Photo-transformation trajectories of Nitro-Spiropyran in Hybrid Compounds with [60]Fullerene

Photo- and thermo- isomerization trajectories of various conversion pathways between nitro-spiropyran and its trans-trans-cis merocyanine form were produced and the role of nπ∗ states was investigated along the corresponding potential energy surface calculated using the ωB97XD functional and the cc-pVDZ basis set. The nondissociative nπ∗ states on the photoisomerization trajectories can switch from/to the dissociative photoactive ππ∗ state at two intersections between their energy surfaces. The photochromic properties inherited in hybrid compounds of nitro-spiropyran-containing [60]fullerene are interpreted due to a reversible "dual energy bypass" ππ∗→nπ∗ mechanism in terms of both adiabatic absorption and highly effective nonadiabatic dissipative transitions between the excited states of the photochromic fragment, that prevents energy loss through the [60]fullerene and in this way keeps the photochromic properties intact.