For three indolylfulgides the quantum efficiency of the ring-opening reaction upon pre-excitation is investigated in a multipulse experiment. The quantum efficiency grows by factor of up to 3.4, when the pre-excitation pulse immediately precedes the excitation process. The change in quantum efficiency after pre-excitation is discussed as a function of reaction time, steady-state quantum efficiency and energetic barriers in the excited electronic state. The observed differences can be explained by the molecular properties of the investigated indolylfulgides. (C) 2010 Elsevier B.V. All rights reserved.