This invention relates to the field of nucleic acid chemistry, more specifically to the field of compositions of matter that comprise triphosphates of modified 2′-deoxynucleosides and oligonucleotides that are formed when these are appended to the 3′-end of a primer, wherein said modifications comprise NH2 moiety attached to their 3′-hydroxyl group and a fluorescent species in a form of a tag affixed to the nucleobase via a linker that can be cleaved. Such compositions and their associated processes enable and improve the sequencing of oligonucleotides using a strategy of cyclic reversible termination, as outlined in U.S. Pat. No. 6,664,079. Most specifically, the invention concerns compositions of matter that are 5′-triphosphates of ribo- and 2′-deoxyribonucleosides carrying detectable tags and oligonucleotides that might be derived from them. The invention also concerns processes wherein a DNA polymerase, RNA polymerase, or reverse transcriptase synthesizes said oligonucleotides via addition of said triphosphates to a primer.