A method of multiphoton photosensitizing a photoreactive composition
comprises irradiating the composition with light sufficient to cause
simultaneous absorption of at least two photons, thereby inducing at
least one acid- or radical-initiated chemical reaction where the
composition is exposed to the light. The composition comprises: (a) at
least one reactive species that is capable of undergoing such reaction;
and (b) at least one multi-component, multiphoton photoinitiator system.