Two-Photon Singlet Oxygen Sensitizers:  Quantifying, Modeling, and Optimizing the Two-Photon Absorption Cross Section

Several substituted difuranonaphthalenes have been identified as being viable sensitizers for the production of singlet molecular oxygen (a1Δg) upon two-photon nonlinear excitation with a focused laser beam. The two-photon absorption cross sections of these molecules are comparatively large and depend significantly on the functional groups attached to the chromophore. To facilitate the further development of such sensitizers, computational tools have been employed to model the two-photon absorption cross sections of some difuranonaphthalenes as well as distyryl benzenes that likewise can be viable singlet oxygen precursors. Ab initio calculations using response theory yield cross sections that reproduce experimental data well. Specifically, for these comparatively large molecules, the calculations not only model relative substituent-dependent changes well but also yield reasonably accurate cross sections. Thus, ab initio computational methods can indeed be used as a predictive tool in the design of potentially useful, two-photon singlet oxygen sensitizers.