It has been verified that the photochemical degradation of hematoporph
yrin free base (HpFB) in ''lipid-like'' solutions in THF proceeds acco
rding to a two-photon mechanism and the fluorescent product of the rea
ction is of chlorin type with lambda(Q(OO))(em) = 650 nm. The excitati
on occurred at 560+/-20 nm.