Hole-Transporting Materials based on Oligo(hetero)aryls with a Naphthodithiophene Core - Succinct Synthesis by Twofold Direct C-H Olefination.

This work demonstrated the first synthetic application of direct C-H olefinations in the step-saving preparation of various hole-transporting materials (HTM) for efficient perovskite solar cells (PSC). Cross-dehydrogenative couplings of naphthodithiophene (NDT) with vinyl arenes under palladium-catalysis facilely generated various new oligo(hetero)aryls with internal alkenes. Reaction conditions were optimized, which gave the product isolated yields of up to 71 % with high (E)-stereoselectivity. These readily accessible NDT core-based small molecules involving olefin as π-spacers displayed immediate power conversion efficiencies of up to 17.2 % without a device oxidation process that is required for the commercially available spiro-OMeTAD and most other existing HTMs while fabricated in corresponding PSC devices.

New Molecular Design, Step-Saving Synthesis, and Applications of Indolocarbazole Core-Based Oligo(hetero)arenes.

In this work, we have successfully synthesized 15 new examples (LLA01-06; LinLi01-10) of small-molecule hole-transporting materials (HTM) using the less explored indolocarbazole (ICbz) as core moiety. Different from previously reported ICbz HTMs, LinLi01-10 exhibit new molecular designs in which 3,4-ethylenedioxythiophene (EDOT) units are inserted as crucial π-spacers and fluorine atoms are introdcued into end-group molecules. These substantially improve the materials solubility and device power conversion efficiencies (PCEs) while fabricated in perovskite solar cells (PSC). More importantly, LinLi01-10 are generated by a sustainable synthetic approach involving the use of straightforward C-H/C-Br couplings as key transformations, thus avoiding additional synthetic transformations including halogenation and borylation reactions called substrate prefunctionalizations usually required in Suzuki reactions. Most HTM molecules can be purified simply by reprecipitations instead of conducting column chromatography. In contrast to LLA01-06 without additional EDOT moieties, PSC devices using LinLi01-10 as hole-transport layers display promising PCEs of up to 17.5 %. Interestingly, PSC devices employing seven of the LinLi01-10 as hole-transport molecules, respectively, are all able to show an immediate >10 % PCE (t=0) without any device oxidation/aging process that is necessary for the commercial spiro-OMeTAD based PSCs.

Surfactant Tween 20 Controlled Perovskite Film Fabricated by Thermal Blade Coating for Efficient Perovskite Solar Cells.

In recent years, additive engineering has received considerable attention for the fabrication of high-performance perovskite solar cells (PSCs). In this study, a non-ionic surfactant, polyoxyethylene (20) sorbitan monolaurate (Tween 20), was added as an additive into the MAPbI3 perovskite layer, and the thermal-assisted blade-coating method was used to fabricate a high-quality perovskite film. The Tween 20 effectively passivated defects and traps in the MAPbI3 perovskite films. Such a film fabricated with an appropriate amount of Tween 20 on the substrate showed a higher photoluminescence (PL) intensity and longer carrier lifetime. At the optimal concentration of 1.0 mM Tween 20, the performance of the PSC was apparently enhanced, and the champion PSC demonstrated a PCE of 18.80%. Finally, this study further explored and compared the effect on the device performance and ambient stability of the MAPbI3 perovskite film prepared by the spin-coating method and the thermal-assisted blade coating.

Reducing Defects in Organic-Lead Halide Perovskite Film by Delayed Thermal Annealing Combined with KI/I2 for Efficient Perovskite Solar Cells.

This study improved quality of CH3NH3PbI3 (MAPbI3) perovskite films by delaying thermal annealing in the spin coating process and introducing KI and I2 to prepare MAPbI3 films that were low in defects for high-efficiency perovskite solar cells. The influences of delayed thermal annealing time after coating the MAPbI3 perovskite layer on the crystallized perovskite, the morphology control of MAPbI3 films, and the photoelectric conversion efficiency of solar cells were investigated. The optimal delayed thermal annealing time was found to be 60 min at room temperature. The effect of KI/I2 additives on the growth of MAPbI3 films and the corresponding optimal delayed thermal annealing time were further investigated. The addition of KI/I2 can improve perovskite crystallinity, and the conductivity and carrier mobility of MAPbI3 films. Under optimized conditions, the photoelectric conversion efficiency of MAPbI3 perovskite solar cells can reach 19.36% under standard AM1.5G solar illumination of 100 mW/cm2.

Development of Step-Saving Alternative Synthetic Pathways for Functional π-Conjugated Materials.

Synthetic organic chemists endeavor to develop new reaction conditions, improve product yields, and enhance atom economy (synthetic methodologies), whereas the material scientists strive to create novel functional molecules/structures, increase device stabilities, and promote power conversion efficiencies via device engineering (organic optoelectronics). However, these two prominent research fields seem to have no intersections. Since joining national central university in 2012, our research philosophy aims to narrow, or rather to bridge the gap between synthetic methodologies and π-functional organic materials. In contrast to using multistep synthetic approaches based on Suzuki- or Stille coupling reactions, this personal account describes various step-saving and viable synthesis-shortcuts developed by our group, to access thiophene-based small molecules for optoelectronic applications. We expect these succinct and user-friendly alternative pathways designed by synthetic chemists would help material scientists to reach their target molecules in a more step-economical manner.

Step-saving synthesis of star-shaped hole-transporting materials with carbazole or phenothiazine cores via optimized C-H/C-Br coupling reactions.

In most research papers, synthesis of organic hole-transporting materials relies on a key-reaction: Stille cross-couplings. This requires tedious prefunctionalizations including the preparation and treatment of unstable organolithium and toxicity-concern organotin reagents. In contrast to traditional multistep synthesis, this work describes that a series of star-shaped small molecules with a carbazole or phenothiazine core can be efficiently synthesized through a shortcut using optimized direct C-H/C-Br cross-couplings as the key step, thus avoiding dealing with the highly reactive organolithium or the toxic organotin species. Device fabrication of perovskite solar cells employing these molecules (6-13) as hole-transporting layers exhibit promising power conversion efficiencies of up to 17.57%.

One-pot synthesis of D-π-D-π-D type hole-transporting materials for perovskite solar cells by sequential C-H (hetero)arylations.

We report a step-saving new access to D-π-D-π-D type oligoaryls through one-pot sequential C-H (hetero)arylations. Conventionally, these oligomers were prepared by Stille or Suzuki coupling reactions that required prefunctionalization steps. The facilely synthesized linear oligomers were fabricated in perovskite-based solar devices as efficient hole transporters, exhibiting a power conversion efficiency of up to 15.4%.

Direct C-H Arylation Meets Perovskite Solar Cells: Tin-Free Synthesis Shortcut to High-Performance Hole-Transporting Materials.

In contrast to the traditional multistep synthesis, we demonstrate herein a two-step synthesis shortcut to triphenylamine-based hole-transporting materials (HTMs) through sequential direct C-H arylations. These hole-transporting molecules are fabricated in perovskite-based solar cells (PSCs) that exhibit promising efficiencies up to 17.69 %, which is comparable to PSCs utilizing commercially available 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD) as the HTM. This is the first report describing the use of step-saving C-H activations/arylations in the facile synthesis of small-molecule HTMs for perovskite solar cells.

Sn- and Pd-Free Synthesis of D-π-A Organic Sensitizers for Dye-Sensitized Solar Cells by Cu-Catalyzed Direct Arylation.

Cross-Dehydrogenative Coupling (CDC) as Key-Transformations to Various D-π-A Organic Dyes: C-H/C-H Synthetic Study Directed toward Dye-Sensitized Solar Cells Applications.

A variety of push-pull type organic dyes are facilely synthesized through the most atom-economical C-H/C-H dehydrogenative coupling reactions. After comprehensive synthetic optimizations, a broad substrate scope is achieved and functional groups, such as ester, ketone, nitrile, nitro, and triazene are well tolerated. The sensitive aldehyde group required for the conversion into anchoring groups for DSSCs applications is also compatible under present oxidant-containing reaction conditions. Based on this optimum C-H/C-H coupling approach, three new organic sensitizers are readily prepared and submitted to solar cell device fabrications, giving the power conversion efficiency (PCE) up to 4.85%. This work constitutes the first example that connects high atom-efficiency C-H/C-H green catalysis with dye-sensitized solar cell applications.

Proliferation and osteogenic differentiation of amniotic fluid-derived stem cells.

Human amniotic fluid-derived stem cells (hAFCs) are pluripotent fetal cells capable of differentiating into multiple lineages, including cell types of each of the three embryonic germ layers. Proper differentiation and maintenance of pluripotency, the defining characteristics of stem cells, are regulated not only by the cells themselves but also by their microenvironment. Furthermore, the physical characteristics of the cell culture materials, such as material elasticity, influence the results of stem cell differentiation. We investigated the osteogenic differentiation efficiency of hAFCs cultured on cell culture materials with different elasticities that were grafted with extracellular matrix-derived oligopeptides. Polyvinyl alcohol-co-itaconic acid (PV) hydrogels with different elasticities were prepared by controlling the crosslinking intensity, and the resulting PV hydrogels were grafted with and without extracellular matrix (ECM)-derived oligopeptides. Specific ECM-derived oligopeptides were used to maintain the pluripotency of AFCs and were determined by evaluation of pluripotent gene expression (Sox2 and Oct4). The osteogenic differentiation efficiency of the hAFCs, cultured on PV hydrogels grafted with and without ECM-derived oligopeptides, was analyzed by alkaline phosphatase activity, Alizarin Red S staining, and von Kossa staining. Unmodified PV hydrogels induced osteoblast differentiation of hAFCs with high efficiency. We conclude that the hAFCs interacting with ECM-derived oligopeptides tended to maintain an undifferentiated state.

Connecting Direct C-H Arylation Reactions with Dye-Sensitized Solar Cells: A Shortcut to D-A-π-A Organic Dyes.

A step-economical synthetic strategy is developed to target thieno[3,4-c]pyrrole-4,6-dione (TPD)-based D-A-π-A organic dyes for dye-sensitized solar cells (DSSCs). Through sequential Pd-catalyzed direct C-H (hetero)arylation reaction, synthesis of the push-pull-type small molecules is reduced from the traditional six steps to two steps. In this report, we focus on the optimization of the key C-H monoarylation of TPD by screening ligands, acid additives, bases, and solvents. The reaction proves versatile toward new D-A-π-A organic dyes with a variety of different donor groups, and several derivatives are efficiently prepared under optimum reaction conditions. The sensitive aldehyde functionality that is a required intermediate for conversion into anchoring groups for TiO2 is well tolerated. Based on our synthetic study, DSSCs are fabricated and characterized using two designed sensitizers. The photovoltaic characterization of the devices affords an open-circuit voltage of 0.60-0.69 V, a short-circuit current density of 10.85-11.07 mA cm(-2), and a fill factor of 69.9-70.8 %, which corresponds to an overall power conversion efficiency of 4.61-5.33 %.

Palladium-catalyzed direct C-H arylations of dioxythiophenes bearing reactive functional groups: a step-economical approach for functional π-conjugated oligoarenes.

A Pd-catalyzed single-step C-H arylation of dioxythiophene derivatives bearing unprotected reactive functional groups (-OH, -COOH, -N3) in a phosphine-free manner has been developed. Various dioxythiopene-based oligoarenes with extended π-conjugation are obtained with good yields (up to 90%). These oligoarenes display suitable optical properties (absorption and emission maxima, quantum yields) and contain reactive functional groups suitable for further conjugations with bioactive molecules. This new methodology is step economical (fewer synthetic steps) and environmentally friendly (no toxic metal-containing by-products) and the oligoarenes synthesized are potentially applicable for bio-labeling, bioimaging, and biosensing.

Step-Economical Syntheses of Functional BODIPY-EDOT π-Conjugated Materials through Direct C-H Arylation.

Palladium-catalyzed direct C-H arylations of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) with 3,4-ethylenedioxythiophene (EDOT) derivatives at relatively low temperature (60 °C) provide moderate to good yields (47%-72%) of products having potential applications in fluorescent bioimaging and organic optoelectronics.

From-core and from-end direct C-H arylations: a step-saving new synthetic route to thieno[3,4-c]pyrrole-4,6-dione (TPD)-incorporated D--π-A-π-D functional oligoaryls.

In contrast to the traditional multistep synthesis, herein an efficient and fewer-steps new synthetic strategy is demonstrated for the facile preparation of organic-electronically important D-π-A-π-D-type oligoaryls through sequential direct CH arylations. This methodology has shown that the synthesis of thieno[3,4-c]pyrrole-4,6-dione (TPD)- or furano[3,4-c]pyrrole-4,6-dione (FPD)-centred target molecules could be accessed step-economically either from the core structure (acceptor) or from the end structure (donor), which supplied a more flexible and succinct new synthetic alternative to the preparation of the π-functional small-molecule semiconducting materials. In addition, optical and electrochemical properties of the synthesized oligoaryls were examined.

Efficient synthesis of 3,4-ethylenedioxythiophene (EDOT)-based functional π-conjugated molecules through direct C-H bond arylations.

A variety of 3,4-ethylenedioxythiophene (EDOT)-based π-conjugated molecules were efficiently synthesized in good yields through Pd-catalyzed direct C-H bond arylations, wherein a detailed synthetic investigation, including the screening of various kinds of palladium catalysts, ligands, additives, and solvents, was carried out. In addition, the spectroscopic and electrochemical properties of these EDOT-containing molecules were also investigated.

Theoretical study on the halogen-zinc exchange reaction by using organozincate compounds.

Density functional theory (DFT) calculations have been performed to examine the mechanism of the halogen-zinc exchange reaction of organozincate reagents (Me(2)RZnLi x OMe(2); R = Me, Et, iPr, and tBu) with organohalides (RX; R = Me, vinyl, ethynyl, -CH(Cl)CH(3), -CH(CH(3))CHCH(2); X = Cl, Br, I). We focused on three areas: 1) the effect of the halogen species, 2) the effect of the alkyl ligand on zinc, 3) the effect of the substrate nature. Fragment-energy analysis of each reaction was conducted to elucidate the factors determining the activation energy. The nature of the halogen atom affects the interaction (INT) energy but does not affect the deformation (DEF) energy. On the other hand, the type of alkyl ligand influences DEF rather than INT and bulky ligands (including tert-butyl and iso-propyl groups) decrease the activation energy compared with smaller ligands, such as ethyl and methyl groups. In the reaction with vinyl iodide, a decrease in DEF promoted the reaction, whereas INT was almost unchanged. However, in the case of iodoacetylene, a decrease in INT lowered the activation energy. For allyl iodide derivatives DEF appears to be the determining factor, whereas for gem-dihaloalkane derivatives INT is the main determinant of reactivity.

Effect of periodic replacement of the heteroatom on the spectroscopic properties of indole and benzofuran derivatives.

The electronic structures of a homologous series of indole and benzofuran derivatives, in which the nitrogen or oxygen atom is replaced by group 15 and group 16 heavier heteroatoms, have been investigated by means of various spectroscopic techniques coupled with density functional calculations. It was found that the excitation energies of the group 16 benzoheteroles systematically shift to the red in the order of benzofuran (6), benzothiophene (7), benzoselenophene (8), and benzotellurophene (9). In contrast, the electronic absorption spectra of the group 15 benzoheteroles, 1-phenyl derivatives of indole (1b), phosphindole (2b), arsindole (3b), stibindole (4b), and bismuindole (5b), did not exhibit this type of spectral shift. X-ray analysis and density functional theory (DFT) studies revealed that 2b-5b adopt a bent conformation both in the crystalline and in the solution phases. In contrast, planar structures were calculated for the group 16 heterocycles. Using the observed spectroscopic properties and time-dependent density functional theory (TDDFT) calculations, the electronic absorption spectra of the present heterocycles were assigned. A molecular orbital analysis was performed to rationalize the effect of replacement of the heteroatom on the electronic structures. The observed magnetic circular dichroism (MCD) sign patterns of these heterocycles are interpreted according to Michl's perimeter model.