Synthesis and Properties of New Tetrazines Substituted by Heteroatoms: Towards the World's Smallest Organic Fluorophores

New tetrazines substituted by heteroatoms have been synthesized and their electrochemical and photochemical properties investigated. All compounds are reversibly electroactive with standard potentials shifting cathodically according to the donor character of the substituent. The tetrazine derivatives are also fluorescent with maximum emission wavelengths in the range 550–575 nm. Some of them show very long fluorescence lifetimes (several tens of ns) and remain fluorescent in the solid state without major changes in the spectral features. The fluorescence of one of the derivatives can be efficiently quenched by the presence of electron‐rich compounds such as triphenylamines, phenol or anisole, which make them very promising compounds for sensor applications. Promising molecules for sensor applications have been obtained with novel tetrazine derivatives. The compounds display a fully reversible electrochemical behavior and an intense fluorescence, both in solution and in the solid state. The fluorescence lifetimes are long (several tens of ns) and the emission can be efficiently quenched by electron donors like aromatic compounds (see figure).