We first investigate the real-time absorbance of the 1,5-BTMAPAQ species by integrating an in situ ultraviolet-visible (UV-Vis) spectrometer into the electrolyte flow path in an operating flow cell, as illustrated in Figure . Figure presents the absorbance spectra of 5 mM 1-5,BTMAPAQ in 1 M KCl within a flow cell, operating against 20 mM BTMAPFc under a 100% N2 stream to capture the real-time absorbance profiles during reduction of 1,5-BTMAPAQ in the absence of any 1,5-BTMAPAQ(CO2)2 2- adduct. Under these conditions, five distinct peaks at wavelengths of 223 nm, 251 nm, and 391 nm, 487 nm and 523 nm are evident. During charging, the 223 nm peak decreases in absorbance, and the 251 nm and 391 nm peaks increase, with a new peak emerging at 430 nm, corresponding to the conversion of the molecule from its oxidized form to the reduced form. Subsequently, the battery was brought to rest, and UV-Vis spectra were monitored as a 50% CO2/50% N2 stream is introduced to form the adduct (Figure ). This methodology enabled the acquisition of spectra for both the reduced 1,5-BTMAPAQ and the 1,5-BTMAPAQ(CO2)2 2-adduct species within the same experiment. Comparing the spectra at t = 0 and after half an hour of CO2 purging, we observed minor absorbance changes, particularly at 251 nm, 391 nm and 487 nm, indicating a similarity between the spectra of the reduced species and the adduct, which poses a challenge for precise quantification of the species using this method. The full operation of the battery, involving charge and discharge cycles, was also conducted separately under N2 and CO2 environments in separate experiments, as illustrated in Figure . These experiments similarly revealed minor changes between the spectra under these conditions. Consequently, we shifted our focus to fluorescence spectroscopy to explore the potential of utilizing emission profiles as a means of differentiation. Figures 4c and 4d present the emission spectra of the oxidized, reduced, and adduct species of 1,5-BTMAPAQ, obtained ex situ using a fluorescent plate reader. The oxidized species underwent reduction in a flow battery against BTMAPFc within a glovebox, and the BTMAPAQ(CO2)2 2-adduct was prepared by introducing excess dry ice to the reduced solution inside the glovebox. Subsequently, the reduced, oxidized, and adduct forms of 1,5-BTMAPAQ were sealed in a transparent well plate and transferred to the plate reader (experimental details in SI Section 4.3). Figures and illustrate the emission spectra of species excited at 405 nm and 475 nm, respectively. In both cases, the oxidized species shows almost no fluorescence, whereas interestingly, both the reduced and the adduct species exhibit fluorescence, with the adduct form displaying significantly higher intensity. This intriguing trend doesn't appear to be unique to our molecule. We observed a similarly high fluorescence intensity in the adduct for other anthraquinones, including 2,2′-((9,10-dioxo-9,10-dihydroanthracene-2,6-diyl)bis(oxy))-dipropionic acid (2,6-D2PEAQ ) and 2-2-propionate ether anthraquinone (22PEAQ ), as demonstrated in Figure . Note that the solutions contain mixtures of different forms of the anthraquinone, for example the reduced solution contains the collection of 𝐴𝑄 2-as well as 𝐴𝑄𝐻 -and 𝐴𝑄𝐻 2 . This mixture may induce diverse energy transition states, influencing the emission intensity in response to varying excitation wavelengths. However, the noteworthy insight gathered from these figures is that, through a careful selection of emission wavelength regions, we can identify areas where the fluorescence signatures of the reduced, oxidized, and adduct species of 1,5-BTMAPAQ are distinct enough to potentially enable quantification of the BTMAPAQ(CO2)2 2-by careful selection of band-pass filters. Specifically, when considering an emission wavelength close to 520 nm for compounds excited at 405 nm (Figure ), we observe that the adduct form still exhibits high fluorescence, while the reduced species approaches the bottom of its emission peak. Conversely, selecting an emission wavelength near 600 nm for compounds excited at 475 nm (Figure ), we observe that the reduced form is at its peak intensity, while the adduct is at the bottom of the emission peak, displaying almost no fluorescence. Furthermore, the emission spectra of the pure bicarbonate/carbonate solutions do not show any fluorescence properties that differ from the background pH 14 solution, as depicted in Figure . This analysis based on the ex situ data suggests the possibility of leveraging the fluorescence signatures of these compounds for a dynamic, precise, and realtime exploration of the nucleophilicity-swing mechanism by monitoring the BTMAPAQ(CO2)2 2-adduct concentration evolution during operation in isolation from the pH-swing mechanism.