Water-Dispersible Triplet–Triplet Annihilation Photon Upconversion Particle: Molecules Integrated in Hydrophobized Two–Dimensional Interlayer Space of Montmorillonite and Their Application for Photocatalysis in the Aqueous Phase

Abstract

Green incident light (λ = ∼500 nm) is converted to blue light (λ = 400–450 nm) in air using bulky alkylammonium (DMDOA+), 9,10-diphenylanthracene (DPA), and Ru­(dmb)3 2+ (dmb = 4,4′-dimethyl-2,2′-bipyridine) intercalated in a layered clay compound called “montmorillonite” [MMT–DMDOA+–DPA–Ru­(dmb)3 2+]. The two-dimensional interstitial space has an interlayer spacing of a few nanometers. Emitter DPA is present in this interlayer spacing, having an intermolecular distance of approximately 3.0 nm at a high concentration. Sensitizer Ru­(dmb)3 2+ is relatively dilute, having an intermolecular distance of 47 nm. The emission decay measurements and quantitative evaluation of the emission intensity demonstrate that blue light emission is induced by sequential processes, which consist of a triplet–triplet (T–T) energy transfer reaction from Ru­(dmb)3 2+ to DPA and T–T annihilation of DPA molecules. From thermogravimetry and Fourier transform infrared spectra measurements, we observe that the cointercalated alkylammonium acts as a waterproof agent to prevent quenching of the molecules in the excited triplet states by H2O. Finally, we demonstrate a photocatalytic decomposition of Rhodamine B dissolved in H2O-containing MMT–DMDOA+–DPA–Ru­(dmb)3 2+ and Pt-deposited WO3 photocatalyst, where wavelength of incident light (λ > 440 nm) is longer than the absorption edge of WO3 photocatalyst. The mechanism of photocatalytic decomposition is the following: (i) the incident long wavelength light is upconverted to 400–450 nm light by MMT–DMDOA+–DPA–Ru­(dmb)3 2+, and then, (ii) WO3 photocatalyst is excited by the generated 400–450 nm light, and finally, (iii) Rhodamine B is decomposed on the Pt cocatalyst induced by the holes in a valence band of WO3.

Tuning the Quantum Dot (QD)/Mediator Interface for Optimal Efficiency of QD-Sensitized Near-Infrared-to-Visible Photon Upconversion Systems

“…Quantum dot (QD)-sensitized photon upconversion has achieved high upconversion quantum yields (QYs) − and received increasing attention in recent years because of the desirable properties of QD sensitizers, ,− including their tunable band gap from the visible region to the near-infrared spectral region, nearly degenerate singlet/triplet excitons at room temperature, easily modified surface chemistry, and long exciton lifetimes . Similar to well-established polymer upconversion systems − and other triplet–triplet annihilation (TTA)-based upconversion devices, − in a typical QD-sensitized photon upconversion system (Figure A), the photogenerated excitons in the QD are transferred sequentially to the surface-bound triplet mediator and then the emitter in solution, and two excited emitters collide and undergo TTA to form a bright singlet excited state (and a ground-state emitter), from which a higher-energy photon is emitted. , The total upconversion QY (UCQY) can be expressed as the product of the QYs of these individual steps Here, Φ ex is the triplet exciton generation QY of the QD sensitizer, which is close to unity because the strong spin–orbital angular momentum coupling in QDs mixes singlet and triplet spin characters in exciton states; Φ TET1 is the QY of triplet energy transfer (TET) from the excited QD to the adsorbed mediator; ,,− Φ TET2 is the QY for TET from the adsorbed mediator to the emitter in the solution; Φ TTA is the TTA QY; and Φ FL is the QY of singlet fluorescence, which is often close to unity . Here, the maximum UCQY is 100% when two photons are converted into one photon in accordance with our previous reports.…”

Recent advances in materials for and applications of triplet–triplet annihilation-based upconversion

“…[98][99][100] The application of TTA-UC with photocatalysts in water can contribute to efficient environmental remediation as in the above-described air conditions, but TTA-UC is mainly used by insoluble chromophores, and triplet states are easily quenched when exposed to oxygen. 101 Therefore, Kim et al developed aqueous dispersible TTA-UC microcapsules on WO 3 loaded with Pt to maintain a core-shell structure. 4 These TTA-UC microcapsules show both Stokes-and anti-Stokes emission under green-light excitation because the rigid polymer preventing diffusion between PtOEP/DPA and UC was eliminated (Fig.…”

Dense Integration of Stable Aromatic Radicals within the Two-Dimensional Interlayer Space of Clay Minerals via Clay-Catalyzed Deamination of Arylammoniums

“…From the XRD patterns of 1AA_SA_RT_boiled and 2AA_SA_RT_boiled (Figure d), the interlayer distance of the clay compounds is not changed through the treatment, suggesting that the layered structure was not delaminated or swollen by the treatment. It can be considered that the interlayer space of SA was hydrophobized by the intercalation of aryl species, and thus H 2 O cannot invade the interlayer space . Consequently, the aryl radicals can survive the harsh condition of H 2 O reflux due to a protective role of the precise layered structure of SA.…”

“…It can be considered that the interlayer space of SA was hydrophobized by the intercalation of aryl species, and thus H 2 O cannot invade the interlayer space. 25 Consequently, the aryl radicals can survive the harsh condition of H 2 O reflux due to a protective role of the precise layered structure of SA.…”