Nm In Toluene Research Articles

Synthesis and Structural Characterization of Carbazole‐Tailored Luminescent Triarylmethyl Radical and its Stable Cation

AbstractThe development of novel luminescent radicals, characterized by their unique doublet emission, endows a significant challenge. In this study, we reported the synthesis of a luminescent neutral radical, BCzAnM‐R, tailored by two carbazolyl groups and an anthryl group to achieve a nonalternant structure. It exhibited near‐infrared emission with a peak at 1020 nm in toluene. Interestingly, its corresponding cation, BCzAnM‐C, was synthesized through an unconventional SnCl2‐mediated reduction‐aromatization‐oxidation reaction in one‐pot and gram‐scale. The cation demonstrated remarkable stability for up to weeks in ambient conditions and facilitated the silica‐gel chromatography isolation as an organic salt with SnCl3− as the counter ion. The carbazolyl groups effectively modulate molecular structures, photophysical properties, and stabilities. Notably, BCzAnM‐R represents the first luminescent triarylmethyl radical with two carbazolyl groups directly attached to the central carbon.

Ultra-Narrowband Circularly Polarized Luminescence from Multiple 1,4-Azaborine-Embedded Helical Nanographenes.

In this manuscript we present a strategy to achieve ultranarrowband circularly polarized luminescence (CPL) from multiple 1,4-azaborine-embedded helical nanographenes. The impact of number and position of boron and nitrogen atoms in the rigid core of the molecule on optical properties─including absorption and emission maxima, photoluminescence quantum yield, Stokes shift, excited singlet-triplet energy gap and full width at half-maximum (fwhm) for CPL and fluorescence─was investigated. The molecules reported here exhibits ultranarrowband fluorescence (fwhm 16-17.5 nm in toluene) and CPL (fwhm 18-19 nm in toluene). To the best of our knowledge, this is among the narrowest CPL for any organic molecule reported to date. Quantum chemical calculations, including computed CPL spectra involving vibronic contributions, provide valuable insights for future molecular design aimed at achieving narrowband CPL.

Synthesis and Structural Characterization of Carbazole-Tailored Luminescent Triarylmethyl Radical and its Stable Cation.

The development of novel luminescent radicals, characterized by their unique doublet emission, endows a significant challenge. In this study, we reported the synthesis of a luminescent neutral radical, BCzAnM-R, tailored by two carbazolyl groups and an anthryl group to achieve a nonalternant structure. It exhibited near-infrared emission with a peak at 1020 nm in toluene. Interestingly, its corresponding cation, BCzAnM-C, was synthesized through an unconventional SnCl2-mediated reduction-aromatization-oxidation reaction in one-pot and gram-scale. The cation demonstrated remarkable stability for up to weeks in ambient conditions and facilitated the silica-gel chromatography isolation as an organic salt with SnCl3-as the counter ion. The carbazolyl groups effectively modulate molecular structures, photophysical properties, and stabilities. Notably, BCzAnM-R represents the first luminescent triarylmethyl radical with two carbazolyl groups directly attached to the central carbon.

Multi-resonance thermally activated delayed fluorescence polymers for high-efficiency and narrowband solution-processed green OLEDs.

A series of green multi-resonance thermally activated delayed fluorescence polymeric emitters featuring conjugation-interrupted main chains were facilely prepared via metal-free superacid-catalyzed Friedel-Crafts polyhydroxyalkylation. These emitters exhibited photoluminescence quantum yields of up to 76% and small full-widths at half maximum of 35-38 nm in toluene. The corresponding solution-processed OLEDs achieved an excellent maximum external quantum efficiency of 19.4%, with CIE coordinates of (0.20, 0.62).

Efficient Blue Carbonyl‐Nitrogen Multi‐Resonance Molecules for High‐Performance Hyperfluorescence OLEDs

AbstractEfficient blue multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials are highly desired for the fabrication of organic light‐emitting diodes (OLEDs) with high color purity. But only very limited carbonyl‐nitrogen (CO‐N) blue MR‐TADF are well‐developed. Herein, two new blue CO‐N MR‐TADF molecules (tBuPQCZ and 2tBuPQCZ) are explored by introducing bulky substituents to a planar CO‐N MR‐TADF core constructed by fusing carbonyl groups with carbazole, and their thermal stability, electronic structures, and photophysical properties are investigated. They exhibit blue photoluminescence (PL) peaks at 451 and 447 nm, and narrow full width at half maximums (FWHMs) of 26 and 25 nm in toluene. In doped films, they exhibit strong blue emissions with PL peaks at 474 and 469 nm, FWHMs of 51 and 49 nm, and satisfactory PL quantum yields of 80% and 72%. Moreover, blue OLEDs using them as emitters exhibit excellent external quantum efficiencies (EQEs) of 20.4% and 21.5%, and the hyperfluorescence OLEDs based on them provide state‐of‐the‐art EQEs of 30.1% and 29.0% with small FWHMs of 34 and 32 nm and Commission Internationale de I'Eclairage coordinates of (0.136, 0.134) and (0.141, 0.105). The insights gained in this work should be valuble for the development of efficient blue CO‐N MR‐TADF materials.

Near-IR-Absorbing Bis-Donor Functionalized Aza-BODIPY Derivatives: Synthesis and Photophysical Study by Using Transient Optical Spectroscopy.

A series of near-IR absorbing 2,6-diarylated BF2-chelated aza-boron-dipyrromethenes (aza-BDPs) derivatives bearing different electron donors (benzene, naphthalene, phenanthrene, phenothiazine and carbazole) were designed and synthesized. The effect of different electron donor substitutions on the photophysical properties was studied by steady-state UV-vis absorption and fluorescence spectra, electrochemical, time-resolved nanosecond transient absorption (ns-TA) spectroscopy and theoretical computations. The UV-vis absorption spectra of AzaBDP-PTZ and AzaBDP-CAR (λabs=710 nm in toluene) showed a bathochromic absorption profile compared with the reference AzaBDP-Ph (λabs=685 nm in toluene), indicating the non-negligible electronic interaction at the ground state between donor and acceptor moieties. Moreover, the fluorescence is almost completely quenched for AzaBDP-PTZ/AzaBDP-CAR (fluorescence quantum yield, ΦF=0.2-0.7 % in toluene) as compared with the AzaBDP-Ph (ΦF=27 % in toluene). However, the apparent intersystem crossing ability of these compounds is poor, based on the singlet oxygen quantum yield (ΦΔ=0.3-1.5 %). The ns-TA spectral study showed typical Bodipy localized triplet state transient features, short-lived excited triplet state for AzaBDP-Ph (τT=53.2 μs) versus significantly long-lived triplet state for AzaBDP-CAR (τT=114 μs) was observed under deaerated experimental conditions. These triplet state lifetimes are much longer than that obtained with diiodoAzaBDP (intramolecular heavy atom effect, τT=1.5~7.2 μs). These information are useful for molecular structure design of triplet photosensitizers, for which longer triplet state lifetimes are usually desired. Theoretical computations displayed that the triplet state is mainly localized on the AzaBDP core, moreover, it was found that the HOMO/LUMO energy gap decreased after introducing donor moieties to the skeleton as compared with the reference.

High Singlet Oxygen Generating Benzothienyl‐[b]‐fused BODIPY Nanoaggregates and Photoinduced Apoptosis in Human Carcinoma

AbstractHeavy atom free organic materials absorbing in red to near infrared (NIR) region are potential candidates as photosensitizers (PS) in photodynamic therapy (PDT). PDT relies on many factors and one of them is singlet oxygen generation ability of PS in aqueous medium. In this contribution, we report the synthesis of a new PS i. e., 8‐thienyl bisbenzothieno‐[b]‐fused‐boron‐dipyrromethene (BT‐[b]‐fused BODIPY). This PS shows absorption (λabs) at ~650 nm in toluene while in its water‐dispersible nanoaggregates it is found at ~764 nm. Nanoaggregates of BT‐[b]‐fused BODIPY demonstrated dual advantages, (i) facilitating PS release in the cellular system and (ii) sharply enhanced singlet oxygen efficiency ( ~48 %) in aqueous medium. Intracellular reactive oxygen species (ROS) generation was confirmed by 2′,7′‐dichlorodihydrofluorescein diacetate (DCFDA) assay in A549 cells. In vitro photocytotoxic studies of BT‐[b]‐fused BODIPY are carried out in different carcinomas i. e., MCF‐7 and A549 cells. It has zero dark cell toxicity while half maximal inhibitory concentration (IC50) in MCF‐7 is found to be low (6.08±1.1) μM and 7.41±1.9 μM in A549 on 15 min light exposure. These nanoaggregates induce apoptosis in cancer cells on light irradiation thereby proving it to be a potential PS for PDT.

Boron-, sulfur- and nitrogen-doped decacyclic multiple resonance emitters for narrowband deep blue electroluminescence

Two boron-, sulfur- and nitrogen-doped polycyclic aromatic hydrocarbon (PAH) multiple resonance (MR) emitters, namely mDBNS and mDBNStBu, are developed by introducing two pairs of boron (B) and sulfur (S) atoms at meta-positions of central benzene and one carbazole moiety in decacyclic aromatic skeletons. The resultant emitters exhibit efficient deep blue narrowband emission at 451–457 nm with full width at half maximum (FWHM) of 18–22 nm in toluene, together with PLQY of 70%–76% and reverse intersystem crossing rate (kRISC) of 1.1–1.2 × 105 s−1. Solution-processed organic light-emitting diodes (OLEDs) employing mDBNStBu as emitters exhibit deep blue electroluminescence at 462 nm with CIE coordinates of (0.13, 0.12), together with a maximum external quantum efficiency (EQEmax) of 10.4%.

Multi‐Responsive Thermally Activated Delayed Fluorescence Materials: Optical ZnCl2 Sensors and Efficient Green to Deep‐Red OLEDs

AbstractThermally activated delayed fluorescence (TADF) is an emission mechanism whereby both singlet and triplet excitons can be harvested to produce light. Significant attention is devoted to developing TADF materials for organic light‐emitting diodes (OLEDs), while their use in other organic electronics applications such as sensors, has lagged. A family of TADF emitters, TPAPyAP, TPAPyBP, and TPAPyBPN containing a triphenylamine (TPA) donor and differing nitrogen‐containing heterocyclic pyrazine‐based acceptors is developed and systematically studied. Depending on the acceptor strength, these three compounds emit with photoluminescence maxima (λPL), of 516, 550, and 575 nm in toluene. Notably, all three compounds show a strong and selective spectral response to the presence of ZnCl2, making them the first optical TADF sensors for this analyte. It is demonstrated that these three emitters can be used in vacuum‐deposited OLEDs, which show moderate efficiencies. Of note, the device with TPAPyBPN in 2,8‐bis(diphenyl‐phoshporyl)‐dibenzo[b,d]thiophene (PPT) host emits at 657 nm and shows a maximum external quantum efficiency (EQEmax) of 12.5%. This electroluminescence is significantly red‐shifted yet shows comparable efficiency compared to a device fabricated in 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (CBP) host (λEL = 596 nm, EQEmax = 13.6%).

Multiple-resonance thermally activated delayed fluorescence materials based on phosphorus central chirality for efficient circularly polarized electroluminescence.

Circularly polarized organic light-emitting diodes (CP-OLEDs) hold great potential for naked-eye 3D displays, necessitating efficient chiral luminescent materials with an optimal CP luminescence (CPL) dissymmetry factor (g). Herein, we present the first chiral multiple resonance thermally activated delayed fluorescence (MR-TADF) materials containing a phosphorus chiral center by incorporating 5-phenylbenzo[b]phosphindole-5-oxide into the para-position of two MR-TADF cores. The compounds, NBOPO and NBNPO, exhibit photoluminescence peaks at 462 and 498 nm with narrow full-width at half-maximum values of 25 and 24 nm in toluene, respectively. Notably, (R/S)-NBOPO and (R/S)-NBNPO enantiomers display high quantum yields of 87% and 93% and symmetric CPL with |gPL| factors of 1.18 × 10-3 and 4.30 × 10-3, respectively, in doped films. Moreover, the corresponding CP-OLEDs show impressive external quantum efficiencies of 16.4% and 28.3%, along with symmetric CP electroluminescence spectra with |gEL| values of 7.0 × 10-4 and 1.4 × 10-3, respectively.

A chiral spirofluorene‐embedded multiple‐resonance thermally activated delayed fluorescence emitter for efficient pure‐green circularly polarized electroluminescence

AbstractThe simultaneous achievement of chiral multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters with narrowband and circularly polarized electroluminescence (CPEL) poses a challenge. Herein, a MR‐TADF emitter, Spiro‐BNCz, embedding spirofluorene structure was developed and chiral separated, whose emission peaks at 528 nm in toluene with Commission Internationale de L'Eclairage coordinates of (0.26, 0.69). The conjugation extension caused by embedding sulfur substituted spirofluorene on B/N framework shortens the singlet‐triplet energy gap and increases spin‐orbital coupling matrix element. Therefore, a fast reverse intersystem crossing rate constant of 2.8 × 106 s−1 and a high photoluminescence efficiency of 92% in film were achieved. The organic light‐emitting diode (OLED) exhibits a maximum external quantum efficiency of 32.3%. Particularly, the circularly polarized OLEDs based on Spiro‐BNCz enantiomers show symmetric CPEL with dissymmetry factors (|gEL|) ≈ 10−3.

A Simple Molecular Design Strategy for Luminescent Radicals to Achieve Near-Infrared Emission.

The spin-allowed doublet emission of luminescent radicals has recently attracted significant attention. However, the spectral range of most reported luminescent radical emitters and their corresponding organic light-emitting diodes (OLEDs) is confined to the red and deep red regions, with only a few extending to the near-infrared region, specifically in the context of an emission peak exceeding 800 nm. Herein, a luminescent radical, 2-(4-(bis(2,4,6-trichlorophenyl)methyl radical)-3,5-dichlorophenyl)-4-phenyl-4H-thieno[3,2-b]indole (TTM-2PTI), with NIR emission peaking at 830 nm in toluene, was obtained through attaching a 4-phenyl-4H-thieno[3,2-b]indole group to the TTM radical core. An organic light-emitting diode (OLED) utilizing TTM-2PTI as the emitter exhibits electroluminescence (EL) emission peaking at 870 nm, which is the longest EL wavelength among the doublet-emissive near-infrared (NIR) OLEDs. This work provides a simple molecular design strategy to achieve NIR emission of radicals by leveraging the lower steric hindrance and electron-donating ability of thiophene.

Circularly polarized luminescence of Hetero[n]helicenes with 2,1,3-thiadiazole rings at both ends: Design of magnetically-allowed electronic transitions via heteroatom embedding

Design of excellent circularly polarized luminescence (CPL) emitters requires chiral molecules with large transition magnetic dipole moments (TMDM, |m|). In this work [5]-, [7]-, and [9]helicene derivatives with 2,1,3-thiadiazole rings at both ends, TD[5]H, TD[7]H, and TD[9]H, were designed and synthesized. We revealed that TD[9]H showed an excellent CPL with a large glum of +0.04 at 520 nm in toluene, which was significantly larger than that of unsubstituted carbo[7]helicene (glum = +0.008). Density functional theory (DFT) calculations suggested that the remarkable glum of TD[9]H was attributed to the magnetically allowed transition with a large TMDM (|m| = 2.3 × 10−20 erg G−1) for the S1→S0 transition.

Design of DAMC dye as a liquid scintillator for gamma ray detection

In this work, we designed a highly sensitive liquid scintillator (LS) based on 7-Diethylamino-4-methylcoumarin (DAMC) dye to detect gamma rays and localize Compton edges (CEs). The absorption and fluorescence peaks of DAMC at a concentration of 0.03 wt%. are 350 nm and 450 nm in toluene, respectively. Typical Photomultiplier tube (PMT) photocathodes have a high quantum yield in the 400 nm–470 nm region, where DAMC emission is most intense. The LS is packaged in a standard glass container with a 2.54 × 2.54 cm diameter and height. Different gamma radiation sources, including 137Cs, 60Co, and 22Na, were used to record LS responses for varying concentrations of DAMC in toluene. The results are compared with LS of the same concentration made with POPOP. The CE was determined by fitting the shoulder and tail of the pulse height distribution spectrum with a Gaussian-based distribution technique. In short, the CE was obtained at the half-height of the gaussian based distribution's fitting. The detector model created by GEANT4, a Monte Carlo code, was compared to the theoretical and experimental results. The CE location was obtained for both ionizing radiation interactions, and scintillation photon transit was simulated using the code. Finally, the experimental spectra were compared to the GEANT4 simulation for calibration, and the CEs were located.

Integrating Asymmetric O-B-N Unit in Multi-Resonance Thermally Activated Delayed Fluorescence Emitters towards High-Performance Deep-Blue Organic Light-Emitting Diodes.

Developing deep-blue thermally activated delayed fluorescence (TADF) emitters with both high efficiency and color purity remains a formidable challenge. Here, we proposed a design strategy by integrating asymmetric oxygen-boron-nitrogen (O-B-N) multi-resonance (MR) unit into traditional N-B-N MR molecules to form a rigid and extended O-B-N-B-N MR π-skeleton. Three deep-blue MR-TADF emitters of OBN, NBN and ODBN featuring asymmetric O-B-N, symmetric N-B-N and extended O-B-N-B-N MR units were synthesized through the regioselective one-shot electrophilic C-H borylation at different positions of the same precursor. The proof-of-concept emitter ODBN exhibited respectable deep-blue emission with Commission International de l'Eclairage coordinate of (0.16, 0.03), high photoluminescence quantum yield of 93 % and narrow full width at half maximum of 26 nm in toluene. Impressively, the simple trilayer OLED employing ODBN as emitter achieved a high external quantum efficiency up to 24.15 % accompanied by a deep blue emission with the corresponding CIE y coordinate below 0.1.

Integrating Asymmetric O−B−N Unit in Multi‐Resonance Thermally Activated Delayed Fluorescence Emitters towards High‐Performance Deep‐Blue Organic Light‐Emitting Diodes

AbstractDeveloping deep‐blue thermally activated delayed fluorescence (TADF) emitters with both high efficiency and color purity remains a formidable challenge. Here, we proposed a design strategy by integrating asymmetric oxygen‐boron‐nitrogen (O−B−N) multi‐resonance (MR) unit into traditional N−B−N MR molecules to form a rigid and extended O−B−N−B−N MR π‐skeleton. Three deep‐blue MR‐TADF emitters of OBN, NBN and ODBN featuring asymmetric O−B−N, symmetric N−B−N and extended O−B−N−B−N MR units were synthesized through the regioselective one‐shot electrophilic C−H borylation at different positions of the same precursor. The proof‐of‐concept emitter ODBN exhibited respectable deep‐blue emission with Commission International de l′Eclairage coordinate of (0.16, 0.03), high photoluminescence quantum yield of 93 % and narrow full width at half maximum of 26 nm in toluene. Impressively, the simple trilayer OLED employing ODBN as emitter achieved a high external quantum efficiency up to 24.15 % accompanied by a deep blue emission with the corresponding CIE y coordinate below 0.1.

A Series of Soluble Planar Oligorylenes up to Hexarylene†

Comprehensive SummaryPreparation of large rylenes often needs the use of solubilizing groups along the rylene backbone, which results in the distortion of the skeleton and thus broadening of the absorption spectrum. In this work, we successfully synthesized 2,5,8,16,19,22‐hexakis[2,6‐ bis(tri‐fluoromethyl)phenyl]hexarylene (H) by using an oxidative fusion reaction of perylene trimer in 5% yield. The product is soluble in common organic solvents and could be purified with column chromatography. Single‐crystal X‐ray diffraction analysis revealed that the hexarylene core is not disturbed by the substituents very much and is almost planar. The longest absorption of H exhibits a sharp peak at 831 nm and an on‐set at 875 nm in toluene with a small full‐width‐at‐half‐maximum (FWHM) of 660 cm‐1. The molar extinction coefficient is as large as 131,000 M‐1 cm‐1. The substituents could not perturb the electronic properties of the hexarylene because aryl groups are perpendicular to the hexarylene core and the carbon atoms at 2,5,16,19‐positions have negligible coefficients on its HOMO and LUMO, estimated by theoretical calculations. As a result, the hexarylene having less absorption at the visible light region was stable enough in solution under the LED room light for more than 1 week. This strategy gives a useful guideline to establish the near‐infrared materials that exhibit stability under ambient conditions.

Donor Influence on the Optoelectronic Properties of N‐Substituted Tetraphenylimidazole Derivatives

AbstractThree new 1,2,4,5‐tetraphenylimidazole derivatives, 9,9‐dimethyl‐10‐(4‐(2,4,5‐triphenyl‐1H‐imidazol‐1‐yl)phenyl)‐9,10‐dihydroacridine (DMAC‐TPI), 10‐(4‐(2,4,5‐triphenyl‐1H‐imidazol‐1‐yl)phenyl)‐10H‐phenoxazine (PXZ‐TPI), and 10‐(4‐(2,4,5‐triphenyl‐1H‐imidazol‐1‐yl)phenyl)‐10H‐phenothiazine (PTZ‐TPI), bearing different electron donors at the N1 position of the imidazole were synthesised and characterised. DMAC‐TPI and PXZ‐TPI showed narrow emission at λPL of 388 and 418 nm in toluene, and in doped films in Zeonex polymer (1 wt.%) at λPL 381 and 407 nm, respectively, with a full width at half maximum (FWHM) ranging 0.42‐0.44 eV. DMAC‐TPI and PXZ‐TPI are predicted to show very low oscillator strength for the low‐energy transitions, which aligns to the observed low photoluminescence quantum yields. Both molecules showed a singlet‐triplet energy gap (ΔEST of around 1.2 eV) that is much too large to enable reverse intersystem crossing and thermally activated delayed fluorescence. Connecting a donor group to TPI at the N1 position can lead to room temperature phosphorescence (RTP), as the example of PTZ‐TPI showed.

Tris(4'-Nitrobiphenyl)amine─An Octupolar Chromophore with High Two-Photon Absorption Cross-Section and Its Application for Uncaging of Calcium Ions in the Near-Infrared Region.

Compounds with high two-photon absorption (2PA) performance in the near-infrared region have attracted great attention because of their application in the material and biological science. In this study, we have developed a simple and novel octupolar chromophore, tris(4'-nitrobiphenyl)amine 1, with three nitro peripheral groups attached to a triphenylamine core via biphenyl linkers. A mono-branched analogue 2 has also been prepared to investigate the effects of octupolar and dipolar systems on photophysical and 2PA behaviors. Compound 1, despite having a much simpler structure than the previous three-branched scaffolds, exhibits comparable σ2 values, reaching 1330 GM at 730 nm and 900 GM at 820 nm in toluene. Combined with an outstanding σ2/MW ratio (2.2 GM g-1 mol) and a high fluorescence quantum yield (0.51), 1 displays potential as a promising two-photon (2P) probe for bioimaging. Subsequently, the ethylene glycol tetraacetic acid-substituted derivatives featuring octupolar (3 and 5) or dipolar (4 and 6) character have been synthesized and their one-photon (1P) and 2P photochemical reactions have been examined. Finally, 1P- and 2P-triggered uncaging of Ca2+ from these calcium chelators has been confirmed.

Near-infrared-red-orange thermally activated delayed fluorescence emitters using a strong tetracoordinated difluoroboronated acceptor

We design two organoboron-based thermally activated delayed fluorescence (TADF) molecules, DMAC-PAPB and m-DMAC-PAPB, containing a strong tetracoordinated difluoroboronated acceptor, a phenyl-linking difluoro[amidopyrazinato-O,N]boron (APB) moiety, named PAPB. Theoretical calculations predict that PAPB has a deep lowest unoccupied molecular orbital (LUMO) energy level. DMAC-PAPB and m-DMAC-PAPB show a low-lying lowest excited singlet state (S1) with small S1 energy (2.04 eV and 1.85 eV, respectively), and small energy gaps (∼0.01 eV) between S1 and the lowest triplet state, which satisfy the critical requisite for constructing red TADF emitters. Experimentally, DMAC-PAPB and m-DMAC-PAPB show red and near-infrared (NIR) luminescence with the peak photoluminescence wavelength at 650 nm and 701 nm in toluene, respectively. The solution-processed doped films both exhibit orange-to-red luminescence and obvious delayed fluorescence. These investigations exemplify the strong electron-accepting ability of PAPB and its potential in developing yellow, orange, red, and NIR organoboron-based TADF emitters.