Boosting the Heavy Atom Effect by Cavitand Encapsulation: Room Temperature Phosphorescence of Pyrene in the Presence of Oxygen

A deep cavitand is used to encapsulate the aromatic molecule pyrene in its interior while also binding Tr ions with its terminal carboxylates. Steady-state and time-resolved spectroscopic experiments, along with quantum yield measurements, quantify the enhancements of intersystem crossing and room temperature phosphorescence due to cavitand encapsulation. These results are compared to those obtained for pyrene contained in sodium dodecyl sulfate micelles, which is the usual system used to generate room temperature phosphorescence. The combination of selective binding and strong Tr recognition by the cavitand enhances the intersystem crossing and decreases the phosphorescence radiative lifetime from similar to 30 to 0.23 s. The cavitand also decreases the rate of O-2 quenching by a factor of 100. Together, these factors can boost the room temperature phosphorescence signal by several orders of magnitude, allowing it to be detected in water without O-2 removal. Host:guest recognition provides a route to molecular-scale triplet emitters that can function under ambient conditions.