Spirobifluorene Research Articles

Dual-phase microporous polymer nanofilms by interfacial polymerization for ultrafast molecular separation.

Fine-tuning microporosity in polymers with a scalable method has great potential for energy-efficient molecular separations. Here, we report a dual-phase molecular engineering approach to prepare microporous polymer nanofilms through interfacial polymerization. By integrating two micropore-generating units such as a water-soluble Tröger's base diamine (TBD) and a contorted spirobifluorene (SBF) motif, the resultant TBD-SBF polyamide shows an unprecedentedly high surface area. An ultrathin TBD-SBF membrane (~20 nm) exhibits up to 220 times improved solvent permeance with a moderate molecular weight cutoff (~640 g mol-1) compared to the control membrane prepared by conventional chemistry, which outperforms currently reported polymeric membranes. We also highlight the great potential of the SBF-based microporous polyamides for hydrocarbon separations by exploring the isomeric effects of aqueous phase monomers to manipulate microporosity.

Spirobifluorene-based hole-transporting materials for RGB OLEDs with high efficiency and low efficiency roll-off.

In this work, we designed and synthesized three spirobifluorene (SBF)-based hole-transporting materials (HTMs) by incorporating the di-4-tolylamino group at different positions of the SBF skeleton. These materials demonstrate excellent thermal stability with thermal decomposition temperatures (T d) up to 506 °C and outstanding morphological stability with a glass transition temperature (T g) exceeding 145 °C. The meta-linkage mode between the conjugated skeleton and functional groups in the molecular structure results in electronic decoupling, giving these 3,6-substituted SBFs higher triplet energies (E T) compared to 2,7-substituted SBFs. This makes the 3,6-substituted SBFs suitable as universal HTMs for red, green, and blue (RGB) organic light emitting diodes (OLEDs). Among the three HTMs, 3,3',6,6'-tetra(N,N-ditolylamino)-9,9'-spirobifluorene (3,3',6,6'-TDTA-SBF) exhibits the best device performance, achieving maximum external quantum efficiencies (EQEmax) of 26.1%, 26.4%, and 25.4% for RGB phosphorescent OLEDs, with extremely low efficiency roll-off in both green and blue devices. Utilizing 3,3',6,6'-TDTA-SBF as the HTM, we have also fabricated narrowband blue OLEDs based on the widely used multiple resonance emitter BCz-BN, which exhibits a EQEmax of 29.8% and low efficiency roll-off.

High-performance deep-blue electroluminescence from multi-resonance TADF emitters with a spirofluorene-fused double boron framework.

The development of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials in the deep-blue region is highly desirable. A usual approach involves constructing an extended MR-TADF framework; however, it may also intensify aggregate-caused quenching issues and thereby reduce device efficiency. In this study, we develop a molecular design strategy that fuses the MR-TADF skeleton with 9,9'-spirobifluorene (SF) units to create advanced deep-blue emitters. The SF moiety facilitates high-yield one-shot bora-Friedel-Crafts reaction towards an extended skeleton and mitigates interchromophore interactions as a steric group. Our findings reveal that orbital interactions at the fusion site significantly influence the electronic structure, and optimizing the fusion mode allows for the development of emitters with extended conjugation length while maintaining non-bonding character. The proof-of-concept emitter exhibits narrowband emission in the deep-blue region, a near-unity photoluminescence quantum yield, and a fast k RISC of 2.4 × 105 s-1. These exceptional properties enable the corresponding sensitizer-free OLED to achieve a maximum external quantum efficiency (EQEmax) of 39.0% and Commission Internationale de l'Eclairage (CIE) coordinates of (0.13, 0.09). Furthermore, the hyperfluorescence device realizes an EQEmax of 40.4% with very low efficiency roll-off.

Direct C-H Arylation Derived Ternary D-A Conjugated Polymers: Effects of Monomer Geometries, D/A Ratios, and Alkyl Side Chains on Photocatalytic Hydrogen Production and Pollutant Degradation.

Donor-acceptor (D-A) conjugated polymer (CP) featuring high charge mobility and widely tunable energy bands have shown promising prospects in photocatalysis. In this work, a library of ternary D-A CPs (22 polymers) based on benzothiadiazole, bithiophene, and fluorene derivatives (i.e., fluorene [Fl], 9,9-dihexylfluorene [HF], and 9,9'-spirobifluorene [SF]) with and without alkyl side chains, and with 3D geometry are designed and synthesized via atom-economical direct C-H arylation polymerization to explore the synergetic effects of stereochemistry, D/A ratio, and alkyl chains on the properties and photocatalytic performances, which reveal that 1) the cross-shaped 3D spirobifluorene (SF) building block shows the highest hydrogen evolution rates (HER) owing to the sufficient photocatalytic active sites exposed, 2) the alkyl-free linear polymer (FlBtBT0.05 ) exhibit the highest photocatalytic pollutant degradation performance owing to its superior charge separation, and 3) the alkyl side chains are redundances that will exert detrimental effects on the aqueous photocatalysis owing to their insulating and hydrophobic property. The structure-property-performance correlation results obtained will provide a desirable guideline for the rational design of CP-based photocatalysts.

Benzotriazole-based 3D 4-Arm Small Molecules Enable 19.1% Efficiency for PM6:Y6-based Ternary Organic Solar Cells.

The third component featuring a planar backbone structure similar to the binary host molecule has been the empirical formula for improving the photovoltaic performance of ternary organic solar cells (OSCs). In this work, we explored a new avenue that introduces 3-dimensional structured molecules as guest acceptors. Spirobifluorene (SF) is chosen as the core to combine with three different terminal-modified (rhodanine, thiazolidinedione, and dicyano-substituted rhodanine) benzotriazole (BTA) units, affording three 4-arm molecules, SF-BTA1, SF-BTA2, and SF-BTA3, respectively. After adding these three materials into the classical system PM6: Y6, the resulting ternary devices obtained ultra-high power conversion efficiencies (PCEs) of 19.1%, 18.7%, and 18.8%, respectively, compared with the binary OSCs (PCE = 17.4%). SF-BTA1-3 can work as energy donors to increase charge generation via energy transfer. In addition, the charge transfer between PM6 and SF-BTA1-3 also acts to enhance charge generation. Introducing SF-BTA1-3 could form acceptor alloys to modify the molecular energy level and inhibit the self-aggregation of Y6, thereby reducing energy loss and balancing charge transport. Our success in 3D multi-arm materials as the third component shows good universality and brings a new perspective. The further functional development of multi-arm materials could make OSCs more stable and efficient.

Benzotriazole‐Based 3D Four‐Arm Small Molecules Enable 19.1 % Efficiency for PM6 : Y6‐Based Ternary Organic Solar Cells

AbstractA third component featuring a planar backbone structure similar to the binary host molecule has been the preferred ingredient for improving the photovoltaic performance of ternary organic solar cells (OSCs). In this work, we explored a new avenue that introduces 3D‐structured molecules as guest acceptors. Spirobifluorene (SF) is chosen as the core to combine with three different terminal‐modified (rhodanine, thiazolidinedione, and dicyano‐substituted rhodanine) benzotriazole (BTA) units, affording three four‐arm molecules, SF‐BTA1, SF‐BTA2, and SF‐BTA3, respectively. After adding these three materials to the classical system PM6 : Y6, the resulting ternary devices obtained ultra‐high power‐conversion efficiencies (PCEs) of 19.1 %, 18.7 %, and 18.8 %, respectively, compared with the binary OSCs (PCE=17.4 %). SF‐BTA1‐3 can work as energy donors to increase charge generation via energy transfer. In addition, the charge transfer between PM6 and SF‐BTA1‐3 also acts to enhance charge generation. Introducing SF‐BTA1‐3 could form acceptor alloys to modify the molecular energy level and inhibit the self‐aggregation of Y6, thereby reducing energy loss and balancing charge transport. Our success in 3D multi‐arm materials as the third component shows good universality and brings a new perspective. The further functional development of multi‐arm materials could make OSCs more stable and efficient.

Positional Isomers of Phenylacridine/Spirobifluorene as Deep‐Blue Fluorescent Emitters for Organic Light‐Emitting Diodes

AbstractDesigning deep‐blue fluorophores with a low CIEy is an important request for organic light‐emitting diode (OLED) technology either for display applications or to develop new applications such as light source with antibacterial properties. The challenge of deep‐blue emitting OLEDs mainly relies on the difficulty to reach efficient emitters fulfilling all the characteristics desired to insure a high device performance with suitable CIE coordinates. Herein, we report on the synthesis, the physico‐chemical properties and the application as emissive layer in an OLED of two deep‐blue emitters constructed on the association of Spirofluorene‐N‐PhenylAcridine (SPA‐F) and SpiroBiFluorene (SBF) molecular fragment. Two emitters, 2,2‐SPAF‐SBF and 2,3‐SPAF‐SBF have been constructed following a similar design strategy. The emission wavelength is tuned by the substitution pattern of the SBF backbone (meta or para linkage). Through a structure/properties relationship study, the electrochemical, photophysical and thermal/morphological properties are discussed. When used as emitter in a multi‐layer OLED, 2,2‐SPA‐SBF displays a deep‐blue emission reaching an EQE of ≈1.7% and a Von of 4 V. The electroluminescent spectrum displays a λmax below 400 nm (i.e. 394 nm) and CIE coordinates of (0.182, 0.054). The CIEy coordinate of 0.054 is low and fits the NTSC and EBU standards.

Synthesis of spirobifluorene derivatives via metal catalyzed C[sbnd]N and C[sbnd]C cross couplings: useful substrate for cadmium ion sensing

We report, a simple synthetic strategy involving C—N and C–C cross-coupling reactions starting with spirobifluorene (SBF) catalyzed by transition metal (Cu and Pd) catalysts. The promising applications of SBF derivatives inspired us to carry out this investigation. Various heterocyclic coupling partners having electron-rich and electron-deficient functionalities (e.g., pyrrole, pyrazole, imidazole, triazole, and phenylboronic acids) are used in this study. The extended conjugation present in the cross-coupling products makes them suitable candidates for fluorescent study. Among the synthesized substrates, spirobifluorene- terphenyl amine (SBF-TA) emission spectra displayed a significant fluorescence enhancement against the Cd(II) ion which has a detection limit of 20 nM.

Synthesis of cross-linked conducting copolymers containing twisted spirobifluorene units via direct arylation random copolymerization for electrochromic applications

Two cross-linked copolymers containing twisted spirobifluorene (SBF) units are successfully synthesized via direct arylation polymerization (DArP) with a low reaction temperature and catalyst addition. The resultant polymers are fully characterized by H Nuclear magnetic resonance (HNMR), gel permeation chromatography (GPC), thermo gravimetric analysis (TGA), Fourier Transform infrared spectroscopy (FTIR), Cyclic voltammogram (CV). Spectroelectrochemical measurements indicate the synthesized polymers possess wide band gap and red color in their neutral state. After applying an oxidized potential, the polymer films are highly transparent in their oxidized state. Additionally, two electrochromic devices are assembled based on these two copolymers, which demonstrate good optical contrast, fast switching response and good stability, indicating the incorporation of SBF units into the poly(3,4-alkyldioxythiophene) mainchain can induce the synthesis of high-performance red-to-transparent electrochromic polymers.

Porosity Engineering of Hyper-Cross-Linked Polymers Based on Fine-Tuned Rigidity in Building Blocks and High-Pressure Methane Storage Applications

Exploring the effect of the structural rigidity of selected building blocks on the resultant porosity of the desired polymers is crucial for the bottom-up design of hyper-cross-linked polymers. Herein, several novel polymers, based on two series building blocks with stepwise fine-tuned rigidity, were constructed by the low-cost solvent knitting method. Significantly, the porosity of these polymers is highly consistent with the structural rigidity of the basic building blocks, dramatically enhanced from a poor porous state to a micropore-rich framework, with an increase in BET surface areas from 248 to 1276 m2 g–1 for the HCPs based on monomers containing double benzene rings and from 37 to 2368 m2 g–1 for tetraphenyl-like monomer-based HCPs. The best performances, especially concerning methane adsorption capacity, are reached for the rigid 9,9′-spirobifluorene (SBF)-based HCP-SBF framework and flexible tetraphenylmethane (TPM)-based HCP-TPM, showing a 5–100 bar working capacity of 206 cm3 (STP: 273 K, 1 atm) cm–3 (0.296 g g–1) and 199 cm3 (STP) cm–3 (0.112 g g–1) at 273 K, respectively. The bottom-up-designed HCPs with engineered porosity are expected to become novel candidates for onboard methane storage.

A two-armed skeleton extension strategy for the design of novel spirobifluorene-based small molecule donors

A two-armed extension design strategy based on Spirobifluorene (SF) was employed to regulate the optoelectronic properties of the materials. As the most important result, the devices based on SF(DPPCz)2/PC71BM exhibit the highest PCE of 8.12%.

Robust Spirobifluorene Core Based Hole Transporters with High Mobility for Long-Life Green Phosphorescent Organic Light-Emitting Devices.

Using a tailored high triplet energy hole transport layer (HTL) is a suitable way to improve the efficiency and extend the lifetime of organic light-emitting devices (OLEDs), which can use all molecular excitons of singlets and triplets. In this study, dibenzofuran (DBF)-end-capped and spirobifluorene (SBF) core-based HTLs referred as TDBFSBF1 and TDBFSBF2 were effectively developed. TDBFSBF1 exhibited a high glass transition temperature of 178 °C and triplet energy of 2.5 eV. Moreover, a high external quantum efficiency of 22.0 %, long operational lifetime at 50 % of the initial luminance of 89,000 h, and low driving voltage at 1000 cd m-2 of 2.95 V were achieved in green phosphorescent OLEDs using TDBFSBF1. Further, a high-hole mobility μh value of 1.9×10-3 cm2 V-1 s-1 was recorded in TDBFSBF2. A multiscale simulation successfully reproduced the experimental μh values and indicated that the reorganization energy was the primary factor in determining the mobility differences among these SBF core based HTLs.

An efficient aggregation‐enhanced delayed fluorescence luminogen created with spiro donors and carbonyl acceptor for applications as an emitter and sensitizer in high‐performance organic light‐emitting diodes

AbstractOrganic light‐emitting diodes (OLEDs) fabricated using organic thermally activated delayed fluorescence materials as sensitizers have recently achieved significant advancements, but the serious efficiency roll‐offs are still troublesome in most cases. Herein, a tailor‐made multifunctional luminogen SBF‐BP‐SFAC containing 9,9′‐spirobifluorene (SBF) and spiro[acridine‐9,9‐fluorene] (SFAC) as electron donors and carbonyl as an electron acceptor is synthesized and characterized. SBF‐BP‐SFAC has the advantages of high thermal stability, aggregation‐enhanced delayed fluorescence, and balanced carrier transport ability, and prefers horizontal dipole orientation. Highly efficient OLEDs employing SBF‐BP‐SFAC as an emitter radiate intense cyan light with outstanding external quantum efficiencies (ηexts) of up to 30.6%. SBF‐BP‐SFAC can also serve as an excellent sensitizer for orange fluorescence, phosphorescence, and delayed fluorescence materials, providing excellent ηexts of up to 30.3% with very small efficiency roll‐offs due to the fast Förster energy transfer as well as exciton annihilation suppression by bulky spiro donors. These outstanding performances demonstrate the great potential of SBF‐BP‐SFAC as an emitter and sensitizer for OLEDs.

Fluorene Derivatives for Efficient Prompt Scintillation in Plastic Scintillators

Plastic scintillators have been investigated for γ-ray detection with the promise of fast response, ease of scale up, and mechanical toughness. However, their low light yield has been a major limiting factor in the performance metrics. Herein, we report a cross-linkable fluorene derivative, 9,9-bis(4-vinylbenzyl)-9H-fluorene (SF), copolymerized with the plastic matrix, to facilitate effective Förster resonance energy transfer to boost the light yield. Noncurable 9,9-dimethyl-9H-fluorene (MF) and 9,9′-spirobifluorene (SBF) were also introduced to bridge the energy transfer gap between the polymer matrix and the primary dye. The plastic scintillator comprising 5 wt % SF and 20 wt % MF exhibits a light yield of 11 600 photons/MeV with a scintillation decay time constant of 2.3 ns.

A Tetracyanobutadiene Spirobifluorene: Synthesis, Enantiomeric Resolution and Chiroptical Properties

AbstractPush‐pull organic compounds with π‐conjugated backbones are attracting considerable interest in terms of their highly efficient (NLO) non‐linear optical effects. In this respect, cyano groups constitute one of the strongest electron acceptors suitable for NLO materials. We herein report the first 1,1,4,4‐tetracyanobutadiene (TCBD) spirobifluorene (SBF) through a double [2+2] cycloaddition‐retroelectrocyclization. Enantiomeric resolution by HPLC using a chiral stationary phase (CSP) and theoretical calculations unveiled not only the nature of the potential energy surface, but also the absolute configuration of each enantiomer. Since both the presence of strong donor and acceptor, as well as the intrinsic non‐centrosymmetric character of chiral compounds are a prerequisite for the development of NLO properties, the first hyperpolarizability of the developed system was theoretically calculated. The results suggested a strong dependence on the conformation and an intensity enhancement for certain conformers of 1 as compared to its allenic TCBD analogue. Therefore, the present study opens a new class of SBF compounds suitable for NLO applications.

Water‐Soluble Organic Dyes as Efficient Anode Interlayer Materials for PEDOT:PSS‐Free Inverted Bulk Heterojunction Solar Cells

Solution‐processed inverted organic solar cells (OSCs) generally use poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate (PEDOT:PSS) as hole selective anode interlayer (AIL). However, the acidic nature of PEDOT:PSS considerably accelerates the degradation dynamics of OSCs, which shortens the durability of these low‐cost photovoltaic devices. Small organic molecules are attracting growing interest as alternative AIL materials, but their solubility limited to toxic organic solvents hinders the production of environmentally friendly OSCs. Herein, the first inverted OSCs employing non‐PEDOT:PSS solution‐processed top small organic molecule AILs deposited from aqueous solution are reported. The investigated water‐soluble spirobifluorene (SBF) derivatives 1 and 2 show hole mobility (≈4 × 10−3 cm2 V−1 S−1) higher than PEDOT:PSS. Because of their nonacidic nature, the interlayers formed with derivatives 1 or 2 considerably delay the degradation of the top metal electrode compared to OSCs employing PEDOT:PSS interlayers. The PEDOT:PSS‐free OSC devices with inverted configuration with the water‐soluble SBF derivatives as AIL produce power conversion efficiencies above 5% with PTB7‐Th:ITIC active layers and above 8% with PBDB‐T‐2Cl:Y6 active layers, respectively, with an enhancement up to 28% compared to OSCs employing PEDOT:PSS. These results correspond to the highest reported values for PEDOT:PSS‐free small‐molecule inverted OSCs deposited from an aqueous solution.

New Exciplex‐Forming Co‐Host System and Thienothiadazole‐based Fluorescent Emitter for High‐Efficiency and Promising Stability Near‐Infrared OLED

AbstractTwo new spirobifluorene (SF)‐centered donors (D) DPSF and DTSF are developed to blend with acceptor (A) CN‐T2T for exciplex formation. The transient photoluminescence characterizations of pristine donor and D:A blended films verify the donor aggregates emissions that lead to relatively low photoluminescence quantum yield (PLQY) of exciplex emission. However, the charge recombination at lower energy exciplex state leads the device with DPSF:CN‐T2T blend to give electroluminescence (EL) λmax of 584 nm and external quantum efficiency (EQE) of 6.0%. The DPSF:CN‐T2T exciplex excitons are efficiently extracted by a D‐A‐D‐type fluorescence emitter TTDSF comprising thienothiadiazole core and SF peripherals via Förster energy transfer to give near‐infrared (NIR) emission (760 nm, PLQY 26%). After the electron‐transporting layer thickness optimization, the device with DPSF:CN‐T2T: 7 wt.% TTDSF as emitting layer affords EL λmax 774 nm and EQE up to 5.3%, one of the best cases in NIR organic light‐emitting diodes (OLEDs). More importantly, the device stability has been examined to display an excellent lifetime (LT95 > 200 hours). This work manifests the judicious combination of an exciplex‐forming co‐host system and a designated NIR emitter equipping with a high quinoidal core and rigid peripheral SF groups that can realize an efficient NIR OLED.

3D Carbiyne Nanospheres Boosting Excellent Lithium and Sodium Storage Performance.

Reasonable design of electrode materials with specific morphology and structure can efficiently improve the metal ions storage and transmission properties of metal ion batteries. Here the preparation of spirobifluorene-based three-dimensional carbiyne nanosphere (SBFCY-NS) that is composed of spirobifluorene (SBF) and alkyne bonds is reported. Benefiting from the rigid spatial structure of SBF, numerous precursors are coupled through the connection of acetylene bonds, extending to form solid nanospheres. Abundant storage spaces and convenient multi-directional transmission paths for metal ions are available inside the three-dimensional (3D) carbiyne structure. Thus, SBFCY-NS is applied as efficient anode for lithium-ion battery and sodium-ion battery. The good stability of SBFCY-NS-based electrode and its improved Coulombic efficiency can be attributed to the special morphology of nanospheres, which can easily form thin and stable solid electrolyte interface film on the surface. Those results further promote the preparation of spherical carbon-based materials with abundant pores that can be applied in the field of electrodes.

Multifunctional Materials Serving as Efficient Non‐Doped Violet‐Blue Emitters and Host Materials for Phosphorescence

Efficient multifunctional materials acting as violet-blue emitters, as well as host materials for phosphorescent OLEDs, are crucial but rare due to demand that they should have high first singlet state (S1 ) energy and first triplet state (T1 ) energy simultaneously. In this study, two new violet-blue bipolar fluorophores, TPA-PI-SBF and SBF-PI-SBF, were designed and synthesized by introducing the hole transporting moiety triphenylamine (TPA) and spirobifluorene (SBF) unit that has high T1 into high deep blue emission quantum yield group phenanthroimidazole (PI). As the results, the non-doped OLEDs based on TPA-PI-SBF exhibited excellent EL performance with a maximum external quantum efficiency (EQEmax ) of 6.76 % and a violet-blue emission with Commission Internationale de L'Eclairage (CIE) of (0.152, 0.059). The device based on SBF-PI-SBF displayed EQEmax of 6.19 % with CIE of (0.159, 0.049), which nearly matches the CIE coordinates of the violet-blue emitters standard of (0.131, 0.046). These EL performances are comparable to the best reported non-doped deep or violet-blue emissive OLEDs with CIEy<0.06 in recent years. Additionally, the green, yellow and red phosphorescent OLEDs with TPA-PI-SBF and SBF-PI-SBF as host materials achieved a high EQEmax of about 20 % and low efficiency roll-off at the ultra-high luminance of 10 000 cd m-2 . These results provided a new construction strategy for designing high-performance violet-blue emitters, as well as efficient host materials for phosphorescent OLEDs.

Structure–Property Relationship on Aggregation-Induced Enhanced Emission of the Spirobifluorene Derivatives including Herringbone, T, and Helical Aggregation Mode in Solid-Phase: Synthesis, Crystallography, Density Functional Theory, Optical, and Thermal Properties

The development of efficient luminescent materials in the solid state attracts great attention for their potential applications. Based on this importance, we presented the structure–property relationship of the spirobifluorene (SBF) derivative molecules by photophysical studies and single-crystal X-ray crystallography and very important luminogens having aggregation-induced emission behavior in the solid state. Also, cyclic voltammetry (CV), thermogravimetric analysis (TGA), spectroscopic, and theoretical studies of these molecules are presented. We show that the molecular structure, conformational twisting, structural rigidity, and supramolecular packing play significant roles in the SBF molecules’ photoluminescence behavior, especially in determining whether they are aggregation-induced emission -active. These molecules demonstrated enhanced emission in the supramolecular aggregate state created by herringbone-, helical-, and T-type π···π stacking interactions compared to that of the solution phase. Moreover, the restricted intramolecular rotation has been demonstrated to play a significant role in the aggregation-induced enhanced emission properties of the SBF molecules. The most increasing in PL intensity was observed in the molecule SBF1 and SBF3 with the T- and helical-type stacking interactions, respectively. We concluded that the helical- and T-type stacking modes with a small perpendicular distance result in high fluorescence intensity in the SBF molecules’ aggregate state. This study will provide an overview of supramolecular arrangements on the solid-state optoelectronic properties of SBF derivatives. Also, it would suggest new pathways toward targeted molecular design strategies.