Donor-acceptor-donor tetrazines containing a ferrocene unit: synthesis, electrochemical and spectroscopic properties.

Donor-acceptor-donor tetrazines containing ferrocene moieties and phenyl unit as a pi-bridge have been synthesized and characterized. UV-vis spectroscopic and cyclic voltamperometric results indicate sizable intramolecular charge transfer interactions in the ground state when the ferrocene is directly bound to the tetrazine. On the other hand, the results show reduction of the electron-donor strength of ferrocene moieties when there is a phenyl linkage. Both tetrazines display a high reduction potential. The role of ferrocenyl groups appear to be detrimental to maximize the cubic hyperpolarizability gamma of tetrazines, as compared to purely organic groups such as thiophene. A possible explanation for this behavior may originate from metal-to-ligand charge transfer processes.