The present invention relates to a process for synthesizing biopolymers by stepwise assembly from protected synthesis building blocks which carry two-stage protective groups. The two-stage protective groups are activated by a first illumination step and eliminated by a subsequent chemical treatment step. Photoactivatable components which considerably speed up the activation process via intramolecular triplet sensitizers or/and have fluorescence properties are used. The two-stage protective groups can be used in particular within the framework of quality control.