Optimal control theory is used to design laser pulses that enhance the trans-cis photoisomerization of retinal, which is modeled by coupled potential curves to examine coupling effects on control mechanisms. Based on numerical results, a new type of pump-dump control pathway, in which an optimal pulse achieves high target probability without directly modifying a potential coupling, is proposed. The key feature of this control is that a shaped wave packet passes a curve-crossing point adiabatically in the ground electronic state. (C) 2003 Elsevier Science B.V. All rights reserved.