New halogenated phenylbacteriochlorins and their efficiency in singlet-oxygen sensitization

Halogenated phenylbacteriochlorins are synthesized with high yields in a two-step procedure. They have strong absorbances in the red and are very stable to air and light at room temperature. Flash photolysis measurements show that the triplet states of these bacteriochlorins have 30 mus lifetimes in deaerated toluene, that are quenched with diffusion-controlled rate constants by molecular oxygen. Time-resolved photoacoustic measurements, with nanosecond and nanocalorie resolution, show that these bacteriochlorins sensitize the formation of singlet oxygen with nearly unity quantum yield. However, singlet-oxygen phosphorescence measurements indicate that physical quenching occurs before the singlet-oxygen molecules diffuse into solution, and nearly half of the sensitized singlet states are lost.