Spirobifluorene Derivatives Research Articles

Exceptional Field Effect and Negative Differential Conductance in Spiro-Conjugated Single-Molecule Junctions.

The advancement of molecular electronics endeavors to build miniaturized electronic devices using molecules as the key building blocks by harnessing their internal structures and electronic orbitals. To date, linear planar conjugated or cross-conjugated molecules have been extensively employed in the fabrication of single-molecule devices, benefiting from their good conductivity and compatibility with electrode architectures. However, the development of multifunctional single-molecule devices, particularly those with unique charge transport properties, necessitates a more rigorous selection of molecular materials. Among different assortments of molecules suited for the construction of molecular circuits, Spiro-conjugated structures, specifically spirobifluorene derivatives, stand out as promising candidates due to their distinctive electronic properties. In this work, we focus on the charge transport characteristics of Spiro-conjugated molecules sandwiched between graphene nanogaps. Experiments reveal significant Coulomb blockade and distinct negative differential conductance effects. Beyond two-terminal device measurements, solid-state gate electrodes are utilized to create single-molecule transistors, successfully modulating the molecular energy levels to achieve an on/off ratio exceeding 1000. This endeavor not only offers valuable insights into the design and fabrication of future practical molecular devices, blessed with enhanced performance and functionality, but also presents a new paradigm for the investigation of fundamental physical phenomena.

In Situ Thermal Cross-Linking of 9,9'-Spirobifluorene-Based Hole-Transporting Layer for Perovskite Solar Cells.

A novel 9,9'-spirobifluorene derivative bearing thermally cross-linkable vinyl groups (V1382) was developed as a hole-transporting material for perovskite solar cells (PSCs). After thermal cross-linking, a smooth and solvent-resistant three-dimensional (3D) polymeric network is formed such that orthogonal solvents are no longer needed to process subsequent layers. Copolymerizing V1382 with 4,4'-thiobisbenzenethiol (dithiol) lowers the cross-linking temperature to 103 °C via the facile thiol-ene "click" reaction. The effectiveness of the cross-linked V1382/dithiol was demonstrated both as a hole-transporting material in p-i-n and as an interlayer between the perovskite and the hole-transporting layer in n-i-p PSC devices. Both devices exhibit better power conversion efficiencies and operational stability than devices using conventional PTAA or Spiro-OMeTAD hole-transporting materials.

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.

Ring walking as a regioselectivity control element in Pd-catalyzed C-N cross-coupling

Ring walking is an important mechanistic phenomenon leveraged in many catalytic C-C bond forming reactions. However, ring walking has been scarcely studied under Buchwald-Hartwig amination conditions despite the importance of such transformations. An in-depth mechanistic study of the Buchwald-Hartwig amination is presented focussing on ligand effects on ring walking behavior. The ability of palladium catalysts to promote or inhibit ring walking is strongly influenced by the chelating nature of the ligand. In stark contrast, the resting state of the catalyst had no impact on ring walking behavior. Furthermore, the complexity of the targeted system enabled the differentiation between catalysts which undergo ring walking versus diffusion-controlled coupling. The insights gained in this study were leveraged to achieve desymmetrization of a tetrabrominated precursor. A small library of asymmetric 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9’spirobifluorene (SpiroOMeTAD) derivatives were successfully synthesized using this strategy highlighting the ease with which libraries of these compounds can be accessed for screening.

Enhancement of thermoelectric property of carbon nanotubes by p-type doping with judicious molecular design of spiro-bifluorene derivatives

Although thermoelectric composites of carbon nanotubes (CNTs) with organic polymers or small organic molecules have witnessed explosive achievements, judicious molecular design still remains a great challenge. Here, p-type doping using spiro-bifluorene derivatives is proposed to significantly improve single-walled CNT (SWCNT) thermoelectric performance. The composite shows an increase of ∼108% in room-temperature power factor relative to the pristine SWCNT (112.6 ± 4.3 μW m-1 K-2), with the maximum of 239.2 ± 4.2 μW m-1 K-2. The corresponding mechanism of effective p-type doping and strong interfacial interaction are elucidated by calculated energy levels, SWCNT surface coating and photophysical spectroscopic measurements. Finally, the thermoelectric device connected in series display an open-circuit voltage and an output power of 9.77 mV and 57.3 nW, respectively at a temperature gradient of 30 K. The results will benefit the exploitation of novel CNT-based TE composites and their applications.

Inspired from Spiro-OMeTAD: developing ambipolar spirobifluorene derivatives as effective passivation molecules for perovskite solar cells

Accelerated hole extraction efficiency through effective BSBF–NH2 molecule surface passivation.

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.

Application of two spirobifluorene derivatives containing arylamine groups in organic light emitting diodes and fluorescent probe for water

Application of two spirobifluorene derivatives containing arylamine groups in organic light emitting diodes and fluorescent probe for water

Robust tetrakisarylsilyl substituted spirobifluorene: Synthesis and application as universal host for blue to red electrophosphorescence

Stable hosts with high triplet energy levels are of great importance for achieving highly efficient phosphorescence organic light-emitting diodes (PhOLEDs). In this work, a simple and robust spirobifluorene derivative peripherally substituted with tetrakisarylsilyls was designed and synthesized. The spirobifluorene derivative exhibits high thermal/morphological stabilities and ultra-violet blue emissions with moderate fluorescence quantum yields. DFT calculation indicates that the frontier molecular orbitals (FMOs) are mainly associated with the spirobifluorene segment and there is very limited distribution on the peripheral substituents. PhOLEDs using TPSiF as a universal host were fabricated and blue to red emissions were achieved with high efficiencies, among which the green device using Ir(ppy)2acac as guest showed high performance with maximum luminance, current efficiency, power efficiency and external quantum efficiency (EQE) of 11690 cd m−2, 77.2 cd A−1, 47.3 lm W−1, and 21.1%, respectively. Notably, the blue devices show excellent efficiencies at high doping concentration and a 14.9% EQE was achieved at 30 wt % dopant with maximum luminance, current efficiency and power efficiency of 7782 cd m−2, 36.0 cd A−1 and 29.8 lm W−1, respectively.

Fluorescent Sensor for Copper(II) and Cyanide Ions via the Complexation-Decomplexation Mechanism with Di(bissulfonamido)spirobifluorene.

A novel spirobifluorene derivative bearing two bissulfonamido groups is successfully synthesized by Sonogashira coupling. This compound exhibits a strong fluorescence quenching by Cu(II) ion in a 50% mixture between acetonitrile and 20 mM pH 7.0 N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (HEPES) buffer with a detection limit of 98.2 nM. However, this sensor also shows ratiometric signal shifts from blue to yellow in the presence of Zn(II), Pb(II), and Hg(II) ions. The static quenching mechanism is verified by the signal reversibility using ethylenediaminetetraacetic acid (EDTA) and the Stern–Volmer plots at varying temperatures. The Cu(II)–spirobifluorene complex shows a highly selective fluorescence enhancement upon the addition of CN– ion with the detection limit of 390 nM. The application of this complex for quantitative analysis of spiked CN– ion in real water samples resulted in good recoveries.

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.

Correlation between the Intrinsic Photophysical Properties of the Spirobifluorene-Derived Monomer.

Spiro-molecules derived from the functional spirobifluorene core play important roles in the frontiers of diverse optoelectronics. The optoelectronics of these molecules have been intensively studied without yielding a knowledge base of precisely parameterized photophysical properties. Here, we report the precisely parameterized photophysics of spiro-OMeTAD, one prototypical optoelectronic spirobifluorene derivative. The use of a preobtained single-crystalline pure spiro-OMeTAD solid for the solution preparation allows for accurate determination of its molar absorption coefficient (ε) in its monomer form. A near-unity photoluminescence quantum yield (ΦL ∼ 99%) was observed from the monomer solution. The monomer’s photoluminescence decay follows a mono-exponential channel that results in a lifetime (τ) of ∼ 1.64 ns. Taken together ε, ΦL, and τ correlate well via the Strickler–Berg equation. The Strickler–Berg relationship among the key photophysical properties determined on spiro-OMeTAD applies for spirobifluorene derivatives, as verified in an extended test on the newly created spiro-mF. Practical issues that may lead to misparameterized photophysical properties of these molecules are emphasized. Our results of the precisely parameterized photophysical properties of the spiro-OMeTAD monomer in dilute solution serve as background references for studying the optoelectronic processes in the technically more useful thin-film form in practical optoelectronic devices.

Halogen-Bonded Organic Frameworks of Perfluoroiodo- and Perfluorodiiodobenzene with 2,2′,7,7′-Tetrapyridyl-9,9′-spirobifluorene

Single-crystal X-ray diffraction studies on Halogen-Bonded Organic Frameworks (XBOF) formed by N---I contacts of 2,2′,7,7′-tetrapyridyl-9,9′-spirobifluorene with pentafluoroiodobenzene or the isomers of diiodotetrafluorobenzene revealed the formation by F---I, F---F, and I---I halogen bonds of unique tetrameric superstructures of the halogenated derivatives in which the position of I atoms is mimicking the orientation of pyridyl groups in the 9,9′-spirobifluorene derivative resulting in the 1/4 molar ratio coordination of the halogenated compounds to the tetrapyridyl spiro derivative.

Hydrothermal syntheses, structures and properties of a series of new hybrid iodometallates containing rare cross-shaped spirobifluorene derivatives

A series of new hybrid iodometallates [H4Spiro-4-py]n[Cu7I10]n(I3−)n·0.5(I2)n·nH2O (1), [Cu2I2(Spiro-3-py)]n·0.75n(DMF)·0.25nH2O (2), [H2Spiro-4-py][H3Spiro-4-py][Ag10I20]0.5·H2O (3) and [H2Spiro-4-py]n[H3Spiro-4-py]n[Ag8I13]n·2.5H2O (4) were hydrothermal synthesized. 1 contains 1-D chain [Cu7I10]n based on new [Cu7I12] cluster, free I3− anions and I2 molecules, which are interconnected by weak I⋯I interactions to generate a novel polyiodide {[Cu7I10](I3−)·(I2)}n framework. 2 features a neutral sql layer [Cu2I2(Spiro-3-py)]n constructed by the interconnection of the {Cu2I2} dimers and Spiro-3-py ligands. The anionic [Ag10I20]10− framework of 3 can be described as an aggregation of two tetrameric [Ag4I8] clusters and one dimeric [Ag2I6] unit via sharing corner. The 1-D anionic chain [Ag8I135−]n of 4 is built up from the alternate connection of tetrameric [Ag4I8] units and rare larger [Ag12I20] clusters, which offers the only example of 1-D iodoargentates based on two types of iodoargentate clusters. The optical and photoelectronic properties of all compounds were also investigated.

Selective fluorescent sensors for gold(III) ion from N-picolyl sulfonamide spirobifluorene derivatives

Novel spirobifluorene derivatives bearing two and four sulfonamidopicolyl groups were successfully synthesized by Sonogashira couplings. These strongly emissive compounds showed a good selective fluorescent quenching by Au(III) ion in acidic aqueous media solution with three-time-noise detection limits of 9.8 and 86.8 nM. The data from 1H-NMR, UV–vis spectroscopy, and the observation of the Tyndall effect strongly supported a static aggregation-induced quenching mechanism. The application of these sensors for quantitative analysis of spiked Au(III) ion in real water samples from 5 different sources resulted in excellent recoveries.

Structural Diversity Ranging from Oligonuclear Complexes to 1‐D and 2‐D Coordination Polymers Generated by Tetrasubstituted Adamantane and Spirobifluorene Derivatives

Using tetrahedral and tetragonal spacers, seven new complexes have been obtained: [Co(hfac)2(L1)0.5] 1, [Cu2(hfac)4L2] 2, [Co(hfac)2L2] 3, [Co(hfac)2(L2)0.5]·8H2O 4, [AgL2](SbF6)·CH3COOC2H5 5, [Mn(hfac)2(L3)0.5] 6, [Zn(OAc)2(L3)0.5] 7, {L1 = 1,3,5,7‐tetrakis(4‐cyanophenyl)adamantane, L2 = 2,2′,7,7′‐tetracyano‐9,9′‐spirobifluorene and L3 = 2,2′,7,7′‐tetra(4‐pyridyl)‐9,9′‐spirobifluorene, Hhfac = hexafluoroacetylacetone}. Compound 1 exhibits a 2‐D grid‐like structure with the tetradentate spacer acting as a 4‐connecting ligand. The 2,2′,7,7′‐tetrasubstituted‐spirobifluorene derivatives connect the {MII(hfac)2} entities into a binuclear complex (2), a linear chain (3) and diamond chains (4, 6). The cis or trans configuration of the metal nodes influences the overall topology (MII = CuII, CoII, MnII). Similarly, a 1‐D double chain topological motif results by linking zinc ions and L3 in compound 7. Compound 5 is a 2‐D coordination polymer featuring a layered framework with square cavities. Compound 5 undergoes a reversible single‐crystal‐to‐single‐crystal process, with removal of the solvent molecules (ethyl acetate). The luminescence properties of compounds 5, 7 have been investigated and reveal blue emission with maxima at 402 and 483 nm, respectively. The dynamic magnetic properties and EPR spectrum of 1 have been investigated, revealing the occurrence of slow relaxation of the magnetization that most likely involves a Raman process.

Synthesis of Tri- and Disubstituted Fluorenols and Derivatives Thereof Using Catalytic [2+2+2] Cyclotrimerization

A method for regioselective synthesis of 2,4-disubstituted and more highly substituted fluorenols using catalytic [2+2+2]cyclotrimerization of mono- and disubstituted diynes with terminal alkynes was explored. In the former case, the preferential formation of the 2,4-regioisomers was achieved in the presence of Cp*Ru(cod)Cl, whereas Rh-based catalysts tended to provide 3,4-regioisomers as the major products. The 2,4-disubstituted fluorenols were converted into the corresponding 9,9′-spirobifluorene derivatives and their structural and photophysical properties were evaluated.

Spirobifluorene Metallaaromatics.

Spirobifluorene derivatives find use in many end-user applications. Therefore, further expansion of their scope is the focus of many research studies. However, although the optical properties of spirobifluorenes can be greatly tuned through incorporation of metal complexes, to date, spirobifluorene metallaaromatics remain unknown. Taking advantage of the versatility of our methodology for the synthesis of metallaaromatic systems, this work reports the first metallaaromatic spirobifluorene compound. The presence of an Ir atom was found to redshift the absorption maximum by ca. 1.1 eV compared to bare spirobifluorene. Additionally, X-ray analysis as well as anisotropy of the current-induced density calculations revealed this compound to be of aromatic nature. The high stability in solution, solid state, under air, and at high temperature, as well as distinct optical properties of this new class of compounds are expected to open new frontiers for chiroptical and optoelectronic applications.

Theoretical design and simulations of hole transporting materials based on 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene for organic-inorganic hybrid perovskite solar cells

2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene represents one of the most effective hole transporting materials in high efficiency perovskite solar cells. Due to the electronic structural diversity of the perovskite material, 20 spirobifluorene derivatives were designed based on the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene structural template aiming to achieve suitable energy level alignment with perovskite materials that have lower valence band maximums. The designed molecules aim to obtain better absorption spectrum complementation with low-dimensional perovskite materials to eventually get solar cells with ideal efficiencies. The geometry changes caused by different substitutions of diphenylamine groups, the highest occupied molecular orbital energy level regulations by the introduction of nitrogen atoms and methoxy groups on different sites, the reorganization energy variations and the absorption spectra of all the novel structures were carefully predicated and compared with available experimental data. The relationships between the structural variations and the electronic and energy changes are qualitatively and quantitatively discussed.

1-Carbazolyl Spirobifluorene: Synthesis, Structural, Electrochemical, and Photophysical Properties

The present work reports one of the rare examples of a new emerging family of spirobifluorene derivatives, namely, 1-substituted spirobifluorenes. We report the synthesis and the structural, electrochemical, and photophysical properties of 9-(9,9′-spirobi[fluorene]-1-yl)-9H-carbazole 1-Cbz-SBF, constructed from the connection of the widely known electron-rich carbazole fragment at the C1 position of spirobifluorene. We show with 1-Cbz-SBF that the substitution at C1 induces two important characteristics which drive the electronic properties. First, there is a complete π-conjugation breaking between the pending substituent, herein, carbazole, and the substituted fluorene. Second, there is a through-space interaction between the carbazole and its cofacial fluorene. Thanks to a structure–property relationship approach with its constituting building blocks 9,9′-spirobifluorene SBF and carbazole Cbz, we show how some electronic properties are driven by the carbazole unit such as the highest occupied molecular ...