.

Main Methods:

• Excitation of avobenzone at 350 nm.
• Time-resolved spectroscopy using broadband visible and 266 nm probe pulses.
• Analysis of isomer formation and relaxation dynamics on the picosecond timescale.

Main Results:

• Direct spectroscopic evidence for two unstable NCE isomers of avobenzone.
• Determination of the lifetimes for these newly observed NCE isomers.
• Quantification of the branching ratio between the observed NCE isomer pathways.

Conclusions:

• The picosecond timescale reveals previously unobserved NCE isomers of avobenzone.
• Understanding these unstable isomers is critical for optimizing sunscreen photostability.
• This study provides fundamental insights into avobenzone's photochemical behavior.