Tricyclic cytosine (tC) is a fluorescent analog of cytosine designed for RNA imaging within live cells, facilitating the study of RNA synthesis, degradation, and trafficking with single-cell precision through confocal imaging. This compound features excitation/emission maxima (λ) of 375/505 nm, an extinction coefficient of 4000 M^-1cm^-1, and a quantum yield of 0.2.