Fig. 3: Proposed mechanism of photoisomerization/thermal relaxation process and HOMO/LUMO simulation of PMC and PSP.
From: An ultrawide-range photochromic molecular fluorescence emitter

a, b Gibbs free energy profile (kcal/mol) and schematic representation of the photoswitch isomerization mechanism (obtained by M06-2X/6-311 + G(d,p)//M06-2X/6-31 + G(d,p)). c The frontier molecular orbitals of PMC and PSP (optimized by B3LYP/6-31 + G). (TS: transition state, G: Gibbs free energy).