Modulating the crystal packing to achieve efficient ultralong organic phosphorescence by simple methylation engineering

Abstract

Molecular stacking plays a critical role in ultralong organic phosphorescence (UOP) generation under ambient conditions. To better understand how the crystal packing affects UOP and achieve efficient UOP, herein, a combined experimental and theoretical study of the synthesized S,S-dioxide phenothiazine derivatives was performed, in which methyl groups with different numbers and substitution sites were used to modulate the solid-state packing. All compounds showed similar photophysical characteristics in solution, but distinct UOP behaviors in the crystalline state. m-DMOPP crystals possessing two methyl moieties and densely ordered stacking can achieve a longer lifetime of 375 ms and higher phosphorescent efficiency. The potential applications in anticounterfeiting and 3D patterning based on m-DMOPP were realized in virtue of its excellent UOP character. Importantly, the changes in displacement between adjacent molecules along the Y-axis had a more significant impact on the intersystem crossing process than that along the Z-axis in such H-aggregation phenothiazine-based materials. Our investigation would provide a profound understanding of the relationship between molecular stacking and UOP properties and a feasible molecule strategy to design ideal UOP materials.