Synthesis and electrochemical characterization of oligothiophenes with 1,2,4-triazine and 5,5′-bi-1,2,4-triazine as strong electron acceptor units

Two series of 1,2,4-triazine and 5,5′-bi-1,2,4-triazine-based oligothiophene derivatives have been developed and their molecular structures were confirmed by X-ray analysis. Electrochemical, spectroelectrochemical and spectral measurement were used to estimate their properties. The results show that the optical and electronic properties can be tuned over a broad range. The conjugation of two 1,2,4-triazine units leads to a significant strengthening of their electron-accepting properties in contrary to some widely used electron-acceptor units. The comparison of electrochemically estimated and DFT calculated electron affinity (EA) of oligothiophenes with 5,5′-bi-1,2,4-triazine and 1,2,4-triazine units indicates that conjugation of two triazine units leads to the formation of strong electron acceptor moiety with electrochemically estimated EA equal to 4 eV. Electron paramagnetic resonance spectra recorded during electrochemical reduction reveals the delocalization of radical mainly at 5,5′-bi-1,2,4-triazine core in contrary to 1,2,4‐triazine derivatives where thiophene arm is also involved. DFT calculations support the experimental results. These results indicate that obtained materials especially with 5,5′-bi-1,2,4-triazine units can be tested as n-type semiconductors for wide range of organic optoelectronic applications.