Crystal stacking analysis and simulated calculations for dynamic ultralong organic phosphorescence of PyCz. (a) The intermolecular interactions around one molecule in PyCz-B and PyCz-N before and after long photoactivation in crystalline state measured at 100 K, the green dash line refers to the initial interactions and the red dash line is the added interactions after long photoactivation. (b) The π-π overlap and distance of selected dimer with π-π interactions in PyCz-B(i) and PyCz-N(i). Note that the green isosurface refer to the calculated molecular interactions by IGM, the isovalue is 0.008. (c) The free volume region (cyan isosurface) in single crystal cells of PyCz-B(i) and PyCz-N(i). (d) The calculated change of single molecular energy in PyCz-B and PyCz-N during the process of photoactivation. (e) Proposed mechanism for different dynamic speeds of dynamic UOP in polymorphs.