Theoretical treatment is given to the problem of a Coulomb center in thin wire with the dielectric constant æ≫1. The model describes adequately impurity centers and excitions in porous Si. The shape of Coulomb potential &fgr;(r) inside the wire disturbed drastically by image forces is analyzed. The exciton (or impurity) binding energy determined by the Schro¨dinger equation with &fgr;(r) demonstrates a manifold increase with the decrease of the wire radius.