Remarkable photo-induced crystal transition accompanying with room temperature phosphorescence change

Limited works are reported about photochromism type room temperature phosphorescence luminogens (RTPs) owing to notorious quenching effect and lacking of reliable guidance. Here we have demonstrated an organic crystal (4-iodophenyl terpyridine) exhibiting photochromism and slowly spontaneous heat recovery. The photochromic crystal can be formed within a few minutes, and it once formed is stable for hours. Fortunately, the single crystals before and after photochromism are all analyzable and clearly indicate molecular conformation and packing structure change. It is deduced that photoactivation has induced single bond internal rotations and intermolecular slipping to form a metastable crystal with more planar molecular conformation and looser stacking. The different molecular conformation and packing structure have changed intermolecular interaction nature, which should be responsible for their different RTP properties.