The photochemical modifications induced by excimer 248 nm ablation of PMMA films doped with organic compounds exemplifying different photoreactivities are presented. The employed dopants were naphthalene and the photosensitive bromo- and iodonaphthalene. The comparison of the three systems shows that ablation with nanosecond (30 ns) pulses results in significant modifications of the photosensitive halonaphthalene dopants, including an increase in their photolysis yields and the formation of additional products. In sharp contrast, in the ablation with 500 fs pulses, photochemical modifications are found to be limited.