Harnessing Heavy-Atom Effects in Multiple Resonance Thermally Activated Delayed Fluorescence (MR-TADF) Sensitizers: Unlocking High-Performance Visible-to-Ultraviolet (Vis-to-UV) Triplet Fusion Upconversion.

Ultraviolet (UV) light plays a crucial role in various applications, but currently, the efficiency of generating artificial UV light is low. The visible-to-ultraviolet (Vis-to-UV) system based on the triplet-triplet annihilation upconversion (TTA-UC) mechanism can be a viable solution. Metal-free multiple resonance thermally activated delayed fluorescence (MR-TADF) materials are ideal photosensitizers (PSs) apart from the drawback of high photoluminescence quantum yields (PLQYs). Herein, we systematically investigated the impact of the heavy-atom effect (HAE) on the MR-TADF sensitizers. BNCzBr was then synthesized by incorporating a bromine atom into the skeleton of the precursor BNCz. Impressively, the internal HAE (iHAE) leads to a significantly decreased PLQY and a remarkably increased intersystem crossing quantum yield (ΦISC). Consequently, a higher upconversion quantum efficiency of 12.5% was realized. While the external HAE (eHAE) harms the UC performance. This work guides the further development of MR-TADF sensitizers for high-performance Vis-to-UV TTA-UC systems.

Ultrafast Response Organic Photoswitch Materials and Their Application in Volumetric 3D Display.

Volumetric three-dimensional (3D) display technology based on static screens is a crucial branch of 3D displays. The essential component in volumetric 3D displays is selectively excitable display media that can generate voxels at any position. Here, we synthesized a series of organic photoswitch materials to meet the specific requirements of 3D display mediums. In these photoswitch solutions, voxels are activated ultrafast within tens of picoseconds at the intersection of two control lasers and faded rapidly within tens of milliseconds when switching light is turned off. An experimental volumetric 3D display system utilizing an organic photoswitch solution as a screen is demonstrated. The system not only achieves a dynamic 3D display but also enables 360° viewing. The volumetric 3D display system can display true 3D images without auxiliary glasses and is expected to be applicable in fields as diverse as virtual reality, medical imaging, architectural design, and military visualization.

Photochemically deoxygenating micelles for protecting TTA-UC against oxygen quenching.

Pluronic F127, P123 and cross-linked F127 diacrylate micelles are photochemically deoxygenating nanocapsules in which oxygen could be removed by photochemical reaction with a surfactant and efficient triplet-triplet annihilation photon upconversion (TTA-UC) can be achieved in air. The efficiency of TTA-UC under air is comparable to that under deoxygenated conditions.

Circularly polarized chemiluminescence from planar chiral bis(adamantylidene-1,2-dioxetane)s.

Bis(adamantylidene-1,2-dioxetane), upon conjugation to a planar chiral scaffold of [2.2]paracyclophane, gave chemical-triggerable circularly polarized chemiluminescence with a dissymmetry factor of 1.1 × 10-3 scale, to which exciton chirality upon chemiexcitation was assigned as the origin.

Luminescent Materials for Volumetric Three-Dimensional Displays Based on Photoactivated Phosphorescence.

True three-dimensional (3D) displays are the best display technologies and their breakthrough is primarily due to advancements in display media. In this paper, we propose two luminescent materials for a static volumetric 3D display based on photoactivated phosphorescence. The luminescent materials include (1) dimethyl sulfoxide (DMSO)/1-methyl-2-pyrrolidinone (NMP) or tetramethylene sulfoxide (TMSO) as the solvent and photochemically-deoxygenating reagent; (2) a metal phthalocyanine complex as the sensitizer; (3) a phosphorescent platinum complex as the emitter. The metal phthalocyanine complex, PdPrPc (PdBuPc), absorbs the light beam of 635 nm and the solvent scavenges the sensitized singlet oxygen. Light beams pass through a deoxygenated zone. The phosphorescent emitter, PtNI, absorbs the 440 nm light beam and phosphoresces only in the deoxygenated zone generated by the sensitizer. Phosphorescent voxels and high-contrast 3D images are well-defined at the intersection of 635 and 440 nm light beams.

Photochemically deoxygenating gels for triplet-triplet annihilation photon-upconversion performed under air.

For an efficient triplet-triplet annihilation photon upconversion (TTA-UC) process, matrices in which sensitizers and emitters are dispersed should not only allow molecular diffusions but also protect triplet excited states from oxygen-quenching. In this work, two photochemically deoxygenating gels, a poly(N-vinyl-2-pyrrolidone) (PVP) gel and a limonene gel, were prepared for TTA-UC performed under air. These two gels are optically transparent in the visible region and can serve as a scavenger for sensitized singlet oxygen. For the green-to-blue couple of platinum(II) octaethylporphyrin (Pt(OEP)) and 9,10-diphenylanthracene (DPA), under air, the bimolecular quenching rate constants were 6.73 × 108 dm3 mol-1 s-1 for the PVP gel and 1.54 × 109 dm3 mol-1 s-1 for the limonene gel, and the upconversion quantum yields were 9.1% and 1.9% in PVP and limonene gels, respectively. As matrices, the PVP gel can be employed in NIR-to-yellow, red-to-cyan, green-to-blue and blue-to-violet TTA-UC systems operating under air. TTA-UC systems of Pt(OEP)/DPA in PVP or limonene gels showed strong upconverted emission under air with non-coherent light of low optical power density as the excitation source.

Host-Guest Complexation-Induced Aggregation Based on Pyrene-Modified Cyclodextrins for Improved Electronic Circular Dichroism and Circularly Polarized Luminescence.

Several γ-cyclodextrin (CD) derivatives mono- or di-substituted by pyrenes at the primary rim of the CD were demonstrated to aggregate into nano-strips in aqueous solutions, with the pyrene moieties interpenetrating into γ-CD cavities. The hydrophobic complexation-induced aggregation provides a rigid chiral environment for the pyrenes and leads to significant electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) activities, giving unprecedently high gabs and glum values up to 4.3×10-2 and 5.3×10-2 , respectively. The aggregates lead to excimer emission with high quantum yields and show BCPL and BiCPL up to 338. 6 M-1 cm-1 and 169.3 M-1 cm-1 , respectively.

γ-Cyclodextrin-based [2]rotaxane stoppered with gold(I)-ethynyl complexation: phosphorescent sensing for nitroaromatics.

A [2]rotaxane is assembled by γ-cyclodextrin (γ-CD) with threaded 1,4-diethynylbiphenyl and bulky Au(I)-phosphine stoppers. The phosphorescence of the [2]rotaxane has been observed in aerated aqueous solution and found to be quenched by nitroaromatics due to γ-CD-based co-binding, providing a sensitive approach towards explosive-sensing.

A Prototype of a Volumetric Three-Dimensional Display Based on Programmable Photo-Activated Phosphorescence.

A proof-of-principle prototype of a volumetric 3D-displaying system is demonstrated by utilizing the photo-activated phosphorescence of two long-lived phosphorescent metal-porphyrins in dimethyl sulfoxide (DMSO), a photochemically deoxygenating solvent. The first phosphorescent sensitizer, Pt(TPBP), absorbs a light beam with a wavelength of 635 nm, and the sensitized singlet oxygen is scavenged by DMSO. The second phosphorescent emitter, Pt(OEP), absorbs a light beam with a wavelength of 532 nm and visibly phosphoresces only in the deoxygenated zone generated by the first sensitizer. The phosphorescent voxels, 3D images, and animations are well-defined by the intersections of the 635-nm and 532-nm light beams that are programmable by tuning of the excitation-power densities, the beam shapes, and the kinetics. As a pivotal selection rule for the phosphorescent molecular couple used in this 3D-displaying system, their absorptions and emissions must be orthogonal to each other, so that they can be excited and addressed independently.

Photo-writing self-erasable phosphorescent images using poly(N-vinyl-2-pyrrolidone) as a photochemically deoxygenating matrix.

A passive photo-writing approach for optical data recording is described. Poly(N-vinyl-2-pyrrolidone) has been demonstrated as a photochemically deoxygenating polymeric matrix in which phosphorescent images from a molecular phosphor could be written by photo-activation and be competitively erased by diffusional oxygen quenching.

A cyclometalating organic ligand with an Iridium center toward dramatically improved photovoltaic performance in organic solar cells.

Organometallic compounds as photoactive materials are relatively new in organic solar cells. Upon cyclometalation, the octahedral heteroleptic Ir complex TBzIr exhibits significantly enhanced optical-absorption and improved film-morphology compared to the planar organic 2-(5''-hexyl-[2,2':5',2''-terthiophen]-5-yl)benzo[d]thiazole (TBz) ligand. Thus, a dramatically improved power conversion efficiency (PCE) from ∼0 to 3.81% is attained when combined with PC71BM.

Photochemically deoxygenating solvents for triplet-triplet annihilation photon upconversion operating in air.

Sulfoxides and cyclic ureas are photochemically deoxygenating solvents in which the oxidative stress could be released and efficient triplet-triplet annihilation photon upconversion (TTA-UC) can operate in air. Such solvents can be practically screened out by harnessing the property of photo-activated phosphorescence.

Reversible Photoactivated Phosphorescence of Gold(I) Arylethynyl Complexes in Aerated DMSO Solutions and Gels.

Phosphorescence in fluid solutions at ambient temperature is usually quenched by molecular oxygen via energy transfer, and singlet oxygen is concomitantly sensitized. The long-lived phosphorescence of a series of AuI arylethynyl complexes with tunable emission energies in aerated dimethyl sulfoxide (DMSO) solutions can be completely and repeatedly switched on by controlled photoirradiation. A trace amount of DMSO oxidation by the sensitized singlet oxygen is proposed to lead to a depletion of molecular oxygen in the local microenvironment of the AuI phosphor in the photoactivation processes. Harnessing the photoactivated phosphorescence and using UV light as a non-contact pen, a writing-erasing-rewriting prototype has been demonstrated with a DMSO gel containing AuI arylethynyl complexes.

Efficient optical resolution of water-soluble self-assembled tetrahedral M4L6 cages with 1,1'-bi-2-naphthol.

In this paper, a water-soluble racemic self-assembled tetrahedral cage [Fe4L6](4-) was successfully resolved into their ΔΔΔΔ and ΛΛΛΛ enantiomers by (R)-/(S)-1,1'-bi-2-naphthol. The enantiomeric excess of the resolved Fe(II) cage was 99%.

Dynamic chiral-at-metal stability of tetrakis(d/l-hfc)Ln(III) complexes capped with an alkali metal cation in solution.

Chiral tetrakis(ß-diketonate) Ln(III) complexes Δ-[NaLa(d-hfc)(4)(CH(3)CN)] (1) and Λ-[NaLa(l-hfc)(4) (CH(3)CN)] (2) (d/l-hfc(-) = 3-heptafluo-robutylryl-(+)/(-)-camphorate) are a pair of enantiomers and crystallize in the same Sohncke space group (P2(1)2(1)2(1)) with dodecahedral (DD) geometry. Typically positive and negative exciton splitting patterns around 320 nm were observed in the solid-state circular dichroism (CD) spectra of complexes 1 and 2, which indicate that their shell configurational chiralities are Δ and Λ, respectively. The apparent bisignate couplets in the solid-state CD spectra of [CsLn(d-hfc)(4)(H(2)O)] [Ln = La (3), Yb (5)] and [CsLn(l-hfc)(4)(H(2)O)] [Ln = La (4), Yb (6)] show that they are a pair of enantiomers and their absolute configurations are denoted Δ and Λ, respectively. The crystallographic data of 5 reveals that its coordination polyhedron is the square antiprism (SAP) geometry and it undergoes a phase transition from triclinic (α phase, P1) to monoclinic (ß phase, C2) upon cooling. The difference between the two phases is brought about by the temperature dependent behaviour of the coordination water molecules, but this did not affect the configurational chirality of the Δ-SAP-[Yb(d-hfc)(4)](-) moiety. Furthermore, time-dependent CD, UV-vis and (19)F NMR were applied to study the solution behavior of these complexes. It was found that the chiral-at-metal stability of the three pairs of complexes is different and affected by both the Ln(3+) and M(+) ion size. The results show that the Cs(+) cation can retain the metal center chirality and stablize the structures of [Ln(d/l-hfc)(4)](-) or the dissociated tris(d/l-hfc)Ln(III) species in solution for a longer time than that of the Na(+) cation, and it is important that the Cs(+) ion successfully lock the configurational chirality around the Yb(3+) center of the complex species in solution. This is reasoned by the short Cs(+)···FC, Cs(+)···O-Yb and Cs(+)···Yb(3+) interactions observed in the crystal structure of α-5 and further confirmed by the chiral self-assembly of 5 or 6 from [Yb(H(2)O)(d/l-hfc)(3)] induced by CsI in a CHCl(3) solution.