The present invention relates to compositions useful as probes and in other applications and methods of their use. In some embodiments, nucleotides are prepared and functionalized with dyes. In some embodiments a first molecule is functionalized with an alkynyl group, a second molecule is functionalized with an azide group, and said first and second molecules are mixed under conditions to form a conjugate with a 1,2,3-triazol group. In further embodiments, a nucleotide is functionalized with an alkynyl group, a dye is functionalized with an azide group, and mixing the nucleotide and the dye forms a conjugate capable of emitting light.