Photophysical properties of N-acetyl-menthyl anthranilate.

The results of a comprehensive investigation of the photophysical properties of the sunscreen analogue, N-acetyl menthyl anthranilate (NAMA), in various solvent systems are reported. Luminescence studies reveal that this compound is fluorescent (Phi(f)=0.16+/-0.01) in toluene and has a solvent dependent emission maximum in the range 363-370 nm. Phosphorescence has also been detected in low temperature glasses with an emission maximum at 420 nm in EPA, and a lifetime of 1.3 s; the triplet energy was found to be 311+/-3 kJ mol(-1). Kinetic UV-visible absorption measurements revealed a transient species with absorption maxima at 450 nm and solvent dependent lifetimes of 120-240 micros which are attributed to the triplet state. The triplet state is efficiently quenched by oxygen, leading to the formation of singlet oxygen in all of the solvent systems studied. The singlet oxygen quantum yields (Phi(Delta)), determined by time-resolved near-infrared luminescence measurements, were in the range 0.19-0.21.