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

Abstract

A deep cavitand is used to encapsulate the aromatic molecule pyrene in its interior while also binding Tl 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 Tl recognition by the cavitand enhances the intersystem crossing and decreases the phosphorescence radiative lifetime from ∼30 to 0.23 s. The cavitand also decreases the rate of O 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 removal. Host:guest recognition provides a route to molecular-scale triplet emitters that can function under ambient conditions.

Selective Sensing of Phosphorylated Peptides and Monitoring Kinase and Phosphatase Activity with a Supramolecular Tandem Assay

“…For a fuller discussion, please see ref 25. When complexed, all three metals (Cu 2+ , Co 2+ , Ni 2+ ) cause significant quenching of 1•3 by the heavy-atom effect. 28 The quenching amount is relatively consistent once fully bound: the major variable between each is the affinity of the metal for the 1• 3 complex. Addition of metals will affect the affinity of 1•3 for the peptide/phosphopeptide (presumably enhancing the affinity for phosphopeptide via charge matching), as well as the emission of 3 when bound to the host.…”

Supramolecular Crowding Can Avoid Oxygen Quenching of Photon Upconversion in Water

“…One of the serious problems of aqueous TTA‐UC is quenching of excited triplet states by dissolved molecular oxygen. Although the suppression of oxygen quenching has been reported in several host–guest systems, these works mainly focused on the single‐exciton phosphorescence process and their design concept can not be simply extended to multi‐exciton TTA‐UC, which requires triplet exciton diffusion in multichromophore systems. By encapsulating UC chromophores in viscous organic liquids or rubbery matrices, oxygen diffusion was slowed down .…”

Room-Temperature Phosphorescence from Encapsulated Pyrene Induced by Xenon

“…However, the value of the heavy atom effect has been established in supramolecular assemblies (micelles, cyclodextrins, zeolites, and silica), − which by confining the aromatic guest molecules and protecting their excited state from the quencher oxygen , also bring the heavy atom (or ion) closer to elicit room temperature phosphorescence of the guest aromatic molecule. Unlike Tl + , the heavy atom valued for bringing about phosphorescence at room temperature from supramolecular encapsulated guests including in the recent example with an organic cavitand and pyrene as the host and guest, respectively, and heavy atom xenon, soluble in isotropic solvents, has attracted little attention . Although xenon’s effect on intersystem crossing (S 1 to T 1 and T 1 to S 0 ) is well documented, − very few publications mention about xenon-induced phosphorescence in solution at room temperature.…”

“…Recent upsurge − in “up-conversion”, a process prompted by triplet–triplet annihilation, has led to exploring new methods in enhancing the generation of molecules in their triplet states (T 1 ) at room temperature in solution. − Though the theory of the “heavy atom effect”, one of the well-known methods to enhance triplet yields of aromatics in solution due to Kasha and his co-workers is well understood, − and its usefulness in inducing phosphorescence in isotropic solution is limited due to quenching of the triplets by dissolved oxygen. However, the value of the heavy atom effect has been established in supramolecular assemblies (micelles, cyclodextrins, zeolites, and silica), − which by confining the aromatic guest molecules and protecting their excited state from the quencher oxygen , also bring the heavy atom (or ion) closer to elicit room temperature phosphorescence of the guest aromatic molecule.…”

“…Although xenon’s effect on intersystem crossing (S 1 to T 1 and T 1 to S 0 ) is well documented, − very few publications mention about xenon-induced phosphorescence in solution at room temperature. The continued interest on room-temperature phosphorescence employing supramolecular assemblies motivated us to examine the process using octa acid (OA, Figure b) , as the host and xenon and Tl + as the heavy atom perturbers. In addition, our interest in energy, electron, and spin transfer across the OA capsular wall , prompted us to explore the possibility of singlet–triplet spin perturbation by heavy atoms under similar circumstances. − …”