Facile Synthesis of Spirooxindole‐Cyclohexenes via Phosphine‐Catalyzed [4 + 2] Annulation of α‐Substituted Allenoates

A phosphine‐catalyzed [4 + 2] annulation of α ‐substituted allenoate with exocyclic alkene moiety of oxindoles or indan‐1,3‐diones has been developed. Thus, under the catalysis of PPh₃ (20 mol%), a series of spirooxindole‐ or spiroindan‐1,3‐dione‐cyclohexenes have been obtained in moderate to excellent yields and regioselectivity from the annulations of α ‐methyl allenoates with 3‐methyleneoxindoles or 2‐methyleneindan‐1,3‐diones. This method offers an easy access to structurally novel spirocyclohexenes.     

Donor–Acceptor (D–A)‐Substituted Polyyne Chromophores: Modulation of Their Optoelectronic Properties by Varying the Length of the Acetylene Spacer

A series of donor–acceptor‐substituted alkynes, 2 a – f , was synthesized in which the length of the π‐conjugated polyyne spacer between the N,N‐diisopropylanilino donor and the 1,1,4,4‐tetracyanobuta‐1,3‐diene (TCBD) acceptor was systematically changed. The effect of this structural change on the optoelectronic properties of the molecules and, ultimately, their third‐order optical nonlinearity was comprehensively investigated. The branched N,N‐diisopropyl groups on the anilino donor moieties combined with the nonplanar geometry of 2 a – f imparted exceptionally high solubility to these chromophores. This important property allowed for performing INADEQUATE NMR measurements without ¹³C labeling, which, in turn, resulted in a complete assignment of the carbon skeleton in chromophores 2 a – f and the determination of the ¹³C–¹³C coupling constants. This body of data provided unprecedented insight into characteristic ¹³C chemical shift patterns in push–pull‐substituted polyynes. Electrochemical and UV/Vis spectroscopic studies showed that the HOMO–LUMO energy gap decreases with increasing length of the polyyne spacer, while this effect levels off for spacers with more than four acetylene units. The third‐order optical nonlinearity of this series of molecules was determined by measuring the rotational averages of the third‐order polarizabilities (γ_rot) by degenerate four‐wave mixing (DFWM). These latter studies revealed high third‐order optical nonlinearities for the new chromophores; most importantly, they provided fundamental insight into the effect of the conjugated spacer length in D–A polyynes, that can be exploited in the future design of suitable charge‐transfer chromophores for applications in optoelectronic devices.     

An Efficient Route for the Synthesis of 11‐Aroyldiindeno[1,2‐b:2′,1′‐e]pyridine‐10,12‐diones

A series of novel 11‐aroyldiindeno[1,2‐b :2′,1′‐e ]pyridine‐10,12‐dione derivatives were synthesized, in good to excellent yields and short reaction times via one‐pot, three‐component reactions between indan‐1,3‐dione, ammonium acetate, and arylglyoxal hydrates in the presence of solid p ‐toluenesulfonic acid.     

Alphabet‐Inspired Design of (Hetero)Aromatic Push–Pull Chromophores

Push–pull molecules represent a unique and fascinating class of organic π‐conjugated materials. Herein, we provide a summary of their recent extraordinary design inspired by letters of the alphabet, especially focusing on H‐, L‐, T‐, V‐, X‐, and Y‐shaped molecules. Representative structures from each class were presented and their fundamental properties and prospective applications were discussed. In particular, emphasis is given to molecules recently prepared in our laboratory with T‐, X‐, and Y‐shaped arrangements based on indan‐1,3‐dione, benzene, pyridine, pyrazine, imidazole, and triphenylamine. These push–pull molecules turned out to be very efficient charge‐transfer chromophores with tunable properties suitable for second‐order nonlinear optics, two‐photon absorption, reversible pH‐induced and photochromic switching, photocatalysis, and intercalation.

     

Regioselective Synthesis of Fused Azo‐linked Pyrazolo[4,3‐e]pyridines Using Nano‐Fe3O4

A multicomponent reaction for the synthesis of fused azo‐linked pyrazolo[4,3‐e]pyridines from 3‐amino‐5‐methylpyrazole, indan‐1,3‐dione and synthesized azo‐linked aldehydes using nano‐Fe₃O₄ as an effective and reusable catalyst is reported. The present methodology offers several advantages, such as a simple procedure with an easy work‐up, short reaction times, high yields, and the absence of any volatile and hazardous organic solvents.     

Diels–Alder reaction of 2,7‐dichloroquinoline‐5,8‐dione with a thiazole o‐quinodimethane. Assignment of the regiochemistry by 1H–13C HMBC correlations

The Diels–Alder reaction between a thiazole o‐quinodimethane and 4,6‐dichloroquinoline‐5,8‐dione gave 6‐chloro‐9‐azaanthra[2,3‐b]thiazole‐5,10‐dione as a single regioisomer. Its structure was assigned by 2D ¹H–¹³C HMBC short‐ and long‐range correlations. Measuring the spectra in CF₃CO₂D indicated that both nitrogen atoms of pyridine and thiazole rings are deuterated. Copyright © 2001 John Wiley & Sons, Ltd.     

A New and Convenient Synthesis of Amino‐phthalimide (1H‐Isoindole‐1,3(2H)‐dione) Derivatives and Their Photoluminescent Properties

A new and convenient synthesis for amino‐phthalimide (1H‐isoindole‐1,3(2H)‐dione) derivatives has been developed starting from an α,β‐unsaturated ketone. The ketones were reacted with amines to give aromatic amine products. This is the first time that substituted amine groups have been incorporated in aromatic rings. The mechanism of the product formation is rationalized by the 1,2‐addition of amines to ketones. All aromatic compounds exhibited high fluorescence properties at the blue‐green region.     

One‐pot,fast cyclopropanation reaction of indandione with various aldehydes in the presence of cyanogen bromide and trimethylamine

A new, fast, and easy one‐pot cyclopropanation reaction of aromatic and aliphatic aldehydes with 1H‐indene‐1,3(2H)‐dione and cyanogen bromide (BrCN) was developed for synthesizing 3′‐(aryl[alkyl])‐dispiro[indan‐2,1′‐cyclopropane‐2′,2′′‐indan]‐1,1′′,3,3′′‐tetrone in excellent yields in a short time (about 15 s) under basic media. All structures were characterized using IR, ¹H NMR, and ¹³C NMR spectroscopy techniques.     

Donor–acceptor photovoltaic polymers based on 1,4‐dithienyl‐2,5‐dialkoxybenzene with intramolecular noncovalent interactions

Donor–acceptor (D–A) conjugated polymers bearing non‐covalent configurationally locked backbones have a high potential to be good photovoltaic materials. Since 1,4‐dithienyl‐2,5‐dialkoxybenzene ( TBT ) is a typical moiety possessing intramolecular S…O interactions and thus a restricted planar configuration, it was used in this work as an electron‐donating unit to combine with the following electron‐accepting units: 3‐fluorothieno[3,4‐b]thiophene ( TFT ), thieno‐[3,4‐c]pyrrole‐4,6‐dione ( TPD ), and diketopyrrolopyrrole ( DPP ) for the construction of such D–A conjugated polymers. Therefore, the so‐designed three polymers, PTBTTFT , PTBTTPD , and PTBTDPP , were synthesized and investigated on their basic optoelectronic properties in detail. Moreover, using [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as acceptor material, polymer solar cells (PSCs) were fabricated for studying photovoltaic performances of these polymers. It was found that the optimized PTBTTPD cell gave the best performance with a power conversion efficiency (PCE) of 4.49%, while that of PTBTTFT displayed the poorest one (PCE = 1.96%). The good photovoltaic behaviors of PTBTTPD come from its lowest‐lying energy level of the highest occupied molecular orbital (HOMO) among the three polymers, and good hole mobility and favorable morphology for its PC₇₁BM‐blended film. Although PTBTDPP displayed the widest absorption spectrum, the largest hole mobility, and regular chain packing structure when blended with PC₇₁BM, its unmatched HOMO energy level and disfavored blend film morphology finally limited its solar cell performance to a moderate level (PCE: 3.91%). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 689–698     

Photoluminescent properties of poly(p‐phenylene vinylene thiophene‐co‐siloxane)

A new p‐phenylene–vinylene–thiophene‐based siloxane block copolymer has been synthesized. The copolymer consists of alternating rigid and flexible blocks. The rigid blocks are composed of phenylene–vinylene–thiophene‐based units, and the flexible blocks are derived from 1,3‐dialkyldisiloxane units. The former component acts as the chromophore, and allows fine tuning of band gap for blue‐light emission, while the latter imparts good solubility of the copolymer in organic solvents, and thus, should enhance processibility of the resulting copolymer. The thermal properties of the copolymer have been characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The photoluminescence (PL) of the copolymer in solution and in cast film has been studied. The effects of concentration on the PL intensity of the new copolymer in polymer blends with poly(methyl methacrylate) (PMMA) and poly(vinyl carbazole) (PVK) have also been described. Efficient energy transfer from PVK to the new block copolymer in the blended film was observed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1450–1456, 2000     

Synthesis and Photovoltaic Properties of Thieno[3,4‐c]pyrrole‐4,6‐dione‐based donor–acceptor Copolymers

Three donor–acceptor (D–A) 1,3‐di(thien‐2‐yl)thieno [3,4‐c]pyrrole‐4,6‐dione‐based copolymers, poly{9,9‐dioctylfluorene‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, poly{N‐(1‐octylnonyl)carbazole‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, and poly {4,8‐bis(2‐ethylhexyloxyl) benzo[1,2‐b:3,4‐b′]dithiophene‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c] pyrrole‐4,6‐dione} were synthesized by Suzuki or Stille coupling reaction. By changing the donor segment, the bandgaps and energy levels of these copolymers could be finely tuned. Cyclic voltammetric study shows that the highest occupied molecular orbital (HOMO) energy levels of the three copolymers are deep‐lying, which implies that these copolymers have good stability in the air and the relatively low HOMO energy level assures a higher open‐circuit potential when they are used in photovoltaic cells. Bulk‐heterojunction photovoltaic cells were fabricated with these polymers as the donors and PC₇₁BM as the acceptor. The cells based on the three copolymers exhibited power conversion efficiencies of 0.22, 0.74, and 3.11% with large open‐circuit potential of 1.01, 0.99, and 0.90 V under one sun of AM 1.5 solar simulator illumination (100 mW/cm²). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A New Four‐Component Reaction for the Synthesis of Spiro[4H‐indeno[1,2‐b]pyridine‐4,3′‐[3H]indoles]

A new four‐component synthesis of spiro[4H‐indeno[1,2‐b]pyridine‐4,3′‐[3H]indoles] and spiro[acenaphthylene‐1(2H),4′‐[4H‐indeno[1,2‐b]pyridines] by the reaction of indane‐1,3‐dione, 1,3‐dicarbonyl compounds, isatins (=1H‐indole‐2,3‐diones) or acenaphthylene‐1,2‐dione, and AcONH₄ in refluxing toluene in the presence of a catalytic amount of pyridine is reported.     

Synthesis and Triethylamine‐catalyzed Cyclization Reaction of 4‐Pentyne‐1,3‐dione System Having Various Substituents

4-Pentyne-1,3-dione system having various substituents was synthesized in two steps and the cyclization behavior of the obtained 1,3-dicarbonyl compounds was examined. γ-Pyrones and 2-alkylidene-2,3-dihydro-3-furanones were obtained by the triethylamine-catalyzed cyclization of the 4-pentyne-1,3-dione system having a diketone moiety. Furthermore, a phenol derivative was obtained in the case of 4-pentyne-1,3-dione system having an ester moiety. Thus, it was found that the kind of substituents in the 4-pentyne-1,3-dione system remarkably influenced the selectivity in the cyclization.     

From Homoconjugated Push–Pull Chromophores to Donor–Acceptor‐Substituted Spiro Systems by Thermal Rearrangement

Series of homoconjugated push–pull chromophores and donor–acceptor (D–A)‐functionalized spiro compounds were synthesized, in which the electron‐donating strength of the anilino donor groups was systematically varied. The structural and optoelectronic properties of the compounds were investigated by X‐ray analysis, UV/Vis spectroscopy, electrochemistry, and computational analysis. The homoconjugated push–pull chromophores with a central bicyclo[4.2.0]octane scaffold were obtained in high yield by [2+2] cycloaddition of 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ) to N,N‐dialkylanilino‐ or N,N‐diarylanilino‐substituted activated alkynes. The spirocyclic compounds were formed by thermal rearrangement of the homoconjugated adducts. They also can be prepared in a one‐pot reaction starting from DDQ and anilino‐substituted alkynes. Spiro products with N,N‐diphenylanilino and N,N‐diisopropylanilino groups were isolated in high yields whereas compounds with pyrrolidino, didodecylamino, and dimethylamino substituents gave poor yields, with formation of insoluble side products. It was shown by in situ trapping experiments with TCNE that cycloreversion is possible during the thermal rearrangement, thereby liberating DDQ. In the low‐yielding transformations, DDQ oxidizes the anilino species present, presumably via an intermediate iminium ion pathway. Such a pathway is not available for the N,N‐diphenylanilino derivative and, in the case of the N,N‐diisopropylanilino derivative, would generate a strained iminium ion (A1,3 strain). The mechanism of the thermal rearrangement was investigated by EPR spectroscopy, which provides good evidence for a proposed biradical pathway starting with the homolytic cleavage of the most strained (CN)C?C(CN) bond between the fused four‐ and six‐membered rings in the homoconjugated adducts.     

Incorporating two different chromophores onto a silicon atom: the crystal structure and photophysical properties of 9‐{4‐[(9,9‐dimethyl‐9H‐fluoren‐2‐yl)dimethylsilyl]phenyl}‐9H‐carbazole

The crystal structure of the title bifunctional silicon‐bridged compound, C₃₅H₃₁NSi, (I), has been determined. The compound crystallizes in the centrosymmetric space group P2₁/c. In the crystal structure, the pairs of aryl rings in the two different chromophores, i.e. 9‐phenyl‐9H‐carbazole and 9,9‐dimethyl‐9H‐fluorene, are positioned orthogonally. In the crystal packing, no classical hydrogen bonding is observed. UV–Vis absorption and fluorescence emission spectra show that the central Si atom successfully breaks the electronic conjugation between the two different chromophores, and this was further analysed by density functional theory (DFT) calculations.     

A Novel Route to 1‐Substituted 3‐(Dialkylamino)‐9‐oxo‐9H‐indeno[2,1‐c]pyridine‐4‐carbonitriles

Heptalenecarbaldehydes 1 / 1′ as well as aromatic aldehydes react with 3‐(dicyanomethylidene)‐indan‐1‐one in boiling EtOH and in the presence of secondary amines to yield 3‐(dialkylamino)‐1,2‐dihydro‐9‐oxo‐9H‐indeno[2,1‐c]pyridine‐4‐carbonitriles (Schemes 2 and 4, and Fig. 1). The 1,2‐dihydro forms can be dehydrogenated easily with KMnO₄ in acetone at 0° (Scheme 3) or chloranil (=2,3,5,6‐tetrachlorocyclohexa‐2,5‐diene‐1,4‐dione) in a ‘one‐pot’ reaction in dioxane at ambient temperature (Table 1). The structures of the indeno[2,1‐c]pyridine‐4‐carbonitriles 5′ and 6a have been verified by X‐ray crystal‐structure analyses (Fig. 2 and 4). The inherent merocyanine system of the dihydro forms results in a broad absorption band in the range of 515–530 nm in their UV/VIS spectra (Table 2 and Fig. 3). The dehydrogenated compounds 5, 5′ , and 7a – 7f exhibit their longest‐wavelength absorption maximum at ca. 380 nm (Table 2). In contrast to 5 and 5′, 7a – 7f in solution exhibit a blue‐green fluorescence with emission bands at around 460 and 480 nm (Table 4 and Fig. 5).     

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.     

Redox‐Active Metal–Organic Frameworks: Highly Stable Charge‐Separated States through Strut/Guest‐to‐Strut Electron Transfer

Molecular organization of donor and acceptor chromophores in self‐assembled materials is of paramount interest in the field of photovoltaics or mimicry of natural light‐harvesting systems. With this in mind, a redox‐active porous interpenetrated metal–organic framework (MOF), {[Cd(bpdc)(bpNDI)] ? 4.5 H₂O ? DMF}_n ( 1 ) has been constructed from a mixed chromophoric system. The μ‐oxo‐bridged secondary building unit, {Cd₂(μ‐OCO)₂}, guides the parallel alignment of bpNDI (N,N′‐di(4‐pyridyl)‐1,4,5,8‐naphthalenediimide) acceptor linkers, which are tethered with bpdc (bpdcH₂=4,4′‐biphenyldicarboxylic acid) linkers of another entangled net in the framework, resulting in photochromic behaviour through inter‐net electron transfer. Encapsulation of electron‐donating aromatic molecules in the electron‐deficient channels of 1 leads to a perfect donor–acceptor co‐facial organization, resulting in long‐lived charge‐separated states of bpNDI. Furthermore, 1 and guest encapsulated species are characterised through electrochemical studies for understanding of their redox properties.     

Dipyrido[3,2‐a:2′,3′‐c]phenazine‐Based Donor–Acceptor Aromatic Heterocyclic Compounds with Thienyl and Triphenylamino Chromophores at the 2,7‐ and/or 10,13‐Positions

A series of T‐ and H‐shaped donor–acceptor (D–A) types of dipyrido[3,2‐a:2′,3′‐c]phenazine (DPPZ)‐based molecules, extended by thienyl and triphenylamino chromophores at the 2,7‐(bottom) and/or 10,13‐positions (top), have been designed and prepared successfully. Synthetic, structural, thermal, spectral, and computational comparisons have been carried out for related compounds because of their adjustable intramolecular charge‐transfer properties. It is noted that a pair of structural isomers ( 5 and 6 ) has been obtained, respectively, where distinguishable UV/Vis and fluorescence spectra, electrochemical activity, thermal stability, and bandgaps are observed. Furthermore, compounds 6 , 8 , 10 , 11 , 13 , and 15 exhibit excellent thermal stability, and the Td₁₀ values for them are found to range from 524 to 646 °C, which can be regarded as one of the best groups of thermally stable compounds among organic small molecules. In addition, theoretical calculations were performed, and the structure–property relationships were examined to reveal the effects of the position and number of donor arms on the DPPZ acceptor core.     

Is Our Way of Thinking about Excited States Correct? Time‐Resolved Dispersive IR Study on p‐Nitroaniline

Low‐lying excited electronic states of an important class of molecules known as push–pull chromophores are central to understanding their potential nonlinear optical properties. Here we report that a combination of high‐sensitivity nanosecond time‐resolved dispersive IR spectroscopy and DFT calculations on p‐nitroaniline (PNA), a prototypical push–pull molecule, reveals that PNA in the lowest excited triplet state has a partial quinoid structure. In this structure, the quinoid configuration is restricted to a part of the phenyl ring adjacent to the NO₂ group. The partial quinoid structure of PNA cannot be explained by a commonly used hybrid of a neutral form and a zwitterionic charge‐transfer form. Our findings not only cast doubt on the general applicability of the classical way of looking at excited states, based exclusively on characteristic resonance structures, but also provide deeper insights into excited‐state structure of highly polarizable molecular systems.