Flavoenzymes are an important class of redox-active enzymes that are responsible for maintaining a
range of cellular processes [1]. For example, they have been shown to play a significant role in the
dehydrogenation, hydroxylation and oxidation of a range of biological substrates and one and
two-electron transfer reactions both to and from other redox centers [2]. In the majority of systems, the
main flavin co-factor present is either flavin adenine dinucleotide (FAD) or flavin mononucleotide
(FMN), which is usually non-covalently bound to the active site of the enzyme through an array of
specific non-covalent interactions. In addition to providing a scaffold to facilitate catalysis and electron
transfer reactions, the protein backbone of the enzyme has been shown to tune the redox [3] and
fluorescence properties of the flavin unit [4]. A variety of biomimetic model systems have been developed
to determine the specific role non-covalent interactions play in modulating these processes [5,6].
The optical and electronic properties of flavins make them excellent starting points for the design of
functional molecular systems. A number of examples of flavin derivatives that are covalently linked to
other acceptor systems have been reported that feature interesting and useful optical and electrochemical
properties [7,8]. Herein we report the synthesis and characterization of two acceptor-acceptor systems
that feature covalently linked naphthalenediimide (NDI) [9,10] and flavin moieties [11]. In these
compounds, the NDI unit is linked to the flavin through a short aromatic spacer group and is connected
to the flavin either at the N(10) or N(3) positions to afford compounds 1 and 2, respectively. While the
structures of these two materials are related, these two compounds let us compare conjugated (1) and
non-conjugated (2) flavin-NDI constructs