Prototropically Controlled Dynamics of Cytosine Photodecay

Area of Science:

• Computational chemistry
• Photochemistry
• Spectroscopy

Background:

• Cytosine exists in various prototropic tautomeric forms.
• Understanding tautomer-specific properties is crucial for molecular behavior.

Purpose of the Study:

• Investigate the influence of cytosine tautomers on UV/vis spectra.
• Analyze excited state decay dynamics of different cytosine tautomers.
• Correlate computational findings with experimental observations.

Main Methods:

• Mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT).
• Nonadiabatic molecular dynamics (NAMD) simulations.
• UV/vis spectral simulations.

Main Results:

• Simulated spectra suggest the presence of the H3N keto-amino cytosine tautomer under experimental conditions.
• NAMD simulations reveal a wide range of excited state decay constants (0.1–1.3 ps) for different tautomers.
• The H1N tautomer exhibits slow decay due to a barrier on its excited state energy surface.

Conclusions:

• The H3N tautomer may be present and contribute to experimental observations.
• Photodecay dynamics likely result from a combination of simultaneously present cytosine tautomers.
• The presence of tautomers significantly affects cytosine's spectral and decay properties.