Impurities in Arylboronic Esters Induce Persistent Afterglow.

Several recent reports suggest that arylboronic esters can exhibit room temperature phosphorescence (RTP), an optical property that is desirable for applications in security printing, oxygen sensing, and bioimaging. These findings challenged the fundamental notion that heavy elements or changes in orbital symmetry were required for intersystem crossing to occur in organic compounds. As we had not observed long afterglow in the many arylboronic esters we had synthesized over many years, we suspected that the RTP observed in these systems had a simpler explanation: the materials reported were impure.

Coassembling Mesoporous Zeolitic Imidazolate Frameworks by Directed Reticular Chemistry.

Conventional microporous zeolitic imidazolate frameworks (ZIFs) face limitations in mass transfer and pore accessibility when dealing with large guest molecules. Here, we describe a technique for the synthesis of mesoporous ZIFs (MesoZIFs) using a strategy we term directed reticular chemistry. MesoZIF-8 was prepared through solvent evaporation-induced coassembly of polystyrene--poly(ethylene oxide) (PS--PEO), ZIF-8 building blocks, and acetic acid (AcOH), followed by amine-facilitated crystallization of ZIF-8 in the interstices of PS--PEO micelles.

Reversible Nucleophilic Ring-Opening of Tetraoxapentacene Derivatives: Accessing New Materials for Thermally Activated Delayed Fluorescence.

We report the unexpected nucleophilic ring-opening reaction of electron deficient dioxins in the presence of carbazole under basic conditions. This nucleophilic ring-opening reaction is reversible under basic conditions in the absence of nucleophiles. Further, we demonstrate that this unexpected reactivity can be used to prepare novel donor-acceptor compounds that are emissive in solution and as thin films and exhibit thermally activated delayed fluorescence (TADF).

The Future is Bright: The Emergence of Glassy Organic Dots for Biological Applications.

Glassy organic dots (g-Odots) are an emerging class of luminescent nanoparticles that offer enhanced photostability, superior brightness, and modular tunability compared to other commonly employed nanoparticles. In the last several years, they have been used as bioimaging probes for single- and multi-photon cellular imaging, exhibiting low cytotoxicity even after several days. While they are emerging as promising materials for use in biological applications, g-Odots face several key challenges before their use can become widespread.

Triplet-Triplet Annihilation Upconversion from Red to Blue Light Using a TADF Sensitizer Based Polymer.

Molecules capable of thermally activated delayed fluorescence (TADF) can exhibit triplet lifetimes on the order of μs-ms as well as low energy losses in the intersystem crossing (ISC) process. As a result, they have great potential to be used as sensitizers in triplet-triplet annihilation upconversion (TTA-UC) systems with high anti-Stokes shifts, replacing traditional phosphorescent sensitizers. In this study, we employ a red-absorbing boron difluoride curcuminoid-based TADF molecule as the sensitizer and a 9,10-diphenylanthracene derivative as the annihilator.

Organelle-Targeting Polymer Dots Exhibiting Thermally Activated Delayed Fluorescence for Subcellular Imaging.

Selective imaging of specific subcellular structures provides valuable information about the cellular microenvironment. Materials exhibiting thermally activated delayed fluorescence (TADF) are rapidly emerging as metal-free probes with long-lived emission for intracellular time-gated imaging applications. Polymers incorporating TADF emitters can self-assemble into luminescent nanoparticles, termed polymer dots (Pdots), and this strategy enables them to circumvent the limitations of commercial organelle trackers and small molecule TADF emitters.

Triplet dynamics reveal loss pathways in multi-resonance thermally activated delayed fluorescence emitters.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials are of interest for light-emitting applications due to their narrow emission bandwidths and high photoluminescence quantum yields. Whilst there have been numerous examples of multi-resonance molecules exhibiting efficient TADF, the photophysics and mechanism of TADF in multi-resonance emitters have not been investigated to the same extent as the more conventional spatially separated donor-acceptor TADF materials, limiting the development of MR-TADF devices. Here we study the photophysics of a multi-resonance TADF material, OQAO(mes), using transient absorption spectroscopy to spectrally resolve the triplet population(s).

Investigating Hydrogen Bonding in Quinoxaline-Based Thermally Activated Delayed Fluorescent Materials.

In recent years, hydrogen bonding (H bonding) as an intramolecular locking strategy has been proposed to enhance photoluminescence, color purity, and photostability in thermally activated delayed fluorescence (TADF) materials. Rigidification as a design strategy is particularly relevant when using electron-deficient -heterocycles as electron acceptors, because these materials often suffer from poor performance as orange to near-infrared emitters as a result of the energy gap law. To critically evaluate the presence of H bonding in such materials, two TADF-active donor-acceptor dyads, ACR-DQ and ACR-PQ, were synthesized.

Polymer Dots with Delayed Fluorescence and Tunable Cellular Uptake for Photodynamic Therapy and Time-Gated Imaging.

By combining bioimaging and photodynamic therapy (PDT), it is possible to treat cancer through a theranostic approach with targeted action for minimum invasiveness and side effects. Thermally activated delayed fluorescence (TADF) probes have gained recent interest in theranostics due to their ability to generate singlet oxygen (O) while providing delayed emission that can be used in time-gated imaging. However, it is still challenging to design systems that simultaneously show (1) high contrast for imaging, (2) low dark toxicity but high phototoxicity and (3) tunable biological uptake.

Dopants Induce Persistent Room Temperature Phosphorescence in Triarylamine Boronate Esters.

Purely organic materials exhibiting room temperature phosphorescence (RTP) are promising candidates for oxygen sensors and information encryption owing to their cost-effective and environmentally friendly nature. Herein, we report a bimolecular RTP system where DTBU acts as the guest and TBBU serves as the host. In contrast to previously reported results, we find that both pure DTBU and TBBU do not exhibit RTP in the solid state even under N atmosphere.

Organic Photothermal Materials Obtained Using Thermally Activated Delayed Fluorescence Design Principles.

Organic small molecules with high photothermal conversion efficiencies that absorb near-infrared light are desirable for photothermal therapy due to their improved biocompatibility compared to inorganic materials and their ability to absorb light in the biological transparency window (650-1350 nm). Here we report three donor-acceptor organic materials DM-ANDI, O-ANDI, and S-ANDI that show high photothermal conversion efficiencies of 46-68 % with near-infrared absorption. The design of these molecules is based on the rational modification of a thermally activated delayed fluorescence material to favour a low photoluminescence quantum yield by reducing HOMO-LUMO overlap.

Semiconducting Polymer Dots Directly Stabilized with Serum Albumin: Preparation, Characterization, and Cellular Immunolabeling.

Semiconducting polymer dots (Pdots) are brightly fluorescent nanoparticles of growing interest for bioanalysis and imaging. A recurring challenge with these materials is obtaining robust physical and colloidal stability and low nonspecific binding. Here, we prepared and characterized Pdots with bovine serum albumin (BSA) as the stabilizing agent (BSA-Pdots) instead of a more conventionally used amphiphilic polymer, both without and with cross-linking of the protein using glutaraldehyde (BSA(GA)-Pdots) or disuccinimidyl glutarate.

Excited-state dynamics of C-symmetric heptazine-based thermally activated delayed-fluorescence emitters.

Heptazine-based materials have recently emerged as a promising motif for thermally activated delayed fluorescence, as their near-zero or negative singlet-triplet energy gaps enable extremely fast reverse intersystem crossing (rISC) rates. Another method for achieving a high rate of rISC is through the use of highly symmetric emitters, which benefit from energy-level degeneracies and a high density of states. Here, we investigate the effect of combining these two design strategies on the excited-state dynamics of C-symmetric emitters containing heptazine cores.

Red-Shifted Emission in Multiple Resonance Thermally Activated Delayed Fluorescent Materials through Malononitrile Incorporation.

Multiple resonance thermally activated delayed fluorescent (MR-TADF) materials offer higher color purity than conventional TADF materials but suffer from aggregation-caused quenching (ACQ) and rarely exhibit red emission. Herein, two malononitrile-substituted emitters are synthesized from a quinolino[3,2,1-]acridine-5,9-dione () MR-TADF precursor. Both materials maintain MR-TADF, while they display red-shifted fluorescence.

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Triplet-triplet energy transfer (EnT) is a powerful activation pathway in photocatalysis that unlocks new organic transformations and improves the sustainability of organic synthesis. Many current examples, however, still rely on platinum-group metal complexes as photosensitizers, with associated high costs and environmental impacts. Photosensitizers that exhibit thermally activated delayed fluorescence (TADF) are attractive fully organic alternatives in EnT photocatalysis.

Achieving White-Light Emission Using Organic Persistent Room Temperature Phosphorescence.

Artificial lighting currently consumes approximately one-fifth of global electricity production. Organic emitters with white persistent RTP have potential for applications in energy-efficient lighting technologies, due to their ability to harvest both singlet and triplet excitons. Compared to heavy metal phosphorescent materials, they have significant advantages in cost, processability, and reduced toxicity.

Dibenzodipyridophenazines with Dendritic Electron Donors Exhibiting Deep-Red Emission and Thermally Activated Delayed Fluorescence.

The development of deep-red thermally activated delayed fluorescence (TADF) emitters is important for applications such as organic light-emitting diodes (OLEDs) and biological imaging. Design strategies for red-shifting emission include synthesizing rigid acceptor cores to limit nonradiative decay and employing strong electron-donating groups. In this work, three novel luminescent donor-acceptor compounds based on the dibenzo[,]dipyrido[3,2-h:20-30-]-phenazine-12-yl () acceptor were prepared using dendritic carbazole-based donors 3,3″,6,6″-tetramethoxy-9'-9,3':6',9″-tercarbazole (), ,,,-tetra--tolyl-9-carbazole-3,6-diamine (), and ,,,-tetrakis(4-methoxyphenyl)-9-carbazole-3,6-diamine ().

Thermally Activated Delayed Fluorescence and Room-Temperature Phosphorescence in Materials with Imidazo-pyrazine-5,6-dicarbonitrile Acceptors.

Three donor-acceptor compounds based on the imidazo-pyrazine-5,6-dicarbonitrile (IPDC) acceptor were synthesized. The IPDC emitters exhibit blue to near-infrared (NIR) emission with up to 54 % photoluminescent quantum yield. 9,9-Dimethyl-9,10-dihydroacridine (ACR), phenoxazine (POX), and phenothiazine (PTZ) served as electron donors.

Uncovering the Mechanism of Thermally Activated Delayed Fluorescence in Coplanar Emitters Using Potential Energy Surface Analysis.

Planarized emitters exhibiting thermally activated delayed fluorescence (TADF) have attracted attention due to their narrow emission spectra, improved photostability, and high quantum yields, but with large singlet-triplet energy gaps (Δ) and no heavy atoms, the origin of their TADF remains a subject of debate. Here we prepare two isomeric, coplanar donor-acceptor compounds, with performing dual TADF and room-temperature phosphorescence but with exhibiting only prompt fluorescence. Although conventional TADF design principles suggest that neither isomer should exhibit TADF, we reveal differences in the excited state potential energy surfaces that enable spin-flip processes in only one isomer.

Mechanistic Principles for Engineering Hierarchical Porous Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) have generated tremendous research interest in the past two decades, due to their high surface areas, tailorable active sites, and tunable structures. Hierarchical porous MOFs (HP-MOFs) with two or more pore systems are particularly attractive, benefiting from improved active site accessibility and enhanced mass diffusivity in applications involving bulk molecules. This review outlines the mechanistic principles used for the rational design of HP-MOFs, current techniques used to measure their hierarchical porosities, as well as their emerging applications.

Polymer dots and glassy organic dots using dibenzodipyridophenazine dyes as water-dispersible TADF probes for cellular imaging.

Fluorescence imaging of living cells is key to better understanding cellular morphology and biological processes. Water-dispersible nanoparticles exhibiting thermally activated delayed fluorescence (TADF) have recently emerged as useful probes for time-resolved fluorescence imaging (TRFI), circumventing interference from biological autofluorescence. Many existing approaches, however, require TADF dyes with specific structural features, precluding many high-performance TADF materials from being used in this application.

An imidazoacridine-based TADF material as an effective organic photosensitizer for visible-light-promoted [2 + 2] cycloaddition.

Energy transfer (EnT) is a fundamental activation process in visible-light-promoted photocycloaddition reactions. This work describes the performance of imidazoacridine-based TADF materials for visible-light mediated triplet-triplet EnT photocatalysis. The TADF material ACR-IMAC has been discovered as an inexpensive, high-performance organic alternative to the commonly used metal-based photosensitizers for visible-light EnT photocatalysis.

Luminescent Surface-Tethered Polymer Brush Materials.

Surface-tethered polymers are unique molecular architectures that have been recently used in advanced sensors, electronics and biomedical applications. However, techniques for characterizing these materials in their surface-tethered form remain limited. The incorporation of luminescent functionality into these materials has enabled new characterization methods, while also unlocking new applications in optoelectronics, stenography and sensing.