BIPHOTONIC CHEMISTRY OF PHENANTHRENE UNDER 308 nm EXCIMER LASER IRRADIATION

Abstract— –The high intensity laser induced photochemistry of phenanthrene is complex and appears to be non-linear with respect to laser intensity. Photochemical products primarily involve the solvent (CH₂C1₂) and phenanthrene coupling. These species exhibit strong absorption and emission which are red-shifted from that of phenanthrene. In the presence of a-methyl styrene, styrene oligomers are formed, but no dimers, indicating that there are no a-methyl styrene cation radical reactions. In all cases of laser irradiation the solutions become acidic, which is ascribed to the deprotonation of the phenanthrene cation radical. Acid formation does not occur in the presence of a-methyl styrene under CW irradiation with a conventional Xe lamp. These differences are ascribed to photoionization from the singlet state for laser irradiation while under CW conditions triplet-triplet annihilation can produce the phenanthrene cation radical.