CF® dye with methyltetrazine reacts with cyclooctene (TCO, methylcyclopropene) containing molecules via copper free click chemistry. This copper free bioorthogonal reaction is useful for labeling live cells, or when there are concerns about native protein function loss with copper in cell extracts. Methyltetrazine has improved chemical stability compared to tetrazine. CF®500-Methyltetrazine has excitation/emission at 500/510 nm, and is designed for intracellular copper-free reaction with azide.