N-2,6-Di(isopropyl)phenyl-2-azaphenalenyl radical cations.

N-2,6-Di(isopropyl)phenyl-2-azaphenalenyl radical cations were obtained as a dark brown air-sensitive crystalline compound. The high HOMA values and the ACID calculation indicate relatively high aromatic character of a 5,8-di-tert-butyl derivative, and clean generation of a derivative without tert-butyl groups indicates that the di(isopropyl)phenyl group is sufficient for hampering the formation of the σ-dimer.

9,9-Bis[4-(N-aryl)phenyl]methylidene-xanthylidene Derivatives Displaying Mechano-, Crystallo-, and Thermochromism.

Tetraphenylethylene (TPE) derivatives bearing a xanthene moiety are of interest because they have novel optical properties. 9,9-Bis[4-(N,N-diphenylamino)phenyl] and 9,9-bis[4-(9-carbazolyl)-phenyl]methylidene-xanthylidenes 3 and 4 were synthesized using Suzuki-Miyaura coupling of 9,9-dibromomethylidene-xanthylidene with the corresponding boronic acids. Diphenylamino derivative 3 exhibits mechanochromism and mechanofluorochromism (MC and MFC) reflected in absorption and fluorescence color changes. In contrast, carbazolyl derivative 4 displays thermo- and crystallo-chromism in addition to MC and MFC in the solid state. Powder X-ray diffraction and single crystal X-ray crystallographic analysis reveal that the solid state photophysical properties of these substances are governed by conformational changes rather by the creation of planar π-conjugation extended geometries.

Highly Polarized Benzo[k]fluoranthene Imide Derivatives: Large Solvatofluorochromism, Dual Fluorescence and Aggregation Induced Emission Associated with Excited-State Intramolecular Charge Transfer.

The highly conjugated imides, 9-diphenyl-aminobenzo[k]fluoranthene imide and N-phenylcarbazo[2,3-k]fluoranthene imide, were produced by Buchwald-Hartwig reaction of N-octyl-9,10-dibromobenzo[k]fluoranthene imide with diphenylamine. In a similar manner, reaction of the N-ethylhexyl-9,10-dibromo derivative with carbazole leads to formation of 9-(N-carbazoyl)benzo[k]fluoranthene imide. All the benzo[k]fluoranthene imide (BFI) derivatives in solution show remarkable solvatofluorochromism. Diphenylamino and 9-(N-carbazoyl) derivatives, having twisted structures, exhibit fluorescence bands at short wavelengths in highly polar solvents, and they emit dual fluorescence in acetone. Moreover, the 9-(N-carbazoyl) derivative displays aggregation-induced emission in highly aqueous acetone solutions. The results of density functional theory calculations demonstrate that a considerable spatial separation exists between the HOMO and LUMO coefficients of the N-arylamine substituted BFIs. The results indicate that the ground-to-excited state transitions of these compounds have intramolecular charge transfer character.

Synthesis and Properties of a Decacyclene Monoimide and a Naphthalimide Derivative as Three-Dimensional Acceptor-Donor-Acceptor Systems.

A method involving the Diels-Alder (DA) cycloaddition of diacenaphtheno[1,2-b;1',2'-d]thiophenes (DATs) with N-alkylacenaphthylene-5,6-dicarboximides (AIs) was developed to synthesize decacyclene monoimides (DCMIs). The reactions generate the corresponding 1:2 adducts (BAIAs) as major products together with 1:1 adducts (the DCMIs). The molecular structure of BAIAb (N-octyl derivative) was unambiguously assigned as the bis-adduct having an endo,endo spatial disposition of the two acenaphthylene-5,6-dicarboximide moieties by using X-ray crystallographic analysis. Relative to the absorption spectrum of decacyclene triimide (DCTIa, N-2-ethylhexyl derivative), that of the analogous N-2-ethylhexyl-substituted monoadduct, DCMIa, is bathochromically shifted despite the fact that it possesses a less delocalized π-electron system. DCMIa does not fluoresce in various organic solvents, whereas DCTIa emits yellow fluorescence in CH2 Cl2 with a low quantum yield (ΦSN ). Moreover, DCMIa in CDCl3 displays concentration-dependent 1 H NMR spectroscopy behavior, which suggests that it self-aggregates with an association constant (Ka ) of (193±50) m-1 at 20 °C. Despite the presence of four bulky tert-butyl groups in DCMIa, its Ka value for aggregate formation is comparable to that of DCTIa [(495±42) m-1 ], which does not contain tert-butyl substituents. Spectroscopic studies with the bis-adduct BAIAa (N-2-ethylhexyl derivative) show that it displays remarkable solvatofluorochromism corresponding to an emission maximum shift (ΔλEM ) of 100 nm. The results of density functional theory calculations on BAIAc (N-methyl derivative) demonstrate that a considerable spatial separation exists between the HOMO and LUMO coefficient distributions, which indicates that the ground-to-excited state transition of the novel three-dimensional acceptor-donor-acceptor BAIAa system should have intramolecular charge-transfer character.

Bicyclo[6.3.0]undeca-1(11),2,4,6,8-pentaen-10-ylidene: An Aromatic Carbene with Ambiphilic Properties.

The title carbene (4) was generated as a highly reactive species in solution by photoirradiation of 10-diazobicyclo[6.3.0]undecapentaene (5) using a high-pressure mercury lamp. Carbene 4 reacts with benzene to afford two isomeric adducts, 10-phenylbicyclo[6.3.0]undecapentaene (10) and tricyclo[9.3.03, 10 .0]heptadeca-1,3(10),4,6,8,12,14,16-octaene (11). The reactivity toward benzene is a characteristic of an electrophilic aromatic carbene analogous to cyclopentadienylidene 1. In contrast, the reaction of 4 with methanol produces 7-methoxybicyclo[6.3.0]undeca-1,3,5,8,10-pentaene (15). When [D1 ]methanol was employed as a reactant, the 10-deuterated analogue was formed. The results clearly indicate the formation of bicyclo[6.3.0]undecapentaenyl cation (7) as a novel 10 π-electronic compound by protonation of 4. Theoretical calculations indicate that the 2- and 7-positions of the cation have the largest positive charge in the cation. Moreover, the carbene was generated in the presence of tert-butyl hydroperoxide in aqueous tetrahydrofuran to afford azulene through oxidation of 7, followed by decarbonylation. The nucleophilic property of carbene 3 is similar to that of cycloheptatrienylidene 2. Thus, 4 can be regarded as a novel ambiphilic aromatic carbene.

Phthalimide Compounds Containing a Trifluoromethylphenyl Group and Electron-Donating Aryl Groups: Color-Tuning and Enhancement of Triboluminescence.

Trifluoromethylphenyl-substituted phthalimide derivatives favorably form triboluminescence (TL) active noncentrosymmetric crystals. Oligothienyl-, oligophenyl-, and naphthyl-substituted phthalimide derivatives were successfully developed as a series of metal free TL compounds. X-ray crystal structure analyses of bithienyl and naphthyl derivatives revealed noncentrosymmetric layer structures in the same direction. Introduction of suitable electron rich π-units such as thienyl groups enhances their photoluminescence and TL characteristics, and the colors can be also controlled in the visible region. A rigid naphthyl-substituted imide derivative exhibits extremely high TL performance.

π-Extended Pentalenes: The Revival of the Old Compound from New Standpoints.

Polycyclic conjugated systems bearing carbocyclic five-membered rings have attracted much attention due to their novel electronic properties and utility in organic electronic devices. Despite possessing a 4nπ electron periphery, dibenzopentalenes have a planar structure and are fairly stable. Thus, appropriate modifications should provide desirable electronic properties. Recently, we have discovered novel Ni-catalyzed coupling reactions that constitute a versatile new route to dibenzopentalene derivatives from readily available o-bromoethynylbenzenes. Moreover, we developed another dibenzopentalene synthesis using indenone derivatives as important intermediates. These methods are applicable to π-extended pentalene derivatives possessing various functional groups and aromatic ring systems. Among them, a dinaphthylpentalene derivative shows a high hole mobility (1.8 × 10(-3) cm(2) V(-1) s(-1) ) for an amorphous material. Furthermore, this is the first pentalene derivative that can be employed as a p-type material for organic heterojunction photovoltaic cells (PCE = 0.94%, V(OC) = 0.96 V) and as organic thin-film semiconductors.

Direct arylations for study of the air-stable P-heterocyclic biradical: from wide electronic tuning to characterization of the localized radicalic electrons.

We have developed methods for installing aryl substituents directly on the phosphino groups of the 1,3-diphosphacyclobutane-2,4-diyl system. The aryl substituents tuned the electronic and structural characteristics of the biradical unit both in solution and in the solid state. 1-tert-butyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobuten-4-yl anion, prepared from phosphaalkyne (Mes*C≡P; Mes* = 2,4,6-tBu3C6H2) and t-butyllithium, was allowed to react with an electron-deficient N-heterocyclic reagent. The corresponding N-heteroaryl-substituted P-heterocyclic biradicals were produced via SNAr reactions. Biradicals bearing perfluorinated pyridyl substituents exhibited photoabsorption properties comparable to those of previously reported derivatives because the highest occupied and lowest unoccupied molecular orbit levels were reduced by a similar amount. In contrast, the triazine substituent reduced the band gap of the biradical unit, and the large red shift in the visible absorption and high oxidation potential were further tuned via subsequent SNAr and Negishi coupling reactions. The amino-substituted triazine structure provided a strongly electron-donating biradical chromophore, which produced unique p-type semiconducting behavior even though there was no obvious π-overlap in the crystalline state. The single-electron transfer reaction involving Mes*C≡P, phenyllithium, and iodine afforded 1,3-diphenyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl via the intermediate P-heterocyclic monoradical. The tetraaryl-substituted symmetric biradical product was used to determine the electron density distribution from the X-ray diffraction data. The data show highly localized radicalic electrons around the skeletal carbon atoms, moderately polarized skeletal P-C bonds in the four-membered ring, and no covalent transannular interaction.

Solution-processed and air-stable n-type organic thin-film transistors based on thiophene-fused dicyanoquinonediimine (DCNQI) deriatives.

π-Conjugated systems 2a and 2b containing thiophene-fused DCNQI with long alkyl and trifluoromethylphenyl groups were synthesized as potential active materials for solution-processed and air-stable n-type organic thin-film transistors (OTFTs). The electrochemical measurements revealed that the lowest unoccupied molecular orbital (LUMO) of the compounds have an energy level less than -4.0 eV, indicating air stable n-type materials. The long alkyl groups endowed the compounds good solubility and solution-processability. X-ray diffraction measurements revealed the difference of the molecular arrangement depending on the alkyl groups, which were also observed in the UV-vis absorptions of the films. A relatively good mobility up to 0.003 cm(2) V(-1) s(-1) for 2a by spin-coating was obtained with good air stability.

Synthesis, crystal structures, and properties of 6,12-diaryl-substituted indeno[1,2-b]fluorenes.

Fused polycyclic indeno[1,2-b]fluorene derivatives with aryl substituents at the 6,12-positions have been prepared as a potential antiaromatic 20π electronic system. They showed strong absorptions in the visible region and amphoteric redox properties. The quinoid-type molecular structures were revealed by X-ray crystal-structure analysis, which indicated that the bond lengths of the quinoid unit depend on the aryl substituents. Whereas nucleus-independent chemical shift NICS(1) calculations indicate the antiaromatic nature of the s-indacene core, they have higher stability than substituted acene derivatives. The derivatives with difluorophenyl or anthryl groups were stable in solution. Vapor-deposited thin films showed ambipolar carrier transportation in the field-effect transistor devices.

Ambipolar behavior of hydrogen-bonded diketopyrrolopyrrole-thiophene co-oligomers formed from their soluble precursors.

Organic field-effect transistors with hydrogen-bonded diketopyrrolopyrrole-thiophene co-oligomers were fabricated by a solution-process method with annealing at 200 °C, showing ambipolar charge-carrier transfer with field-effect mobilities up to µ(h) = 6.7 × 10(-3) cm(2) V(-1)s(-1) and µ(e) = 5.6 × 10(-3) cm(2) V(-1) s(-1).

Hysteretic Tricolor Electrochromic Systems Based on the Dynamic Redox Properties of Unsymmetrically Substituted Dihydrophenanthrenes and Biphenyl-2,2'-Diyl Dications: Efficient Precursor Synthesis by a Flow Microreactor Method.

A series of biphenyl-2,2'-diylbis(diarylmethanol)s 3, which have two kinds of aryl groups at the bay region, were efficiently obtained by integrated flow microreactor synthesis. The diols 3NO/NX are the precursors of unsymmetric biphenylic dications 2NO/NX2+, which are transformed into the corresponding dihydrophenanthrenes 1NO/NX via 2NO/NX+• upon reduction, when they exhibit two-stage color changes. On the other hand, the steady-state concentration of the intermediate 2NO/NX+• is negligible during the oxidation of 1NO/NX to 2NO/NX2+, which reflects unique tricolor electrochromicity with a hysteretic pattern of color change [color 1→color 2→color 3→color 1].

Synthesis and properties of terthiophene and bithiophene derivatives functionalized by BF2 chelation: a new type of electron acceptor based on quadrupolar structures.

Terthiophene and bithiophene derivatives functionalized by BF(2) chelation were synthesized as a new type of electron acceptor, and their properties were compared to those of bifuran and biphenyl derivatives. These new compounds are characterized by quadrupolar structures due to resonance contributors generated by BF(2) chelation. The bithiophene derivative has a strong quadrupolar character compared with the bifuran and biphenyl derivatives because their hydrolytic analyses indicated that the bithiophene moiety has a larger on-site Coulomb repulsion than the others. The terthiophene derivative has a smaller on-site Coulomb repulsion than the bithiophene derivative due to the addition of a thiophene spacer. These BF(2) complexes exhibit long-wavelength absorptions and according to measurements of ionization potentials and absorption edges they have energetically low-lying HOMOs and LUMOs. The crystal structure of the bithiophene derivative is of the herringbone type, with short F···S and F···C contacts affording dense crystal packing. n-Type semiconducting behaviour was observed in organic field-effect transistors based on these BF(2) complexes.

Dithienylbenzobis(thiadiazole) based organic semiconductors with low LUMO levels and narrow energy gaps.

Novel OFET materials showing high mobility (0.77 cm2 V(-1) s(-1)) and good air-stability were developed using a benzobis(thiadiazole) (BBT) unit and the high FET performance was attributed to the low LUMO level and the film morphology.

Novel semiconducting quinone for air-stable n-type organic field-effect transistors.

Quinones are promising moieties for n-type organic semiconductors due to their high electron affinity. Benzo[1,2-b:4,5-b']dithiophene-4,8-dione derivative with a quinone moiety have been synthesized, characterized, and used as active layer of organic field-effect transistors (OFETs). This derivative has deep LUMO level, leading to efficient charge-carrier injection and air stability. In addition, it forms a columnar structure with efficient intermolecular pi-pi and horizontal direction interactions, leading to high electron mobilities. In fact, OFET devices fabricated here showed good n-type characteristics, where the electron mobility was 0.15 cm(2) V(-1) s(-1) under vacuum conditions and above 0.1 cm(2) V(-1) s(-1) in air.

Synthesis, crystal structure, and electron-accepting property of the BF2 complex of a dihydroxydione with a perfluorotetracene skeleton.

A BF(2) complex containing an octafluorotetracene moiety was synthesized as a new type of electron acceptor. This compound exhibits a long-wavelength absorption based on the perfluorotetracene skeleton and high electron affinity due to its quadrupolar structure enhanced by fluorination. In the crystal, the molecules are arranged with short F...pi and F...F contacts affording a dense crystal packing. The BF(2) complex exhibited n-type semiconducting behavior.

Anthraquinone derivatives affording n-type organic thin film transistors.

New anthraquinone derivatives were prepared and used as active layers of organic field-effect transistors (OFETs); these devices showed good n-type characteristics and the quinones were found to be useful for organic semiconductors in OFETs.

Synthesis, crystal structure, and physical properties of 7,14-disubstituted pentacene-5,12-diones containing a methylenequinoid structure.

Title 7,14-disubsituted pentacene-5,12-diones were prepared for the first time by a nucleophilic substitution reaction of a pentacene-5,7,12,14-tetraone with aryl- or ethynyllithiums followed by a dehydroxylation reaction. The methylenequinoid structures with two conjugated carbonyl groups were clearly observed in their crystal structures. They showed intense absorptions in the visible region and amphoteric redox properties with high reduction potentials.

Synthesis and properties of BF2 complexes to dihydroxydiones of tetracene and perylene: novel electron acceptors showing n-type semiconducting behavior.

BF(2) complexes containing tetracene and perylene moieties were synthesized as new types of electron-deficient arene compounds. These compounds exhibit long wavelength absorption and high electron affinities, as revealed through spectral and electrochemical studies, due to their quadrupolar structures represented by resonance contributors. The BF(2) complex containing tetracene exhibits an n-type semiconducting behavior. These compounds are new types of electron acceptors functionalized by BF(2) chelation.

Phosphorescent iridium complexes based on 2-phenylimidazo[1,2-a]pyridine ligands: tuning of emission color toward the blue region and application to polymer light-emitting devices.

A series of new blue-phosphorescent iridium(III) complexes 1-14 with ligands of 2-phenylimidazo[1,2-a]pyridine (pip) derivatives were successfully prepared, and their electrochemical, photophysical, and electroluminescent (EL) properties were systematically investigated. It was found that the emission maxima are significantly dependent on the substituents on the phenyl ring in the range of 489-550 nm. For instance, electron-withdrawing groups such as F and CF3 shift the emission maxima to shorter wavelengths by lowering the HOMO levels (complexes 4-8), whereas the extended pi-conjugation leads to bathochromic shifts (2, 3). To obtain further information about the frontier orbital, substitution effects on the imidazole part were also investigated here, and it was found that electron-withdrawing or -donating substituents on the imidazole ring affected the emission maxima (9, 557 nm; 10, 525 nm). These results including their oxidation potentials suggest that the HOMO of the pip-based complex is a mixture of Ir-d, phenyl-pi, and imidazole-pi orbitals. From this viewpoint, combination of electron-withdrawing substituents on the phenyl ring with the use of another ancillary ligand enabled further blue shifts (13, 468, 499 nm; 14, 464, 494 nm). This new system based on pip is one of the rare examples of iridium complexes whose emissions can be tuned to the blue region. Preliminary polymer light-emitting devices (PLEDs) employing the Ir complexes were fabricated, and the devices showed moderate EL efficiencies.