The luminescence spectra of the 8-methoxypsoralen excited-state complexes and photochemical product in argon, methanol/argon, and water/argon matrices at 10 K

The luminescence spectra of the 8-methoxypsoralen, 8-MOP, excited-state com plex have been observed in argon matrices at 10 K. The excited-state comple x is most probably an excimer, formed for cases in which high concentration s of 8-MOP are deposited in a pure-argon matrix. For cases in which 8-MOP i s in the presence of alcohol or water, another excited-state complex, an ex ciplex, is formed. Finally, when the 8-MOP/methanol/argon or 8-MOP/water/ar gon mixtures are photolyzed, a unique photochemical product is observed. Th is product is most probably the ground-state dimer, similar to the coumarin dimer formed in alcohol solutions upon UV irradiation. The luminescence em ission spectra of all three of the complexes are different and overlapping, resulting in spectra that seem anomalous. These results are similar to the reported anomalous emission spectrum of coumarin by Song, ct al., which is chemically and spectroscopically similar to 8-MOP.(1,2,3)