Spirobifluorene Moiety Research Articles

Thiazolo[5,4-d]thiazoles with a spirobifluorene moiety as novel D–π–A type organic hosts: design, synthesis, structure–property relationship and applications in electroluminescent devices

Novel D–π–A type organic small-molecules with thiazolo[5,4-d]thiazole and spirobifluorene units. Optoelectronical properties suggests their applications in materials. Electroluminescent devices containing the novel TzTz-based derivatives 4b, 5b show affinitive emission.

Spirobifluorene-based hole-blocking material with enhanced efficiency through hole and exciton confinement in blue fluorescent OLEDs

A new hole-blocking material, 2-(9,9′-spirobi[fluoren]-5-yl)-4-phenylbenzo [4,5]thieno[3,2-d]pyrimidine (SBF-BTPym), was designed and synthesized using spirobifluorene and electron transport moieties. The high triplet energy and high thermal stability of the spirobifluorene moiety were suitable for designing the hole-blocking material for blue fluorescent organic light-emitting diodes (OLEDs). The electron deficiency of benzothienopyrimidine allowed good electron transport properties, and a deep highest occupied molecular orbital energy level of −6.55 eV suppressed leakage of the holes from the emitting layer (EML) to the adjacent layer. Blue fluorescent OLEDs consisting of a triplet-triplet annihilation–induced host were fabricated using SBF-BTPym. The maximum external quantum efficiency of the blue fluorescent device was 7.2%, which was higher than that of the device without a hole-blocking layer by 10%. According to transient electroluminescence analysis, exciton confinement in the EML is mainly responsible for the improved efficiency.

Synthesis, Stereochemical and Photophysical Properties of Functionalized Thiahelicenes

We report on the synthesis of a novel class of functionalized thia[6]helicenes and a thia[5]helicene, containing a benzothiophene unit and a second heteroatom embedded in the helix (i.e., nitrogen and oxygen) or a pyrene or a spirobifluorene moiety. These systems are obtained through straightforward and general procedures that involve: (i) palladium-catalyzed annulation of iodo-atropoisomers with internal alkynes and (ii) Suzuki coupling of iodo-atropoisomers with phenyl boronic acid followed by a Mallory-type reaction. Both experimental and theoretical studies on the configurational stability of some selected thia[6]helicenes confirmed their stability toward racemization at room temperature, while the pyrene-based thia[5]helicene was found to be unstable. Moreover, the configuration assignment for one representative thiahelicene was established through the comparison between experimental and theoretical circular dichroism (CD) spectra. A systematic study of the photophysical properties of both thiahelicenes and the corresponding atropoisomers has been carried out to provide a complete overview on the new molecules proposed in this work. The obtained data showed regular trends in all the thiahelicene series with spectroscopic traits in line with those previously observed for similar heterohelicenes.

High performance doping-free WOLEDs based on rationally designed asymmetric orange-red Ir(III) emitter with balanced charge mobility

Doping-free organic light-emitting diodes (OLEDs) have attracted continuous attention owing to reduced phase separation, better repeatability, and low cost. Despite demonstrating great potential for white OLEDs (WOLEDs), development of phosphorescent materials capable of achieving high performance with low voltage, high luminance, and low efficiency roll-off simultaneously, still remains a significant challenge. Herein, we design three orange-red Ir(III) phosphors employing functionalized 1,2-diphenylbenzimidazole as main ligands. Clear relationship between structures and electroluminescence (EL)-performances has been established by comprehensively studying their emission properties and intrinsic carrier transporting abilities. Designed phosphor SFIrbiq with spirobifluorene moiety showing negligible intermolecular interactions and balanced carrier transporting ability, not only achieves favorable monochromatic doping-free device but also high-performance doping-free WOLEDs. Optimized WOLED realizes low voltages (2.5 V at 1 cd m−2, 3.3 V at 100 cd m−2, and 4.2 V at 1000 cd m−2), maximum brightness of 34 505 cd m−2 and efficiencies of 24.2 cd A−1, 21.7 lm W−1, 10.3%. Such doping-free hybrid WOLED also achieves low efficiency roll-off of 5% for external quantum efficiency (EQE) at 1000 cd m−2. The device performance can be further improved by employing doping-free all-phosphorescent device structure, achieving maximum efficiencies of 33.3 cd A−1, 32.4 lm W−1, and 16.9%. The results are promising among reported doping-free three-color WOLEDs, paving a feasible way to development of efficient Ir(III) phosphors and doping-free WOLEDs.

Spirobifluorene-Based o-Carboranyl Compounds: Insights into the Rotational Effect of Carborane Cages on Photoluminescence.

9,9'-Spirobifluorene-based closo-o-carboranyl (SFC1 and SFC2) compounds and their nido-derivatives (nido-SFC1 and nido-SFC2) were prepared and characterized. The two closo-compounds displayed major absorption bands assignable to π-π* transitions involving the spirobifluorene group, as well as weak intramolecular charge-transfer (ICT) transitions between the o-carboranes and their spirobifluorene moieties. The nido-compounds exhibited slightly blueshifted absorption bands resulting from the absence of the ICT transitions corresponding to the o-carborane moieties due to the anionic character of the nido-o-carboranes. While SFC1 exhibited only high-energy emissions in THF at 298 K (only from locally excited (LE) states assignable to π-π* transitions on the spirobifluorene group), remarkable emissions in the low-energy region were observed in the rigid state such as in THF at 77 K and in the film state. SFC2 displayed intense emissions in the low-energy region in all states. The fact that neither of the nido-derivatives of SFC1 and SFC2 exhibited low-energy emissions and the TD-DFT calculation results of each closo-compound clearly verified that the low-energy emission was based on ICT-based radiative decay. The conformational barriers from each relative energy calculation upon changing the dihedral angles around the o-carborane cages for both compounds confirmed that the rotation of the o-carborane cages and terminal phenyl rings for SFC1 is freer than that for SFC2.

Linear [3]Spirobifluorenylene: An S-Shaped Molecular Geometry of p-Oligophenyls.

An S-shaped p-oligophenyl derivative was synthesized, as exemplified by linear [3]spirobifluorenylene (R,P,R/S,M,S)-1, which consisted of two p-sexiphenyls tied at the spiro-carbons of three spirobifluorenes. The direct linking of spirobifluorenes results in the formation of strained p-oligophenyl chains, which support each other to maintain the strained structure. This curved structure was successfully constructed by Suzuki-Miyaura cross-coupling of the corresponding spirobifluorene building blocks. Chiral (R,P,R)-1 and (S,M,S)-1 were also synthesized using chiral monomers, and their chiroptical properties were investigated by CD and CPL spectroscopy. The benzene rings in (R,P,R/S,M,S)-1 are distorted with the largest bend angle of 11.6°. The strain energy of (S,M,S)-1 was estimated to be 88.4 kcal/mol, which lies between those for [6] and [7]CPP. Through-space orbital interactions (spiroconjugation) were evaluated by TD-DFT calculations, and the results suggest the contribution of a 15 nm red-shift in (S,M,S)-1 in comparison with the single strand molecule 10. In addition, spiroconjugation is discussed in terms of molecular orbitals, and the splitting of both HOMO and LUMO was revealed by the calculations. The LUMO splitting is particularly interesting, since it is in contrast to the degenerate LUMOs in a simple spirobifluorene. Desymmetrization based on the distortion of the spirobifluorene moieties induces the LUMO splitting.

Spirobifluorene-based oligopyridine derivatives as electron-transporting materials for green phosphorescent organic light-emitting diodes

Abstract The electron-transporting materials (ETMs), 2,7-bis(3,5-di (pyridin-3-yl)phenyl)-9,9′-spirobi [fluorene] (3-4PySF) and 2,7-bis(3,5-di (pyridin-4-yl)phenyl)-9,9′-spirobi [fluorene] (4-4PySF) were designed and synthesized by combining spirobifluorene moiety with di(pyridine-3-yl)phenyl and di(pyridine-4-yl)phenyl, respectively. The spirobifluorene moiety improves materials' rigid twisted structure to ensure the morphological stability of amorphous film, and pyridine acts as electron acceptor to enhance electron-transporting ability of materials. The dependence of electron-transporting property on the position of substituted pyridine rings was studied. The melting point (Tm) of 4-4PySF is estimated to be 41 °C higher than that of 3-4PySF. And the higher current density in the electron only devices exhibited by 4-4PySF revealed the effect of nitrogen atom position on the charge-transporting properties. Green PhOLEDs based on bis(2-phenylpyridine)iridium (III) (2,2,6,6-tetramethylheptane-3,5-diketonate) (Ir (ppy)2tmd) as the emitter and 3-4PySF, 4-4PySF and 1,3,5-tris(N-phenylbenzimid azol-2-yl-benzene (TPBi) as ETMs were fabricated. Compared to the device based on the conventional ETM TPBi, the devices based on new ETMs exhibited a higher maximum external quantum efficiency (EQE) of 20.5% and a lower turn-on voltage (Von) of 2.6 V.

Long‐Lived and Highly Efficient TADF‐PhOLED with “(A)n–D–(A)n” Structured Terpyridine Electron‐Transporting Material

AbstractThe electron‐transporting material (ETM) is one of the key factors to determine the efficiency and stability of organic light‐emitting diodes (OLEDs). A novel ETM with a “(Acceptor)n–Donor–(Acceptor)n” (“(A)n–D–(A)n”) structure, 2,7‐di([2,2′:6′,2″‐terpyridin]‐4′‐yl)‐9,9′‐spirobifluorene (27‐TPSF), is synthesized by combining electron‐withdrawing terpyridine (TPY) moieties and rigid twisted spirobifluorene, in which the TPY moieties facilitate electron transport and injection while the spirobifluorene moiety ensures high triplet energy (T1 = 2.5 eV) as well as enhances glass transition temperature (Tg = 195 °C) for better stability. By using tris[2‐(p‐tolyl)pyridine]iridium(III) (Ir(mppy)3) as the emitter, the 27‐TPSF‐based device exhibits a maximum external quantum efficiency (ηext, max) of 24.5%, and a half‐life (T50) of 121, 6804, and 382 636 h at an initial luminance of 10 000, 1000, and 100 cd m−2, respectively, which are much better than the commercialized ETM of 9,10‐bis(6‐phenylpyridin‐3‐yl)anthracene (DPPyA). Furthermore, a higher efficiency, a ηext, max of 28.2% and a maximum power efficiency (ηPE, max) of 129.3 lm W−1, can be achieved by adopting bis(2‐phenylpyridine)iridium(III)(2,2,6,6‐tetramethylheptane‐3,5‐diketonate) (Ir(ppy)2tmd) as the emitter and 27‐TPSF as the ETM. These results indicate that the derivative of TPY to form “(A)n–D–(A)n” structure is a promising way to design an ETM with good comprehensive properties for OLEDs.

Low-Cost Perovskite Solar Cells Employing Dimethoxydiphenylamine-Substituted Bistricyclic Aromatic Enes as Hole Transport Materials.

The synthesis, characterization and photovoltaic performance of series of novel molecular hole transport materials (HTMs) based on bistricyclic aromatic enes (BAEs) are presented. The new derivatives were obtained following a simple and straightforward procedure from inexpensive starting reagents mimicking the synthetically challenging 9,9'-spirobifluorene moiety of the well-studied spiro-OMeTAD. The novel HTMs were tested in mixed cations and anions perovskite solar cells (PSCs) yielding a power conversion efficiency (PCE) of 19.2 % under standard global 100 mW cm-2 AM1.5G illumination using 9-{2,7-bis[bis(4-methoxyphenyl)amino]-9H-fluoren-9-ylidene}-N2 ,N2 ,N7 ,N7 -tetrakis(4-methoxyphenyl)-9H-thioxanthene-2,7-diamine (coded as KR374). The power conversion efficiency data confirms the easily attainable heteromerous fluorenylidenethioxanthene structure as valuable core for low-cost and highly efficient HTM design and paves the way towards cost-effective PSC technology.

Highly Efficient Perovskite Solar Cells Employing an Easily Attainable Bifluorenylidene-Based Hole-Transporting Material.

The 4,4'-dimethoxydiphenylamine-substituted 9,9'-bifluorenylidene (KR216) hole transporting material has been synthesized using a straightforward two-step procedure from commercially available and inexpensive starting reagents, mimicking the synthetically challenging 9,9'-spirobifluorene moiety of the well-studied spiro-OMeTAD. A power conversion efficiency of 17.8 % has been reached employing a novel HTM in a perovskite solar cells.

Highly Efficient Perovskite Solar Cells Employing an Easily Attainable Bifluorenylidene‐Based Hole‐Transporting Material

AbstractThe 4,4′‐dimethoxydiphenylamine‐substituted 9,9′‐bifluorenylidene (KR216) hole transporting material has been synthesized using a straightforward two‐step procedure from commercially available and inexpensive starting reagents, mimicking the synthetically challenging 9,9′‐spirobifluorene moiety of the well‐studied spiro‐OMeTAD. A power conversion efficiency of 17.8 % has been reached employing a novel HTM in a perovskite solar cells.

Organosoluble and optically active polyamides based on axially asymmetric 9,9′-spirobifluorene moieties

Optically active polyamides containing axially asymmetric 9,9′-spirobifluorene units in the main chain were synthesized for the first time by low-temperature solution polycondensation of ( R)-2,2′-bis(4-amino-2-trifluoromethylphenoxy)-9,9′-spirobifluorene with various diacyl chlorides. All these polymers were obtained in quantitative yields with inherent viscosities of 0.28–0.43 dL g−1. These polyamides were amorphous and readily soluble in many organic solvents such as N-methyl-2-pyrolidone, N, N-dimethylacetamide (DMAc), dimethyl sulfoxide, and tetrahydrofuran. The glass transition temperatures of these polyamides were recorded in the range of 199–261°C by differential scanning calorimetry, and the 10% weight loss temperatures were over 410°C both under nitrogen and in air atmospheres. The specific rotations of these chiral polyamides oscillated between 65.0° and 127.8° depending on the structures of the diacid chlorides. All the optically active polymers exhibited high chiral stability in solid state or in DMAc solvent at high temperature due to incorporation of chiral spirobifluorone unit in polymer backbones. The ultraviolet–visible and circular dichroism spectroscopic properties of these chiral polyamides in solutions were also studied.

A new class of three-dimensional, p-type, spirobifluorene-modified perylene diimide derivatives for small molecular-based bulk heterojunction organic photovoltaic devices

A new class of non-planar and three-dimensional spirobifluorene-modified perylene diimide compounds has been successfully designed and synthesized. The functionalization of the perylene diimide core with different spirobifluorene moieties can alter the molecular geometry as well as extend the spectral coverage into the red region. In addition, these compounds can be utilized as donor materials in combination with fullerene to form bulk heterojunctions, and particularly efficient organic photovoltaic (OPV) devices demonstrating high open-circuit voltages of 0.97 V and a power conversion efficiencies of up to 4% have been prepared. These values are the highest among the cells utilizing p-type perylene diimide as photoactive material in OPV devices. This work opens up a new avenue for the design and synthesis of a new class of p-type perylene diimide compounds that are promising candidates as donor materials in the fabrication of OPV devices.

Molecular recognition of isomeric protonated amino acid esters monitored by ESI-mass spectrometry.

Two new 9,9’-spirobifluorene-derived crown ethers were prepared and used to recognise constitutionally isomeric amino acid derivatives. The performance of the receptors was evaluated by ESI-mass spectrometry using the isomer labelled guest method (ILGM). This method revealed the preferred binding of L-norleucine and L-leucine compared to L-isoleucine for both receptors. Furthermore, non-covalent isotope effects demonstrate the relevance of dispersive interactions for the overall binding event. These effects also provide hints for the relative spatial orientation of the guest molecules within the host–guest complex, and thereby prove the importance of the spirobifluorene moiety for the observed binding of the protonated amino acid esters.

Novel dibenzothiophene based host materials incorporating spirobifluorene for high-efficiency white phosphorescent organic light-emitting diodes

Two host materials, DBTSF2 and DBTSF4, were designed and synthesized, incorporating dibenzothiophene (DBT) and spirobifluorene (SF) blocks. Their thermal, electrochemical and photo-physical properties were fully characterized. DBTSF4, which adopted an ortho-linkage between DBT and SF moieties, showed a significantly higher T1 energy of 2.82eV as compared to its para-linkage analogue DBTSF2 (2.49eV). Their applications as host for green, blue and white phosphorescent organic light-emitting diodes (PHOLEDs) were explored. The DBTSF4 based blue PHOLED has a highest current efficiency of 23.5cdA−1. And using DBTSF4 as a single host, two-color based white PHOLEDs were achieved from cold white emission with CIE coordinate of (0.31, 0.43) to yellowish warm white emission (0.44, 0.49) with maximum current efficiencies varying from 35.8 to 52.3cdA−1 and maximum external quantum efficiencies from 13.1% to 16.9% respectively. The white PHOLED devices also showed a low efficiency roll-off even at 10,000cdm−2.

Spirobifluorene-Based Conjugated Polymers for Polymer Solar Cells with High Open-Circuit Voltage

A new alternating copolymer (PSFDTBT) based on spirobifluorene, thiophene, and benzothiadiazole units has been synthesized. PSFDTBT has an optical band gap of 1.97 eV with the low-lying HOMO energy level at −5.4 eV. The hole mobility of the pristine PSFDTBT film spin-cast from o-dichlorobenzene (DCB) solution is 7.26 × 10–3 cm2 V–1 s–1 with on/off ratios in the order of 105. Polymer solar cell devices based on the blend films of PSFDTBT and PC71BM show a high open-circuit voltage of 0.94 V and a power conversion efficiency of 4.6% without any post-treatment. All the device measurements were performed in air without encapsulation. This is the first report on spirobifluorene-based conjugated polymers used for polymer solar cells, demonstrating the great potential of spirobifluorene moiety as an electron-donating unit for the construction of main chain donor–acceptor alternating conjugated polymers for high performance polymer solar cells.

Synthesis and characterization of luminescent poly(ester-imide) derivatives constituted of alternating spirobifluorene moiety

A new category of luminescent poly(ester-imide)s derivatives based on spirobifluorene rings in the main chain was synthesized from 2,6-bis(4-hydroxybenzylidine)cyclohexanone (BC) derivatives and diimide-dicarboxylic acid (DIDA) containing spirobifluorene moiety. The structure of the polymer was confirmed by elemental and spectral analyses. The various characteristics of the resulting polymers including optical properties, solubility, thermal analysis, and X-ray diffraction analysis were determined and discussed. The new polymers showed relatively high glass-transition temperatures (about 200°C) and good thermal stability. Two polymers emitted blue-greenish light with photoluminescence (PL) emission maxima around 400–600nm and the electron affinity of new polymers was estimated as 2.75–2.84eV. Cyclic voltammetry displayed that both conjugated polymers had reversible oxidation and irreversible reduction, making them n-type electroluminescent materials. [Display omitted]

Electrochemistry and Electrogenerated Chemiluminescence of a Spirobifluorene-Based Donor (Triphenylamine)−Acceptor (2,1,3-Benzothiadiazole) Molecule and Its Organic Nanoparticles

A new D-A-π-A-D molecule (Spiro-BTA) containing two 2,1,3-benzothiadiazole (BTA) as the acceptor (A) and triphenylamine as the donor (D) bridged by a spirobifluorene moiety has been synthesized. The novel D-A molecule shows intense red emission (612 nm) with a high PL quantum yield (Φ(PL) = 0.51) in a solid film. A cyclic voltammogram of Spiro-BTA in 1:2 MeCN:benzene/0.1 M Bu(4)NPF(6) shows two reversible oxidation waves and one reversible reduction wave. The first oxidation wave and reduction wave were assigned as two successive electron transfer peaks separated by ∼50 mV related to the oxidation of the two noninteracting donors and the reduction of the two noninteracting acceptors, respectively. Electrogenerated chemiluminescence (ECL) of Spiro-BTA upon cyclic oxidation and reduction in MeCN:benzene 1:2 shows a very bright and stable red emission that could be seen in a well-lit room. Using a reprecipitation method, well-dispersed organic nanoparticles (NPs) of the Spiro-BTA were prepared in aqueous solution. The nanoparticles were analyzed by dynamic light scattering (DLS) and scanning electron microscopy (SEM), yielding a NP size (without surfactant) of 130 ± 20 nm, while with surfactant, 100 ± 20 nm. Bathochromic shifts of absorption spectra (∼16 ± 2 nm), as compared to that of the dissolved Spiro-BTA in THF, were observed for both NPs in water and as a thin film. While blue shifts (14 ± 2 nm) were observed for the photoluminescence (PL). The PL intensity of the Spiro-BTA nanoparticles was slightly enhanced (Φ(PL) of nanoparticles in water = 48%) over that of the dissolved Spiro-BTA in THF. The ECL of the organic Spiro-BTA nanoparticles in aqueous solution could be observed upon oxidation with tri-n-propylamine as a coreactant.

Efficient triphenylamine-based dyes featuring dual-role carbazole, fluorene and spirobifluorene moieties

Three triphenylamine-based organic dyes SD6, SD7, and SD8 containing the bulky dual-role moieties (fluorene, carbazole, and spirobifluorene) in the molecular frameworks were synthesized, characterized and applied in dye-sensitized solar cells (DSSCs). The effects of dual-role moieties of organic dyes on their photophysical, electrochemical, and photovoltaic properties have been investigated in detail. These dyes exhibit strong charge transfer absorption bands in the visible region. Their redox potential levels were estimated by cyclic voltammetry and found to suit well to the charge flow in DSSCs. Inserting the dual-role moieties as the secondary donor between the triphenylamine and thiophene units increased the electron density of the donor groups, therefore reduced the HOMO–LUMO band gaps. The combination of ultraviolet–visible (UV–vis) region broad absorption bands with fairly high extinction coefficients and appropriate redox properties observed in these triphenylamine-based dyes make them promising dyes for DSSCs. For a typical solar cell device based on dye SD6, the maximal monochromatic incident photon-to-current conversion efficiency (IPCE) can reach to ∼73%, with a short-circuit photocurrent density ( J sc ) of 14.25 mA/cm 2, an open-circuit photovoltage ( V oc ) of 0.70 V, and a fill factor (FF) of 0.705, which corresponds to a power conversion efficiency (PCE) of 7.03%.

Poly(arylene thioether)s containing 9,9′‐spirobifluorene moieties in the main chain: Masked dithiol‐based synthesis and excellent optical properties

AbstractPoly(arylene thioether)s (PTEs) containing 9,9′‐spirobifluorene moieties were synthesized in high yields from 9,9′‐spirobifluorene‐2,2′‐bis(N,N‐dimethylcarbamothioate) 4 as the masked dithiol and various difluoroarenes as electrophilic monomers. All PTEs showed high thermal stability: The 10% weight loss temperature as evaluated by thermogravimetric analysis was over 470 °C under both nitrogen and air atmospheres. The glass transition temperature estimated by DSC was in the range 210–270 °C. The PTEs showed high solubility in ordinary organic solvents, such as CHCl3, NMP, and THF. Most PTEs exhibited remarkably high refractive indices ranging from 1.69 to 1.73 at 587.6 nm, whereas no or little birefringence was observed for the PTEs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4192–4199, 2010