Exotically knotted 2-spheres and the fundamental groups of their complements

We show that for any finitely presented group G G , there is a simply connected closed 4-manifold containing an infinite family of topologically isotopic but smoothly inequivalent 2-links whose 2-link group is G G . We also show that, if G G satisfies the necessary topological conditions, these 2-links have nullhomotopic components.