The species formed by the reduction of BTDN in a one-electron fashion generated a new peak at 2185 cm -1 and a bleach at 2238 cm -1 in the IR spectra (Figure ). This is assigned to the shift of the C≡N stretching mode as electron density is accumulated on the molecule, it also fits the mode that we have previously assigned to the BTDN •-species. In the second reduction wave the peak shifts to even lower wavenumbers, the peak appears at 2111 cm -1 and is assigned to the BTDN 2-anion that has also previously been detected in UV-Vis SEC. In presence of 2 bar of 0.8% CO2 (corresponding to 4.32 mM CO2), reduction of BTDN to BTDN •-is unaffected by the presence of CO2, as evident by the formation of a band at 2185 cm -1 (Figures ) that is identical to that observed under Ar (Figure ). On the other hand, further reduction of BTDN is observable at the same potential region corresponding to reoxidation of BTDN 2-to BTDN •-. This process appears to have slower kinetics compared to that observed under Ar atmosphere. At the same time, there is a slow decrease in intensity of the bands at 2214 cm -1 , 1645 cm -1 , and 1684 cm -1 , along with a slow increase in the intensity of the 2342 cm -1 band. These observations suggest that the reaction between BTDN 2-and CO2 may be reversible. An oxidation peak is observable at more positive potential (-1.04 V) and this corresponds to oxidation of BTDN •-, verified by the depletion of the corresponding band at 1985 cm -1 . At higher CO2 partial pressure (100% CO2, 3 bar), reduction of BTDN follows a similar trend. There is no observable reaction between BTDN •-and CO2 (Figure ). Upon further reduction of BTDN •-at the second reduction wave, there is no observable BTDN 2-intermediate at 2111 cm -1 , suggesting higher rate for the reaction between BTDN 2-and CO2 when the concentration of CO2 is in large excess. Similarly, the band at 2142 cm -1 is not observable, consistent with assignment of this band to an intermediate species formed by the reaction between BTDN 2-and CO2. The band at 2214 cm -1 is observable under excess of CO2, and the ratio of intensity between the 2214 cm -1 and the 2185 cm -1 band is comparable to that observed under very low CO2 partial pressure (0.8% CO2, 2 bar). This suggests that the 2214 cm -1 band may be attributed to a side product that does not involve reaction with CO2, as the formation of this species does not appear to be influenced by CO2 concentration. At the C-O stretching region, there are additional bands formed at 1739 cm -1 and an apparent peak at 1676 cm -1 . Notably, the relative intensities of the bands in the 1600-1700 cm -1 region are very distinct between low and high CO2 partial pressures, suggestive of multiple carbonyl species formed. The ratio of peak reduction current ip2/ip1 between low and high CO2 partial pressure in IR-SEC experiments (Figures and) is not significantly different, indicating little dependency on CO2 concentration. This suggests that reaction between BTDN 2- and CO2 is not likely to be catalytic. To gain additional insight into the reaction between BTDN 2-and CO2, potential step SEC experiments were carried out where BTDN is cycled between -2.1 V and -0.8 V under low CO2 partial pressure (0.8% CO2,1.5 bar) (Figure ). The band at 2142 cm -1 appears as a transient species. Intriguingly, an additional band at 2080 cm -1 is observable. The wavenumber of the 2080 cm -1 band is lower than that of BTDN 2- (2111 cm -1 ), suggesting that it corresponds to a further reduced species of adduct between BTDN 2-and CO2. Since this species is observable in potential step experiments but not in scanning SEC experiment, it is likely that it is a reduction product of a transient species formed by reaction between BTDN 2-and CO2. Since there are no discernible additional redox peak, the reduction potential of this transient species is likely to be slightly more negative than the reduction potential of BTDN •-. In scanning SEC experiments, this transient species undergoes further chemical reaction before the potential is scanned sufficiently negative to enable its reduction, thereby precluding its formation. A plausible candidate may be reduction of the transient species with ν(CN) stretching frequency at 2142 cm -1 to form a further reduced species with ν(CN) frequency at 2080 cm -1 .