Examining solvent effects on the ultrafast dynamics of catechol

Area of Science:

• Photochemistry
• Physical Chemistry
• Spectroscopy

Background:

• Catechol is a key building block of eumelanin.
• Understanding catechol's excited state dynamics in polar solvents is crucial for its biological and material applications.
• Previous studies proposed different conformations and aggregation states for catechol in solution.

Purpose of the Study:

• To investigate the effect of a polar, hydrogen bond accepting solvent (acetonitrile) on catechol's excited state decay.
• To determine the influence of catechol aggregation on its excited state lifetime.
• To validate the use of explicit-solvent ab initio methods for predicting vibrational frequencies in interacting solvents.

Main Methods:

• Fourier transform infrared (FTIR) spectroscopy.
• Explicit-solvent ab initio frequency prediction.
• Ultrafast transient absorption spectroscopy.
• Steady-state spectroscopy.

Main Results:

• At 5 mM in acetonitrile, catechol exists as nonaggregated monomers in a "closed" conformation.
• The excited state (S₁) lifetime of nonaggregated catechol is 713 ps.
• At 75 mM in acetonitrile, catechol aggregation increases the S₁ lifetime to 1700 ps, attributed to altered excited-state landscapes.

Conclusions:

• Explicit-solvent methodology is essential for accurate vibrational frequency calculations in strongly interacting solvents.
• Catechol aggregation significantly impacts its excited state dynamics in polar solvents.
• Combining spectroscopic techniques with computational methods provides deep insights into catechol's behavior as a monomer and aggregate.