Two-photon photosensitized production of singlet oxygen

Singlet molecular oxygen (a(1)Delta (g)) has been produced and optically de tected upon two-photon nonlinear excitation of a sensitizer with a focused laser beam. The experiments were performed using toluene solutions with eit her a substituted difuranonaphthalene or a substituted distyryl benzene as the sensitizer. The data indicate that the two-photon absorption cross sect ions of the difuranonaphthalenes are comparatively large and depend signifi cantly on the functional groups attached to the chromophore. The time-resol ved 1270 nm phosphorescence signals used to characterize the production of singlet oxygen are limited in much the same way as signals from other two-p hoton spectroscopic studies (e.g., weak signals that can be masked by scatt ered radiation). Nevertheless, the two-photon singlet oxygen signals also r eflect the unique advantages of this nonlinear optical technique (e.g., dep th penetration in the sample afforded by irradiation in a spectral region v oid of the more dominant one-photon linear transitions and spatial resoluti on afforded by irradiation with a focused laser beam).