The present invention provides a method for cleavage of labile functional groups from molecules by the action of electromagnetic radiation, wherein the molecules are contacted with a chemical compound whose triplet state is energetically higher than the triplet state of the labile functional group, and are subsequently exposed to electromagnetic radiation. Further, the invention provides a method for preparing DNA chips by spatially addressed, light-controlled nucleotide synthesis on solid substrates, said method comprising the following steps: a) reacting the unprotected terminal 3' or 5' hydroxy group of a nucleoside and/or of a nucleotide arranged on the solid substrate under usual conditions with a photolabile protective group and optionally purifying the reaction product, b) applying a solution, suspension or dispersion of a chemical compound, whose triplet state is energetically higher than the triplet state of the photolabile protective group, to the surface of the carrier, said surface comprising the nucleotides and/or nucleosides modified in step a): c) irradiating, in a spatially selective manner, the surface of the carrier treated in step b) with electromagnetic radiation in the UV/VIS range with simultaneous, spatially selective release of a reactive OH group and subsequently reacting it with a nucleoside and/or nucleotide comprising a 5' or 3'OH group, said nucleoside and/or nucleotide being further provided with a photolabile functional group. Moreover, the present invention provides a chemical composition comprising a molecule having a labile functional group, as well as a chemical compound whose triplet state is higher than the triplet state of the labile functional group, and it describes the use of the chemical composition for preparing DNA chips.