Spatial isomerism regulates host-guest distance for highly efficient organic room-temperature phosphorescence.

The host-guest organic room-temperature phosphorescent (RTP) materials based on Dexter triplet-triplet energy transfer (TTET) have demonstrated significant application potential in fields such as anti-counterfeiting, information encryption, and stimulus-responsive sensing. Nevertheless, most reported RTP materials have focused on tuning host-guest energy-level alignment. Strategies capable of structurally manipulating host-guest distances at the molecular level remain exceedingly rare. Herein, a spatial isomerism strategy is employed that precisely modulates the distance between host and guest molecules, thereby significantly increasing the phosphorescence quantum yield from 0.81% to 8.97% and extending the lifetime from 23 to 158 ms through enhanced TTET. Among the doped systems, the crystal structure and electronic properties of the guests indicate that the degree of distortion and electrostatic complementarity determine the phosphorescence quantum yield. Further quantum mechanics/molecular mechanics calculations quantitatively reveal that the host-guest average distance can be compressed from 3.36 Å to 2.86 Å, thereby enhancing the distance-sensitive TTET process and achieving a simultaneous increase of more than one order of magnitude in phosphorescence performance. In addition, all the doped systems exhibit significant acid-base stimulus-responsiveness, enabling reversible control of phosphorescent color. This tunability provides the possibility for constructing multi-level environment-responsive anti-counterfeiting and information encryption platforms.