Characterisation of the lowest singlet and triplet excited states of S-flurbiprofen

Abstract

The photophysical properties of S-flurbiprofen [S-2-fluoro-α-methyl-4-biphenylacetic acid], a nonsteroidal anti-inflammatory drug, have been examined using steady-state and time-resolved spectroscopic techniques. The energy of its first singlet excited state is 99 kcal mol⁻¹. The fluorescence quantum yields and lifetimes (at 300 nm) have been determined in acetonitrile, methanol, hexane and PBS; they are in the range 0.15 < ϕ_F <  0.33 and 0.7 < τ_F < 2.0 ns. The intersystem crossing quantum yields are between 0.45 and 0.71; the λ_max of the T–T absorption is 360 nm, and the triplets live from 15 to 106 µs. Steady state photolysis in aqueous medium leads to S-2-hydroxy-α-methyl-4-biphenylacetic acid via photonucleophilic aromatic substitution, in addition to the photodecarboxylation products observed in organic solvents.