Fluorescence lifetime imaging microscopy (FLIM) is an optical imaging modality that can provide multiplexed readouts with remarkable sensitivity to cellular microenvironments. Even though fluorescence lifetimes can distinguish fluorophores having overlapping spectral profiles, conventional fluorophores possess a narrow range of emission lifetimes (typically shorter than 5 ns) that limits their potential for multiplexed imaging. In this work, we have systematically designed and evaluated a combination of thermally activated delayed fluorescence (TADF) nanoprobes for multiplexed FLIM. We have synthesized a collection of 36 TADF biocompatible nanoprobes with long and diverse fluorescence lifetimes in aqueous media (up to 15 ns) and employed selected probes for live-cell imaging of bacterial cells under physiological conditions. By leveraging the exceptionally broad range of fluorescence lifetimes of these TADF emitters, we have achieved unprecedented simultaneous imaging of five nanoprobes within a single spectral window using a FLIM-phasor strategy. These findings demonstrate that TADF emitters are excellent scaffolds to unlock the capabilities of fluorescence lifetime imaging for multi-color biological studies.

The relatively slow reverse intersystem cross rate constant ( k RISC ) of multi-resonant thermally activated delayed fluorescence (MR-TADF) emitters has been recognized as perhaps the most critical factor governing their rather significant efficiency roll-off in organic light-emitting diodes (OLEDs). A recent study identified a figure of merit for TADF materials, which captures the relevant exciton dynamics processes and correlates these with efficiency roll-off in the resulting device. Two MR-TADF emitters tBTCzBN and tSeCzBN, containing, respectively, dibenzothiophenocarbazole and dibenzoselenophenocarbazoles were designed. Their rigid p-and n-doped nanographene structures, incorporating heavy chalcogen atoms at optimal locations, result in fast 𝑘 γ S s of 1.7×10 8 and 7.7 ×10 7 s -1 , k RISC values of 2.6 ×10 5 and 3.9 ×10 6 s -1 , and FOMs of 1.8 ×10 5 and 3.9 ×10 5 s -1 for tBTCzBN and tSeCzBN, respectively. The sensitizer-free OLEDs with tBTCzBN and tSeCzBN exhibited green electroluminescence [CIE coordinates of (0.14, 0.61), and (0.18, 0.61)]. Notably, the device with tSeCzBN delivered superior high maximum external quantum efficiencies (EQE max ) of 37.1%, with EQE 1000 of 31.7%, which is one of the highest reported EQE1000 values, and is matched by a remarkably low efficiency roll-off of 14%, especially compared to other MR-TADF OLEDs. Moreover, the incorporated chalcogen atoms modulate the frontier molecular orbital levels of the emitter, resulting in much-improved operational stability as a result of suppressed hole trapping. This work highlights the distinct benefits and the importance of judicious incorporation of heavy atoms within MR-TADF emitter structures to facilitate efficient exciton harvesting and enhance device performance.

Clinical drug delivery requires precise control, yet conventional methods suffer from fluctuating concentrations and low bioavailability. While implantable devices are promising for long-term therapy, wireless dosage control remains challenging. We report an implantable acoustofluidic chip for on-demand drug delivery. Fabricated via soft lithography and two-photon polymerization, the device integrates a drug-loaded hydrogel and a sharp-edge microcantilever array within a polydimethylsiloxane microchannel. Wireless ultrasound actuation induces acoustic streaming via the microcantilever array, generating a net pumping flow to drive drug release. In addition, the device also enables liquid-phase medications to be controllably released when the drug-loaded hydrogel is replaced by a liquid-phase formulation. Biocompatibility evaluation over a 144 h cell co-culture period confirms negligible cytotoxicity of the acoustofluidic chip. This work demonstrates a promising strategy for wireless, programmable implantable drug delivery.

Die Fluoreszenzlebensdauer‐Mikroskopie (FLIM) ist ein optisches Bildgebungsverfahren, das multiplexe Messwerte mit bemerkenswerter Empfindlichkeit für zelluläre Mikroumgebungen liefern kann. Obwohl mittels Fluoreszenzlebensdauern Fluorophore mit überlappenden Spektralprofilen unterschieden werden können, besitzen herkömmliche Fluorophore einen engen Bereich an Emissionslebensdauern (typischerweise kürzer als 5 ns), was ihr Potenzial für die multiplexe Bildgebung einschränkt. In dieser Arbeit haben wir systematisch eine Kombination aus thermisch aktivierten verzögerten Fluoreszenz‐Nanoproben (TADF) für die multiplexe FLIM entwickelt und evaluiert. Wir haben eine Bibliothek von 36 biokompatiblen TADF‐Nanoproben mit langen und unterschiedlichen Fluoreszenzlebensdauern in wässrigen Medien (bis zu 15 ns) synthetisiert und ausgewählte Sonden zur Live‐Zell‐Bildgebung von Bakterien unter physiologischen Bedingungen eingesetzt. Durch die Nutzung des außergewöhnlich breiten Spektrums an Fluoreszenzlebensdauern dieser TADF‐Emitter haben wir mithilfe einer FLIM‐Phasor‐Strategie eine beispiellose simultane Bildgebung von fünf Nanoproben innerhalb eines einzigen Spektralfensters erreicht. Diese Ergebnisse zeigen, dass TADF‐Emitter hervorragende Gerüste sind, um die Möglichkeiten der Bildgebung der Fluoreszenzlebensdauer für mehrfarbige biologische Studien zu erschließen.

Multi-resonant thermally activated delayed fluorescence (MR-TADF) emitters offer an attractive solution for the fabrication of colour-saturated organic light-emitting diodes (OLEDs). Still, their rigid frameworks often lead to slow reverse intersystem crossing and aggregation-caused quenching. To address these challenges and simultaneously introduce chiroptical properties in solution-processable materials, here we present the first examples of chiral intramolecular Förster resonance energy transfer (FRET) MR-TADF dendrimers, CzPBN-CzBN and CzPBA-CzBN . These emitters combine an MRTADF core with chiral paracyclophane (CzP)-based donor dendrons linked to different acceptor units, benzonitrile for CzPBN-CzBN and benzoic acid for CzPBA-CzBN . While both dendrimers show narrowband TADF emission, the nature of the acceptor impacts their chiroptical properties. Specifically, CzPBA-CzBN exhibits circularly polarised luminescence (CPL), whereas CzPBN-CzBN does not due to a weaker circular dichroism signal. Conversely, in solution-processed hyperfluorescent (HF) OLEDs, the device with CzPBN-CzBN achieved a superior maximum external quantum efficiency ( EQE max ) of 19.7% and lower efficiency roll-off ( EQE of 18.9% at 1000 cd m -2 ) compared to the device with CzPBA-CzBN ( EQE max/1000 = 17.2/16.5%). These findings reveal an intrinsic trade-off between CPL response and HF device performance, demonstrating how precise modulation of the excited-state manifold via acceptor engineering can be used to tailor the properties of intramolecular sensitised TADF emitters.

Efficient, ultrapure green organic light-emitting diodes (OLEDs) fabricated via wet processing are crucial for ultrahigh definition displays but remain highly challenging due to the paucity of suitable emitters. Herein, we developed Oly-BN, a novel multipleresonance thermally activated delayed fluorescence (MR-TADF) emitter featuring a distinct Olympic-patterned boron-distribution. The zigzag doped heteroatom polycyclic aromatic framework enables near-degenerate singlet/triplet excited states. Integrating para-N-π-B motifs helps regulate the triplet manifold and emission color point, enabling energetically accessible higher lying triplet excited states with enhanced spinorbit coupling, while also suppressing low-frequency structural relaxation and modulating the optical bandgap. Oly-BN in toluene exhibits vivid green emission at 522 nm with a narrow full width at half maximum (FWHM) of 17 nm, a photoluminescence quantum yield of 95%, and a fast reverse intersystem crossing rate constant of 6.9×106 s−1. Additionally, its highly twisted conformation weakens intermolecular interactions and favors bright, solid-state emission. The nonsensitized solution-processed OLEDs deliver ultrapure green electroluminescence with a CIEy value up to 0.73, and achieves an optimized maximum external quantum efficiency of 39.4%, which remains high at 29.9% at 1000 cd m-2. This work not only provides a promising highly saturated green emitter for solution-processed OLEDs but also demonstrates the importance of precisely integrating heteroatoms in modulating photophysical properties of MR-TADF emitters.

Nitrogen/carbonyl (N/C═O) based multi‐resonant thermally activated delayed fluorescence (MR‐TADF) emitters are attractive due to their bright, narrowband emission and the ease with which they can be synthesized. However, their photophysics typically suffer from slow reverse intersystem crossing (RISC) because of their relatively large singlet‐triplet energy gap (Δ E ST ). Thus, the organic light‐emitting diodes (OLEDs) with these emitters typically show severe efficiency roll‐off. Here, two MR‐TADF emitters DiKTaSe and tBuCz‐DiKTaSe have been designed and synthesized. The introduction of selenium in the form of an annelated benzoselenophene enhances spin‐orbit coupling and increases the RISC rate. The twisted ortho ‐substituted tert ‐butylcarbazole moiety in tBuCz‐DiKTaSe helps to suppress aggregation‐caused quenching of the emission in films. In addition, the large size of the selenium atom and long C─Se bonds induce helical chirality in both DiKTaSe and tBuCz‐DiKTaSe . Finally, the OLEDs with DiKTaSe showed maximum external quantum efficiency (EQE max ) of 22.7% while OLEDs with tBuCz‐DiKTaSe showed a higher EQE max of 27.8% and less‐pronounced efficiency roll‐off, with EQE at 100 cd m −2 (EQE 100 )/ EQE at 1000 cd m −2 (EQE 1000 ) of 23.5/12.5%. These efficiency values are amongst the highest of devices employing DiKTa‐based emitters. Our work provides key insight into how to judiciously employ heavy atoms to increase the performance of the emitter and the device.

This study explores the impact of the regioisomerism of a heavy chalcogen atom on the photophysical properties of multi-resonant thermally activated delayed fluorescence (MR-TADF) materials. We synthesized two pairs of isomeric MR-TADF emitters containing different benzothienocarbazole moieties, tDPABT1B/tDPABT2B and tCzBT1B/tCzBT2B. Theoretical calculations indicate that tDPABT2B and tCzBT2B possess higher spin-orbital coupling values (0.27 and 0.60 cm⁻¹) compared to their respective isomers. The photophysical study reveals that tDPABT2B and tCzBT2B have twofold faster reverse intersystem crossing rate constants of 0.5 × 10⁵ and 2.7 × 10⁵ s⁻¹, respectively, than their isomeric counterparts. The sensitizer-free organic light-emitting diodes (OLEDs) with tCzBT1B and tCzBT2B exhibited green emissions [CIE coordinates of (0.12, 0.54)] and showed high maximum external quantum efficiencies (EQEmax) of 34.9% and 34.3%, respectively. Notably, the device with tCzBT2B demonstrated a reduced efficiency roll-off (34% decrease at 1000 cd cm⁻²) compared to that with tCzBT1B (48% decrease at 1000 cd cm⁻²), highlighting the distinct benefits and importance of the regiochemistry of the heavy atom in contributing to an enhancing device performance.

Multiresonant thermally activated delayed fluorescence (MR-TADF) compounds exhibit significant potential as emitters in organic light-emitting diodes (OLEDs) due to their bright, narrowband emission, which provides a solution to the color saturation required by industry for ultra-high definition (UHD) displays. Here, we report the smallest three boron doped MR-TADF emitter (TBDON), a design that fuses two boron-contacting MR-TADF emitters, DOBNA and ADBNA-Me-Mes, together. The resulting emitter, TBDON, shows desirable narrowband pure blue emission (λ PL = 472 nm with FWHM = 28 nm) and efficient TADF with efficient reverse intersystem crossing (RISC), supported by a relatively fast k RISC of 7.8 × 104 s-1. The OLED with TBDON showed a high maximum external quantum efficiency (EQEmax) of 24.4%, an EQE of 17.2% at 100 cd m-2, and Commission Internationale de l'Éclairage (CIE) coordinates of (0.14, 0.16). The ternary device employing DMAC-DPS as an assistant dopant showed improved performance with a higher EQEmax of 28.1% and milder efficiency roll-off with an EQE100/1000 of 24.4/17.5%. The high device performance demonstrates the promise of the proposed molecular design.

The development of circularly polarized multiresonant thermally activated delayed fluorescence materials with fast reverse intersystem crossing (RISC) process remains a challenge. Herein, we introduce high-lying excited states to assist the RISC process. Through arranging two known MR-TADF emitters tCzBN and DiKTa at the pseudo-ortho position of a chiral skeleton paracyclophane (PCP), the excitedstate density was increased. The proof-of-concept emitter po-PCP-tCzBN-DiKTa shows nearly three times higher kRISC (5.31 x 104 s-1) than PCP-tCzBN (1.73 x 104 s-1) without compromising color purity and exhibiting circularly polarized luminescence with |gPL| values at the 10-4 level. The solution-processed organic light-emitting diodes with po-PCP-tCzBN-DiKTa show high maximum external quantum efficiency (EQEmax) reaching 23% with a moderate efficiency roll-off, showing EQE of 18% and 9% at 100 and 1000 cd/m2.

The development of narrowband emissive, bright, and stable solution-processed organic light-emitting diodes (SP-OLEDs) remains a challenge. Here, we present a strategy that merges within a single emitter a TADF sensitizer responsible for exciton harvesting and a MR-TADF motif that provides bright and narrowband emission. This emitter design also shows strong resistance to aggregate formation and aggregation-cause quenching. It is based on a known MR-TADF emitter DtBuCzB with a donor-acceptor TADF moiety consisting of either tert-butylcarbazole donors (tBuCzCO2HDCzB) or second-generation carbazole-based donor dendrons (2GtBuCzCO2HDCzB) and a benzoate acceptor. The TADF moiety acts as an exciton harvesting antenna and transfer these excitons via Förster resonance energy transfer to the MR-TADF emissive core. The SP-OLEDs with 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB thus showed very high maximum external quantum efficiencies (EQEmax of 27.9 and 22.0%) and minimal efficiency roll-off out to 5000 cd m-2.

Ultrasound-actuated microrobots that incorporate entrapped microbubbles rely on acoustic streaming thrust for propulsion. While bubble size and resonance have been extensively studied, the role of opening size remains less understood. In this study, we numerically investigate how the opening size affects both streaming flow and the resulting thrust. Finite element analysis (FEA) reveals that although streaming velocity increases with oscillation amplitude and opening size, the generated thrust does not always scale proportionally. Counterintuitively, microbubbles with larger openings are more likely to produce greater thrust than those with smaller openings under identical acoustic excitation, despite generating weaker streaming flows. This phenomenon is experimentally confirmed using a microcantilever-based thrust measurement system. Our study provides key insights into the mechanics of microbubble-driven propulsion and highlight the the critical role of opening size in acoustic streaming thrust, offering valuable guidance for the design of next-generation microbubble-based acoustic microrobots for various biomedical applications.

Strategies that produce OLEDs that simultaneously achieve outstanding electroluminescence efficiency, small efficiency roll‐off, good stability, and high color purity remain in strong demand. Herein, we report how judicious decoration of a benzochalcogenophene onto the BCzBN core leads to an acceleration of reverse intersystem crossing ( k RISC ) without sacrificing either color fidelity and photoluminescence quantum yield ( Φ PL ). Compared with BCzBN , the k RISC of BN‐S and BN‐Se are accelerated to 2.5 × 10 5 and 7.2 × 10 5 s −1 from 1.4 × 10 4 s −1 , each with near‐unity Φ PL s. BN‐S and BN‐Se show narrowband emission at 483 nm (FWHM of 22 nm) and 485 nm (FWHM of 22 nm). The corresponding non‐sensitized OLEDs using BN‐S and BN‐Se exhibited record‐breaking maximum external quantum efficiency (EQE max ) of 43.1 and 36.9%, without any external light extraction techniques. Furthermore, the BN‐Se ‐based OLED showed ultralow efficiency roll‐off, with EQEs remaining at 36.7 and 31.8% at 100 and 1000 cd m −2 , respectively. These emitters do not easily suffer from aggregation‐caused quenching. Even at 12 wt% doping, the EQE max of the OLEDs with BN‐S and BN‐Se were 36.7 and 36.4%, respectively, with mild efficiency roll‐off (EQEs at 1000 cd m −2 of 19.1 and 30.8%, respectively), and nearly unchanged electroluminescence spectra.

Multi-resonant TADF materials are a promising class of emitters capable of addressing the BT.2020 industry requirement for blue emission in electroluminescent displays as they simultaneously show narrowband emission and can harvest both singlet and triplet excitons to produce light. However, these emitters are typically planar and prone to aggregation and their moderately large singlet-triplet energy gap (Delta EST) leads to slow upconversion kinetics resulting in severe efficiency roll-off in the device. In this study we present a molecular design that simultaneously results in an emitter having a faster reverse intersystem crossing rate constant (kRISC) and suppressed aggregation in the film state. Mes-tDABNA emits at lambda PL of 465 nm as 4 wt% doped films in SF3-RZ and has a short delayed lifetime of 45.2 mu s. Vacuum-deposited OLEDs with Mes-tDABNA showed blue emission at CIE coordinates of (0.13, 0.15) and a maximum external quantum efficiency, EQEmax, of 18.4%. Unsurprisingly, these devices suffered from rather strong efficiency roll-off (EQE1000 of 5.6%). With the aim of addressing this efficiency roll-off, hyperfluorescent devices containing DMAC-DPS as a TADF sensitizer were fabricated, which showed an improved EQEmax of 23.1% at CIE coordinates of (0.13, 0.17) and milder efficiency roll-off (EQE1000 of 12.7%). These devices showed one of the highest EQE1000 based on DABNA-based emitters to date.

Here the utility and potential of an emitter design are demonstrated, consisting of a narrowband-emitting multiresonant thermally activated delayed fluorescent (MR-TADF) core that is decorated with a suitably higher energy donor-acceptor TADF moiety. Not only does this D-A TADF group offer additional channels for triplet exciton harvesting and confers faster reverse intersystem crossing (RISC) kinetics but it also acts as a steric shield, insulating the emissive MR-TADF core from aggregation-caused quenching. Two emitters, DtCzBN-CNBT1 and DtCzBN-CNBT2, demonstrate enhanced photophysical properties leading to outstanding performance of the organic light-emitting diodes (OLEDs). DtCzBN-CNBT2, containing a D-A TADF moiety, has a faster kRISC (1.1 × 105 s-1) and higher photoluminescence quantum yield (ΦPL: 97%) compared to DtCzBN-CNBT1 (0.2 × 105 s-1, ΦPL: 90%), which contains a D-A moiety that itself is not TADF. The sensitizer-free OLEDs with DtCzBN-CNBT2 achieve a record-high maximum external quantum efficiency (EQEmax) of 40.2% and showed milder efficiency roll-off (EQE1000 of 20.7%) compared to the DtCzBN-CNBT1-based devices (EQEmax of 37.1% and EQE1000 of 11.9%).

Chiral multiresonant thermally activated delayed fluorescence (MR-TADF) materials show great potential as emitters in circularly polarized (CP) organic light-emitting diodes (CP-OLEDs) owing to their bright and narrowband CP emission. Here, two new chiral MR-TADF emitters tBuPh-BN and DPA-tBuPh-BN possessing intrinsically helical chirality have been synthesized and studied. The large steric interactions between the tert-butylphenyl groups not only induce the helical chirality but also provide a notable configurational stability to the enantiomers. Racemic mixtures of tBuPh-BN and DPA-tBuPh-BN show narrowband emission at 490 and 477 nm with full-width at half maximum (FWHM) of 25 and 28 nm and photoluminescence quantum yields, PL, of 85 and 54% in toluene. The separated enantiomers of tBuPh-BN and DPA-tBuPh-BN show symmetric circularly polarized luminescence (CPL) with respective dissymmetry factors |gPL| values of 1.5×10-3 and 0.9×10-3. The hyperfluorescence organic light-emitting diodes (HF-OLEDs) with tBuPh-BN and DPA-tBuPh-BN acting as terminal emitters and 2,3,4,5,6-penta-(9H-carbazol-9-yl)benzonitrile (5CzBN) as their assistant dopant exhibited, respectively, maximum external quantum efficiencies (EQEmax) of 20.9 and 15.9% at 492 and 480 nm with FWHM of 34 and 38 nm. This work demonstrates a strategy for developing intrinsically helically chiral MR-TADF emitters possessing significant configurationally stability, which can be used in HF-OLEDs.

In this study, we explore the impact of halogen functionalization on the photophysical properties of the commonly used organic light-emitting diode (OLED) host material, 1,3-bis(N-carbazolyl)benzene (mCP). Derivatives with different numbers and types of halogen substituents on mCP were synthesized. By measuring steady-state and transient photoluminescence at 6 K, we study the impact of the type, number, and position of the halogens on the intersystem crossing and phosphorescence rates of the compounds. In particular, the functionalization of mCP with 5 bromine atoms results in a significant increase of the intersystem crossing rate by a factor of 300 to a value of (1.5 +/- 0.1) x 10(10) s(-1), and the phosphorescence rate increases by 2 orders of magnitude. We find that the singlet radiative decay rate is not significantly modified in any of the studied compounds. In the second part of the paper, we describe the influence of these compounds on the reverse intersystem crossing of the 7,10-bis(4-(diphenylamino)phenyl)-2,3-dicyanopyrazino-phenanthrene (TPA-DCPP), a TADF guest, via the external heavy atom effect. Their use results in an increase of the reverse intersystem crossing (RISC) rate from (8.1 +/- 0.8) x 10(3) s(-1) for mCP to (2.7 +/- 0.1) x 10(4) s(-1) for mCP with 5 bromine atoms. The effect is even more pronounced for the mCP analogue containing a single iodine atom, which gives a RISC rate of (3.3 +/- 0.1) x 10(4) s(-1). Time-dependent DFT calculations reveal the importance of the use of long-range corrected functionals to predict the effect of halogenation on the optical properties of the mCP, and the relativistic approximation (ZORA) is used to provide insight into the strength of the spin-orbit coupling matrix element between the lowest-lying excited singlet and triplet states in the different mCP compounds.

Thermally activated delayed fluorescence (TADF) materials are expected to address triplet-related losses in electrically driven organic lasers, as the electrically generated triplets in the materials can be converted to radiative singlets through reverse intersystem crossing (RISC). This offers a way to bypass triplet absorption and annihilation in organic semiconductor lasers (OSLs). In this work we present two versatile TADF emitters 4tCzPz and 4αCbPz for application in OLEDs and OSLs. Both emitters possess moderately high ΔEST (~0.30 eV) and show high ΦPL in solution and solid state and prominent stimulated emission features in solution. Films of 4tCzPz and 4αCbPz doped in mCBP show an amplified spontaneous emission (ASE) threshold of 41.0 and 44.9 µJ/cm2, respectively. The OLEDs with 4tCzPz and 4αCbPz emitted with peak wavelengths of 492 nm and 475 nm, respectively, and showed corresponding maximum external quantum efficiencies, EQEmax, of 24.6 and 21.3%. Our research shows that D-A TADF materials hold significant potential not only as emitters for OLEDs but also in OSLs.