Spiro Compounds for Organic Electroluminescence and Related Applications

Crafting 1,4-diaryl spirobifluorene hosts in OLEDs via interannular C-H arylation: synergistic effects of molecular linearity and orthogonality

In this work, we present a design concept of introducing linear structures into the orthogonal configuration of 9,9'-spirobifluorene (SBF), aiming to enhance carrier mobilities while maintaining high triplet energies (E T), which are two critical parameters for optimizing host materials in organic light-emitting diodes (OLEDs). To validate our proposed design, four pivotal model molecules of 1,4-diaryl SBFs were synthesized via interannular C-H arylation of bi(hetero)aryl-2-formaldehydes, a task challenging to accomplish using previous synthetic methodologies. The orthogonal configuration and the steric hindrance of SBF lead to high E T through the conjugation breaking at C1 and C4 positions, rendering 1,4-diaryl SBFs suitable as universal pure hydrocarbon (PHC) hosts for red, green, and blue (RGB) phosphorescent OLEDs (PhOLEDs). Meanwhile, the linearity and relatively good planarity of the para-quaterphenyl structure promote high carrier mobilities through orderly intermolecular packing. The synergistic effects of linearity and orthogonality in 1-(para-biphenyl)-4-phenyl-SBF result in exceptional device performance with external quantum efficiencies (EQEs) of 26.0%, 26.1%, and 22.5% for RGB PhOLEDs, respectively. Notably, the green PhOLED exhibits minimal efficiency roll-off, positioning its device performances among the state-of-the-art in PHC hosts.

Construction of Annulated Spiro[4.4]-nonane-diones via the Tandem [4 + 2]-Cycloaddition/Aromatization Reaction

A method for the synthesis of both symmetric and asymmetric fused spiro[4.4]-nonane-dione derivatives has been developed. It is based on a Diels-Alder reaction of spiro[4.4]nona-2,7-diene-1,6-dione as a dienophile component followed by immediate aromatization of the adduct. An active diene component can be generated using the tetrabromoxylene/NaI system, the 1,3-diphenylisobenzofuran/BF3 system, or substituted cyclones.

Symmetry-Breaking Induced Dipole Enhancement for Efficient Spiro-Type Hole Transporting Materials: Easy Synthesis with High Stability

Spiral cores are crucial for designing efficient hole transporting materials (HTMs) for perovskite solar cells (PSCs), owing to their no-planar 3D architecture, high thermal stability, good solubility, and beneficial solid-state morphology. A lack of facile synthetic procedures for the spiral core limited the development of novel and stable spiral HTMs. In this regard, a one-step reaction is adopted to produce several novel acceptor-embedded spiral cores containing electron-withdrawing carbonyl group embedded orthogonal spiral conformation. After coupling with triphenylamine donors, symmetry-breaking spiral HTMs with uneven charge distribution can be obtained, bearing the advantages of adjustable dipole moment and enhanced structural stability. A combined theoretical and experimental study shows that the HTM with a stronger dipole moment can easily adsorb on the surface of perovskite via electrostatic potential, and the closer distance promoted facile hole transfer from perovskite to HTMs. In the end, PSCs based on strongly polarized spiro-BC-OMe achieved efficient hole extraction and thus an improved fill factor, promoting a power conversion efficiency (PCE) of 22.15%, and a module-based PCE of 18.61% with an active area of 16.38 cm² . This study provides a new avenue for designing HTMs with strong dipole moments for efficient PSCs.

Pure Hydrocarbon Materials as Highly Efficient Host for White Phosphorescent Organic Light-Emitting Diodes: A New Molecular Design Approach

To date, all efficient host materials reported for phosphorescent OLEDs (PhOLEDs) are constructed with heteroatoms, which have a crucial role in the device performance. However, it has been shown in recent years that the heteroatoms not only increase the design complexity but can also be involved in the instability of the PhOLED, which is nowadays the most important obstacle to overcome. Herein, we design pure aromatic hydrocarbon materials (PHC) as very efficient hosts in high-performance white and blue PhOLEDs. With EQE of 27.7 %, the PHC-based white PhOLEDs display similar efficiency as the best reported with heteroatom-based hosts. Incorporated as a host in a blue PhOLED, which are still the weakest links of the technology, a very high EQE of 25.6 % is reached, surpassing, for the first time, the barrier of 25 % for a PHC and FIrpic blue emitter. This performance shows that the PHC strategy represents an effective alternative for the future development of the OLED industry.

Furan-Containing Chiral Spiro-Fused Polycyclic Aromatic Compounds: Synthesis and Photophysical Properties

Spiro-fused polycyclic aromatic compounds (PACs) have received growing interest as rigid chiral scaffolds. However, furan-containing spiro-fused PACs have been quite limited. Here, we design spiro[indeno[1,2-b][1]benzofuran-10,10′-indeno[1,2-b][1]benzothiophene] as a new family of spiro-fused PACs that contains a furan unit. The compound was successfully synthesized in enantiopure form and also transformed to its S,S-dioxide derivative and the pyrrole-containing analog via aromatic metamorphosis. The absorption and emission properties of the obtained furan-containing chiral spiro-fused PACs are apparently different from those of their thiophene analogs that have been reported, owing to the increased electron-richness of furan compared to thiophene. All of the furan-containing chiral spiro-fused PACs were found to be circularly polarized luminescent materials.

Challenges for Thermally Stable Spiro-MeOTAD toward the Market Entry of Highly Efficient Perovskite Solar Cells

Perovskite solar cells (PSCs) have drawn great attention because they have seen a dramatic increase in power conversion efficiency (PCE) over only a decade and reached 25.5% of certified PCE in 2021. The efficiency competitiveness with a low production cost puts up PSCs as a candidate for next-generation photovoltaics, encouraging the stability assessment. Research on PSCs, however, still struggles with the stability issue, particularly at elevated temperature, which is mainly ascribed to the use of spiro-MeOTAD as a hole transport material (HTM). Though many attempts have been made to explore a new HTM to replace spiro-MeOTAD, the improved stability is mostly obtained at the expense of losing efficiency. Likewise, the question of the effectiveness of alternatives for spiro-MeOTAD consistently remains. In this perspective, the morphological stability of spiro-MeOTAD at elevated temperatures is discussed to determine the underlying origins of the thermal stability issue and find feasible strategies to resolve it.

1H-Pyrazolo[3,4-b]quinolines: Synthesis and Properties over 100 Years of Research

This paper summarises a little over 100 years of research on the synthesis and the photophysical and biological properties of 1H-pyrazolo[3,4-b]quinolines that was published in the years 1911–2021. The main methods of synthesis are described, which include Friedländer condensation, synthesis from anthranilic acid derivatives, multicomponent synthesis and others. The use of this class of compounds as potential fluorescent sensors and biologically active compounds is shown. This review intends to summarize the abovementioned aspects of 1H-pyrazolo[3,4-b]quinoline chemistry. Some of the results that are presented in this publication come from the laboratories of the authors of this review.

Cu-Catalyzed synthesis of spiroimidazole derivatives via an indolyl mediated cyclization–rearrangement reaction

A novel Cu-catalyzed synthesis of structurally valuable spiroimidazole derivatives from 2-(indol-3-yl)cyclohexanones and amidines via an indolyl mediated cyclization–rearrangement reaction is described.

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.

All-nitrogen spiropentadiene-N5. J Chem Phys 2021;155:174304. [PMID: 34742197 DOI: 10.1063/5.0070369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Of the pentanitrogen cation (N₅ ⁺) family, the only experimentally known isomer is the V-shaped structure 01. Here, we showed that a super-high-energy (∼100 kcal/mol above 01) all-nitrogen spiropentadiene 02 with considerable σ-delocalization deserves pursuit as the first spirocyclic all-nitrogen molecule, at least spectroscopical.

Solvent-sensitive circularly polarized luminescent compounds bearing a 9,9′-spirobi[fluorene] skeleton

Chiral 9,9′-spirobi[fluorene] derivatives with a donor–π–acceptor system were prepared and found to exhibit solvent-sensitive circularly polarized luminescence.

Facile Synthesis of 2,2-Diacyl Spirocyclohexanones via an N-Heterocyclic Carbene-Catalyzed Formal [3C + 3C] Annulation

A novel strategy for the construction of 2,2-diacyl spirocyclohexanones 3 has been demonstrated on the basis of an NHC-catalyzed [3C + 3C] annulation of potassium 2-oxo-3-enoates with 2-ethylidene 1,3-indandiones. Furthermore, enantioenriched 3 was obtained in good to excellent yields with good enantioselectivities when chiral N-heterocyclic carbene (NHC) was employed. Notably, ring opening of the resulting 2,2-diacyl spirocyclohexanones 3 with hydrazine led to the formation of phthalazinones in good to excellent yields.

Photoinduced dynamics in cycloparaphenylenes: planarization, electron–phonon coupling, localization and intra-ring migration of the electronic excitation

Cycloparaphenylenes represent the smallest possible fragments of armchair carbon nanotubes.

Hydrophobic Organic Hole Transporters for Improved Moisture Resistance in Metal Halide Perovskite Solar Cells

Solar cells based on organic-inorganic perovskite semiconductor materials have recently made rapid improvements in performance, with the best cells performing at over 20% efficiency. With such rapid progress, questions such as cost and solar cell stability are becoming increasingly important to address if this new technology is to reach commercial deployment. The moisture sensitivity of commonly used organic-inorganic metal halide perovskites has especially raised concerns. Here, we demonstrate that the hygroscopic lithium salt commonly used as a dopant for the hole transport material in perovskite solar cells makes the top layer of the devices hydrophilic and causes the solar cells to rapidly degrade in the presence of moisture. By using novel, low cost, and hydrophobic hole transporters in conjunction with a doping method incorporating a preoxidized salt of the respective hole transporters, we are able to prepare efficient perovskite solar cells with greatly enhanced water resistance.

Synthesis of poly(spirosilabifluorene) copolymers and their improved stability in blue emitting polymer LEDs over non-spiro analogs

PHSSF-co-PDHSF exhibits blue luminescence, high quantum efficiency and thermal stability. Electroluminescence of OLEDs is more stable than non-spiro poly(silafluorene) devices.

meta-Chloroperbenzoic acid (mCPBA): a versatile reagent in organic synthesis

This review aims to collect and discuss the synthetic applications of meta-chloroperbenzoic acid (mCPBA) over the past few decades.