Excited-state dynamics of sinapate esters in aqueous solution and polyvinyl alcohol film

Sunscreens are widely applied to protect skin from solar ultraviolet irradiation. The photodynamics of a series of sinapate esters are explored by the femtosecond transient absorption spectroscopy combined with the time-dependent density functional theory. The ester group is determined to have a negligible effect on the bright V (pi pi*) state, evidenced by the nearly same steady-state absorption and emission spectra of these sinapate esters. The nonradiative trans-cis photoisomerization along the V(pi pi*) state is found to be non-linearly dependent with the ester group size. The smallest methyl sinapate and the largest sinapoyl dimethyl malate have the shortest excited-state lifetimes (ca. 7 ps). In the poly(vinyl alcohol) (PVA) film, the constrained environment leads to the emissions blue shifted and excited-state lifetime prolonged to more than one hundred picoseconds. The photostabilities of these sinapate esters are also tested and as high as the plant sunscreen sinapoyl malate.