With compounds 1-4 in hand, we compared their photophysical properties to their parent fluorophores (Figure ). In all cases the attachment of indolequinone 8 or 9 to the dye led to an almost complete reduction in fluorescence intensity for all three dyes. Probe 1 displays more than 8-fold decrease of its emission intensity compared to DDAO, while probes 2, 3, and 4 exhibit no detectable emission signal compared, as expected. To investigate the electrochemical properties of the probes and compare these to their parent dyes we next conducted cyclic voltammetry (CV) experiments (Supporting Information). Compounds 11, 3, and 4 have similar voltammograms, which show a single irreversible peak at a reduction potential of -1.21 V (vs Ag/AgNO3) (Figure ). This is consistent with reduction of the indolequinone component of these molecules, followed by fragmentation (i.e., an irreversible chemical reaction), and indicates that the bioreduction of these compounds should occur under similar conditions (Figure ). Compounds 1 and 2 have more complex voltammograms that contain multiple reductions peaks. As these peaks are not present in the parent indolequinone or dye voltammograms, this indicates that coupling of the compounds together affects their electrochemical and redox properties, in part by removing the ability of the phenolate to delocalize into the conjugated π-system of the dyes. Compound 1 displays two reversible reduction peaks at -0.8 and -1.27 V (vs Ag/AgNO3), while 2 displays two pseudo-reversible reductions at -1.06 and -1.27 V (vs Ag/AgNO3). The least negative reduction peaks of 1 and 2 likely correspond to reduction of the indolequinone and indicates that both of these compounds should undergo more facile bioreduction than 11, 3, or 4. The presence of additional reductions in the voltammograms for compounds 1 and 2 indicates that their redox chemistry is more complicated and that this could impact on their behavior in a biological setting.