1 ππ* → S0 internal conversion (primary pathway). Importantly, however, with a lifetime value of 7.1 0.2 ps, and consistent with the five-fold larger fluorescence yield of 5mCyd compared to Cyd, the decay lifetime of the S1 ππ* state in 5mCyd is 5 longer than that observed for Cyd, suggesting an energetic barrier might retard access to the S1/S0 ethylenic twisting CI. This idea is supported by quantum chemical calculations that demonstrated an energetic barrier of ca. 0.1 to 0.3 eV between the bent global minima and S1/S0 ethylenic twist CI of 5mCyd compared to an barrier of 0.1 for Cyd. We also note that our reported S1 lifetime for 5mCyd is in good agreement with that previously reported by Sharonov et al., Ma et al., Wang et al., Martínez-Fernández et al., and Malone et al. using time resolved fluorescence and absorption spectroscopies.