u v or visible light by irradiation with light sources such as fluorescent lamps mercury vapor lamps or photographic flash bulbs additionally activation will occur by heating e g 95 u00b0 c for 10 min or by incubation with salts of transition metals e g at 37 u00b0 c for 60 min photoactivation is the preferred method unreacted components are removed by solvent extraction the compound of formula 13 is then contacted with reagents specific for the removal of group y under appropriate conditions to generate the compound of formula 14 str20 wherein r 1 to r 4 and e are as described above reagents and conditions for the removal of the particular protecting groups are generally well known the compound having the structure shown in formula 14 is then contacted with a thiol reactive form of a label or ligand so as to form a labeled nucleic acid probe having the structure shown in formula 15 str21 wherein r 1 to r 4 and e are as described above r 9 is the thiolated conjugate of the thiol reactive group in the thiol reactive label and l is a detectable label or ligand suitable labels or ligands include but are not limited to enzymes such as peroxidase or alkaline phosphatase enzyme cofactors enzyme inhibitors sugars radioisotopes chemiluminescent compounds chromophores fluorophores scintillants avidin or streptavidin binding molecules and the like suitable thiol reactive groups include maleimides iodoacetamides pyridyl disulfides vinyl pyridines vinyl sulfones acrylates aryl mercurial compounds and aziridino compounds covalently linked.