Ultrafast spin crossover in 4-thiothymidine in an ionic liquid.

Area of Science:

• Photochemistry
• Chemical Physics
• Supramolecular Chemistry

Background:

• 4-thiothymidine is a modified nucleoside with potential applications in photodynamic therapy and as a photosensitizer.
• Ionic liquids offer unique solvation environments that can influence excited-state dynamics.
• Understanding excited-state pathways is crucial for designing light-activated molecules and processes.

Purpose of the Study:

• To investigate the excited-state dynamics of 4-thiothymidine.
• To elucidate the role of the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide in these dynamics.
• To determine the efficiency of intersystem crossing and triplet state formation.

Main Methods:

• Ultraviolet-Vis absorption spectroscopy.
• Time-resolved transient absorption spectroscopy.
• Computational modeling (if applicable, otherwise omit or generalize).

Main Results:

• The excited-state population of 4-thiothymidine branches upon UVA excitation.
• Efficient intersystem crossing to the triplet manifold occurs with a rate constant of 1.6 x 10^12 s^-1.
• A near-unity triplet yield is achieved after excitation at 340 or 360 nm.

Conclusions:

• Ionic liquids can promote efficient intersystem crossing in 4-thiothymidine.
• The study reveals a key photophysical pathway for 4-thiothymidine in a specific ionic liquid environment.
• These findings have implications for the development of novel photosensitizers and photochemistry in ionic liquid media.