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 complex have been observed in argon matrices at 10 K. The excited-state complex is most probably an excimer, formed for cases in which high concentrations of 8-MOP are deposited in a pure-argon matrix. For cases in which 8-MOP is in the presence of alcohol or water, another excited-state complex, an exciplex, is formed. Finally, when the 8-MOP/methanol/argon or 8-MOP/water/argon mixtures are photolyzed, a unique photochemical product is observed. This product is most probably the ground-state dimer, similar to the coumarin dimer formed in alcohol solutions upon UV irradiation. The luminescence emission 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, et al., which is chemically and spectroscopically similar to 8-MOP. 1,2,3