The second pathway involves internal conversion from the S2(ππ*) state to the S1(nπ*) state, followed by intersystem crossing to the T1(ππ*) state. The participation of the first pathway can be supported by the slight blueshift and increase in intensity of the transient species as a function of time delay (Figure ). This slight blueshift and increase in intensity is characteristic of conformational relaxation and vibrational cooling dynamics. The excited state optimizations predict that the sulfur atom in the T2(nπ*) state exhibits significant puckering compare to that of the T1(ππ*) planar minima (Figure ). Thus, it is possible that the slight blueshift and increase in intensity observed in the transient spectra is associated not only with vibrational cooling in the T1(ππ*) state (E(T2 -T1) ~ 1 eV), but also with conformational relaxation dynamics upon internal conversion from the T2(nπ*) state to the T1(ππ*) planar minima. We further note that large blueshift and increase in intensity are not observed in the transient spectra. This could be due to a significant fraction of the T2(nπ*) state population being able to internally convert to the out-of-plane T1(ππ*) minima, in which the sulfur atom is also out of the plane of the purine chromophore and conformational relaxation is not expected to play a major role. The participation of the indirect intersystem crossing pathway is supported by the observation that the calculated absorption spectrum of the S1(nπ*) state is in good agreement with the experimental transient absorption species initially observed in Figure . Hence, we conclude that both direct and indirect intersystem crossing pathways contribute to the efficient population of the T1(ππ*) state of 6MP.