The full broadband transient absorption data for 5mCyd and Cyd were satisfactorily fitted with a two and three-component sequential kinetic model, respectively. The global, average lifetimes are reported in Table . Evolution associated difference spectra (EADS) and representative kinetic traces extracted from the global and target analyses of the solvent-corrected transient data are shown in Figure , while those under low photon density conditions are reported in Figures and. We remark that the transient data that are corrected for the solvent signal (i.e., under high photon density) and the transient data that do not require solvent correction (i.e., under low photon density) can be satisfactorily globally fit with the same set of lifetimes shown in Table . eV for Cyd. Therefore, following excitation at 267 nm, it is expected that both the S1 and S2 excited states could be populated simultaneously. In such a case, internal conversion from the S2 to S1 excited state is proposed to occur ultrafast, i.e., < 100 fs, and therefore, may not be observed within our experimental time resolution of approximately 250 fs. Hence, we assigned the first, instrument response-limited lifetime of 0.1 and 0.2 ps of each molecule to a movement along the S1 potential energy surface away from the FC region toward a local minimum. This is supported by the computational work by Martínez-Fernández et al. and Pepino et al. The former group found two minima for both 5mCyd and Cyd using TD-CAM-B3LYP/6-31(d) and MS-CASPT2(14,10)/ANO-L level of theory. The latter group also found the same two minima for Cyd, one planar and one bent minimum, and additionally a third minimum accessed after the S2/S1 conical intersection (CI), which has out-of-plane puckering at C4 with strong coupling to the 1 nO𝜋* excited state. The black EADS 1 in Figures and is therefore, assigned to a linear combination of the 1 ππ* planar, twist, and C4 out-of-plane puckered minima, and possibly with some contribution from the 1 nN* state, which is in good agreement with the simulated excited state absorption spectra (ESA) computed by Pepino et al. The small fluorescence quantum yield of ca. 10 for both molecules, lend support to the idea that the S1 minimum of both 5mCyd and Cyd is fairly shallow. For Cyd, we propose two primary relaxation pathways occur from the S1 minimum: (1) fluorescence and (2) S1 𝜋𝜋* → S0 internal conversion. This competitive process is assigned to the second lifetime of 1.4 0.1 ps. The decay of the 1 ππ* via fluorescence and internal conversion is in good agreement with those reported previously for cytosine, where the conical intersection is accessed through out-of-plane ethylenic twisting of the C5-C6 bond. The red EADS 2 (Figures and) is assigned to a combination of the 1 ππ* twist and C4 out of plane puckered minima. Lastly, the third lifetime of 43.7 8.1 ps for Cyd is assigned to nonradiative decay of the 1 nN* state, which is also in good agreement with the lifetime previously reported in literature. It has been suggested that in cytosine the 1 nN* state is accessed near the FC region, however, it is still unclear if internal conversion originates from the S1 ππ*, S2 ππ*, or from both states. The blue EADS 3 (Figure ) is therefore primarily assigned to the absorption of the 1 nN* minimum, which is supported by the ESA of the 1 nN* minimum predicted by Pepino et al. Quantum chemical calculations for cytosine and 1-methylcytosine that includes explicit water molecules have shown that the 1 nO* state is significantly higher in energy and should not be populated upon excitation at 267 nm. However, we cannot rule out unequivocally a small participation of the 1 nO* state (see discussion in the SI). We remark that a triplet quantum yield of about 1% has been proposed for cytosine in aqueous solution. If such a small fraction of the population reaching the 1 nN* state in Cyd is indeed able to intersystem cross to the triplet sate, it is possible that we are unable to detect it within the sensitivity of the spectrometer. We note, however, that while decay channels involving intersystem crossing to the triplet manifold have been investigated computationally for Cyd, there is currently minimal experimental evidence and no computational evidence supporting the population of the triplet state in Cyd in aqueous solution. Furthermore, the transient absorption experiments by Wang et al. and Ma et al. do not observe the population of a triplet state, in agreement with our results. with a small amount of the excited state population decaying via fluorescence. Similar to Cyd, the second lifetime is assigned to a competitive process between fluorescence (minor pathway) and S1