Room-Temperature Phosphorescence from Encapsulated Pyrene Induced by Xenon

Abstract

Phosphorescence from pyrene especially at room temperature is uncommon. This emission was recorded utilizing a supramolecular organic host and the effect due to the heavy atom. Poor intersystem crossing from S1 to T1, small radiative rate constant from T1, and large rate constant for oxygen quenching hinder the phosphorescence of aromatic molecules at room temperature in solution. In this study, these limitations are overcome by encapsulating a pyrene molecule within a water-soluble capsule (octa acid, OA) and purging with xenon. While OA suppressed oxygen quenching, xenon enabled the intersystem crossing from S1 to T1 and radiative process from T1 to S0 through the well-known heavy atom effect. The close interaction facilitated between the pyrene and the heavy atom perturber xenon in the three-component supramolecular assembly (OA, pyrene, and xenon) resulted in phosphorescence from pyrene. Computational modeling and NMR studies supported the postulate that pyrene and more than one molecule of xenon are present within a confined space of the OA capsule.

Co-facial π–π Interaction Expedites Sensitizer-to-Catalyst Electron Transfer for High-Performance CO2 Photoreduction

“…The underlying spin-free states, for example, S 1 , T 5 , and T 6 , feature pronounced spin–orbit coupling (SOC) of up to nearly 1000 cm –1 ( Tables S2–S7 ), indicating that the triplet states in IrPPPY are rapidly accessible upon ultrafast intersystem crossing. 56 …”

“…Furthermore, and typically for structurally related Ir complexes, the visible-light absorption at around 450 nm shows a weakly absorbing spin-forbidden 1/3 MLCT transition, which can be assigned according to the simulations to an excitation into SO 7 (at 478 nm, 2.59 eV)a mixed MLCT transition to both ppy/pppy ligand spheres. The underlying spin-free states, for example, S 1 , T 5 , and T 6 , feature pronounced spin–orbit coupling (SOC) of up to nearly 1000 cm –1 (Tables S2–S7), indicating that the triplet states in IrPPPY are rapidly accessible upon ultrafast intersystem crossing …”

“…The underlying spin-free states, for example, S 1 , T 5 , and T 6 , feature pronounced spin−orbit coupling (SOC) of up to nearly 1000 cm −1 (Tables S2−S7), indicating that the triplet states in IrPPPY are rapidly accessible upon ultrafast intersystem crossing. 56 Next, steady-state fluorescence experiments for the emission of Ir PSs were implemented at room temperature in Ar-saturated anhydrous CH 3 CN (Figure 2b). We noticed that the presence of ambient or even traces of air can efficiently quench the fluorescence intensity of both Ir complexes, demanding the degassing of measured solutions.…”

Ultrafast Excited State Dynamics of Spatially Confined Organic Molecules

“…Expectedly, no phosphorescence was detected in solution at room temperature. In this context, the value of “confined space of the OA capsule” in stabilizing the triplet state property became useful. − The steady-state emission spectra at room temperature for the 1:2 complex 3I-C-1@OA 2 revealed a low-intensity red-shifted band, which intensified with a decrease in the temperature, along with the normal emission band (Figure a,b). This new band matches with the phosphorescence of 3I-C-1 recorded at 77 K (Figure c), and assigned as the room temperature phosphorescence of 3I-C-1@OA 2 .…”

Heavy-element-free triplet accessibility in pyrene-core compounds at room temperature by microcrystal engineering

“…Hence, to enhance the internal quantum efficiency (IQE) of a device, triplet harvesting is indispensable. 25,26 In this context, the compound pyrene is like a ''sprinting horse'' because of its rapid decay. It is, thus, a challenging task to slow down the decay process since the large singlet-triplet energy gap does not allow spin-forbidden intersystem crossing (ISC).…”