Tuning the optical and electrochemical properties of core-substituted naphthalenediimides with styryl imide substituent

The effect of styryl imide substitution on optical and electrochemical properties of core-substituted naphthalenediimides was examined by synthesizing a series of naphthalenediimide molecules. 2-Ethylhexylamino and 5-(2-ethylhexyl)thiophene groups were used as core substituents. The optical and electrochemical properties of styryl imide substituted compounds were compared with other imide substitutions including hydrogen, 2-ethylhexyl, and 4-thienylphenyl. Generally, the imide substituents had little effect on the optical properties, except when the combination of alkylamino core and styryl imide substituents was used. In this latter case, we observed a 104 nm red-shift of the absorption onset upon film formation, resulting in an unusually broad visible absorption (500-800 nm) for these types of molecules. This is explained by the planarity of the molecule and the formation of intermolecular aromatic donor-acceptor type interactions. These results show that imide substituents play a role in tuning opto-electronic properties of NDI molecules, and that NDI molecules with styryl imide substituents merit further evaluation for opto-electronic applications.