A fluorescent nitrogenous base and nucleosides including the fluorescent nitrogenous base are provided. Nucleosides including the fluorescent nitrogenous base are capable of Watson-Crick base pairing with naturally occurring nucleosides. The nucleosides including the fluorescent nitrogenous base have many uses including but not limited to use in probes, in the synthesis of nucleic acids, and in investigating nucleic acid interactions with other nucleic acids and/or with proteins.