Norrish photolytic cleavage

At the bench recently, I had cause to develop new conditions for a desulfurisation reaction – with some precedent to suggest that the process could be induced by light. It would turn out to be a very tricky problem indeed. The molecule contained not only the necessary structural components for the intended photoreaction, but also a host of ketones. I feared these might be susceptible to unwanted photo-excitation and cleavage, following a mechanism elucidated by British physical chemist Ronald Norrish. How would I achieve selectivity for my intended reaction?