Fig. 3
Photochemical properties of ara-5I and ara-5A. a Molecular orbitals for T1 states (3ππCS* and 3ππring*) of ara-5I. b Calculated potential energy profile of ara-5A T1 3ππCS* state C–S bond homolysis furnishing triplet sulfur atom and singlet C8-carbene tautomer of ara-4A. Blue line = T1-state energy, black line = ground-state energy. The minimum-energy path along the C–S distance (Å) was obtained by calculation at the ADC(2)/cc-pVTZ level of theory. c Calculated ara-5I triplet excited state T1 topography. Parabolas fitted to calculated T1 minima energies and optimised T2/T1 minimum-energy state crossing, which represents the transition state between these minima. d Calculated ara-5A triplet excited state T1 topography. No ring-puckered minimum was found on the T1 hypersurface due to the higher 3ππring* state energy. e–f FTAS recorded between λ = 340 and 530 nm with λ = 290 nm excitation (pump) pulses. e FTAS of ara-5I recorded between λ = 340 and 530 nm with λ = 290 nm excitation (pump) pulses. Inset: Calculated excited state absorption spectra for the two possible configurations of ara-5I. f FTAS of ara-5A recorded between λ = 340 and 530 nm with λ = 290 nm excitation (pump) pulses. Inset: Calculated excited state absorption spectra for the singlet and triplet states of ara-5A
