Cleavage occurs by irradiation with near-UV light (300-350 nm). Try using a Black Ray XX-15 UV lamp (Ultraviolet Products Inc., San Gabriel, CA) at a distance of 15 cm (emission peak 365 nm, 300 nm cut-off, 1.1 mW intensity at~31 cm).
Most modified oligos can be stored and resuspended just as unmodified oligos, with the exception of photocleavable or photolabile modifications such as Bromo-dU, PC Spacer, PC Biotin, and PC Linker. These should be kept away from light
References
Bai, X., Zengmin, L., Jockusch, S., Turro, N.J., Ju, J. Photocleavage of a 2-nitrobenzyl linker bridging a fluorophore to the 5’-end of DNA. Proc. Natl. Acad. Sci. USA (2003), 100: 409-413. - PC Spacer (photocleavable)