Cyanine5.5 tetrazine is a far-infrared luminescent dye. Cyanine5.5 tetrazine is a Cyanine5.5 derivative contains a tetrazine moiety. Cyanine5.5 tetrazine can be used for in vivo imaging and low background applications. Cyanine5.5 tetrazine is a click chemistry reagent, it contains a Tetrazine group that can undergo an inverse electron demand Diels-Alder reaction (iEDDA) with molecules containing TCO groups.