Hiroki Fukumoto

The First Observation of 1H-NMR Spectrum of Pentacene

Despite much interest in pentacene as a promising organic semiconductors, its chemical properties have scarcely been elucidated. Even such a fundamental data as 1H-NMR spectrum has not been reported yet due to poor solubility of pentacene in various solvents. Here we report the first observation of 1H NMR spectrum of pentacene by using dimethyl sulfoxide-d6 as solvent and heating the sample to 80°C. Not only the signal assignment but also the easily oxidizable property of pentacene was verified from the comparison between the spectra measured in degassed and non-degassed solvents.

Energy gap dependence of the S2→S1 internal conversion of α,ω-diphenylpolyenes (N=3–8) in solution phase

Abstract By using femtosecond and picosecond transient absorption measurement techniques, we have investigated the dynamic behavior of the S 2 state of all-trans - α , ω -diphenylpolyenes, from diphenylhexatriene ( N =3) to diphenylhexadecaoctaene ( N =8), in solution. The S 2 state lifetimes, which were determined from the decay of the S n ←S 2 absorption band around 700 nm, were similar for N =3–7. The observed small energy gap dependence of the S 2 →S 1 internal conversion rate can be an indication of the large difference in the molecular geometry of the S 1 and S 2 states.

Formation of lanthanoid(II) and lanthanoid(III) thiolate complexes derived from metals and organic disulfides: crystal structures of [{Ln(SAr)(µ-SAr)(thf)3}2](Ln = Sm, Eu), [Sm(SAr)3(py)2(thf)] and [Yb(SAr)3(py)3](Ar = 2,4,6-triisopropylphenyl; py = pyridine)

Reaction of metallic samarium, europium and ytterbium with bis(2,4,6-triisopropylphenyl) disulfide gave selectively LnII thiolate complexes, [{Ln(SAr)(µ-SAr)(thf)3}2] Ln = Sm 1; Ln = Eu 2 and [Yb(SAr)2(py)4]3, as well as LnIII thiolate complexes, [Ln(SAr)3(py)n(thf)3–n]: Ln = Sm, n= 3 4a; Ln = Sm, n= 2 4b; Ln = Yb, n= 3 5, (Ar = 2,4,6-trisopropylphenyl) depending on the stoichiometry of the lanthanoid and the disulfide; the molecular structures of 1, 2, 4b and 5 were determined by X-ray crystallography.

Preparation and Properties of Poly[(2‐alkylbenzimidazole)‐alt‐thiophene]s with Long Alkyl Side Chains

New alternative copolymers of thiophene and benzimidazole with alkyl side chains (alkyl = n-C 5 H 11 , n-C 7 H 15 , N-C 10 H 21 , n-C 12 H 25 , and n-C 18 H 37 ) have been prepared. The polymerization by Stille coupling of 2-alkyl-4,7-dibromobenzimidazoles with 2,5-bis(trimethylstannyl)thiophene gave the corresponding copolymers in good yields. The new copolymers showed absorption and photoluminescence peaks at about 436-460 and 520-530 nm, respectively. Quantum yields of the photoluminescence were about 21-37% in DMF. Addition of NaOH led to a red-shift of the absorption peak by about 60 nm. Their XRD patterns showed a diffraction peak in a low angle region (Bragg spacing d 1 = 17.4-35.4 A) and a broad peak at about d 2 = 4.0 A. Plots of the d 1 space vs. the number of carbon atom in the alkyl side chain gave a linear line with a slope of 1.35 A per carbon, suggesting an end-to-end type packing of the copolymer in the solid.

Ligand exchange reactions of a 1,3-butadiene complex of magnesium

Abstract The ligand exchange reaction of a diene ligand bound to magnesium was investigated. Reaction of the magnesium-butadiene compound [Mg(C 4 H 6 )(thf) 2 ] n ( 2 ) with 1,4-diphenyl-1,3-butadiene afforded Mg(s- cis -1,4-diphenyl-1,3-butadiene)(thf) 3 ( 1 ) together with butadiene. Similarly, treatment of 2 with 1,6-diphenyl-1,3,5-hexatriene, anthracene, and 1,3,5,7-cycIooctatetraene afforded the corresponding magnesium adducts Mg(1,6-diphenyl-1,3,5-hexatriene)(thf) 3 ( 3 ) Mg(anthracene)(thf) 3 ( 4 ), and Mg(cot)(thf) 2,5 ( 5 ), respectively, in addition to the liberated butadiene. Reaction of 2 with diphenylacetylene in THF also induced the ligand exchange reaction, resulting in the formation of a diphenylacetylene adduct [Mg(PhC 2 Ph)(thf)] 4 ( 6 ) of magnesium.

Preparation and Chemical Properties of π-Conjugated Polymers Containing Indigo Unit in the Main Chain

π-Conjugated polymers based on indigo unit were prepared. Dehalogenative polycondensation of N-hexyl-6,6′-dibromoindigo with a zerovalent nickel complex gave a homopolymer, P(HexI), in 77% yield. Copolymer of N-hexyl-indigo and pyridine, P(HexI-Py), was also prepared in 50% yield. P(HexI) showed good solubility in organic solvents, whereas P(HexI-Py) was only soluble in acids such as HCOOH. The weight-average molecular weights (Mw) of P(HexI) and P(HexI-Py) were determined to be 10,000 and 40,000, respectively, by a light scattering method. Pd-catalyzed polycondensation between 6,6′-dibromoindigo with N-BOC (BOC = t-butoxycarbonyl) substituents and a diboronic compound of 9,9-dioctylfluorene afforded the corresponding alternating copolymer, P(BOCI-Flu), as a deep red solid in 98% yield. P(BOCI-Flu) was soluble in N-methyl-2-pyrroridone and showed an Mw of 29,000 in GPC analysis. Treatment of P(BOCI-Flu) with CF3COOH smoothly led to a BOC-deprotection reaction to give an insoluble deep green polymer, P(I-Flu), in a quantitative yield. Diffuse reflectance spectra of powdery P(BOCI-Flu) and P(I-Flu) showed peaks at about 580 nm and 630 nm, respectively, which are thought to originate from the indigo unit.

Synthesis and Basic Optical Properties of New π-Conjugated Thiophene-Pyridine Co-oligomers

Two series of π-conjugated thiophene-pyridine co-oligomers, Py-Th-(Th) m -Th-Py (Py = pyridine unit; Th = thiophene unit; 4a: m = 0; 5a: m = 1; 6a: m = 2) and Th-Py-(Th) m -Py-Th (4b: m = 0; 5b: m = 1; 6b: m = 2), have been prepared by palladium- or nickel-promoted C-C coupling reaction in high yields. The π-π * absorption peak of Py-Th-(Th) m -Th-Py (390-440 nm) is observed at a longer wavelength than that of Th-Py-(Th) m -Py-Th (345-410 nm) with the same m number. These UV-vis data are considered to reflect a charge transfer (CT) interaction between the thiophene (donor) and pyridine (acceptor) units. 4a-6a, 5b, and 6b show photoluminescence in a range of 430-540 nm and give quantum yields (Φ) of 20-40%. 4b affords a high quantum yield of Φ= 71%. A linear correlation holds between the π-π* transition energy and the inverse of the number of the aromatic units [1/(m+4)] for the 4a-6a and 4b-6b series.

Cationic monocyclooctatetraenyl-lanthanoid complexes derived from metallic lanthanoid: crystal structures of [Sm(η8−C8H8)(hmpa)3]I and [Sm(η8−C8H8)(hmpa)3][Sm(η8−C8H8)2] (HMPA = hexamethylphosphoric triamide)

Abstract Addition of an excess hexamethylphosphoric triamide (abbr. HMPA) to a neutral complex SmI( ν 8 −C 8 H 8 (thf) ( 1 ) (C 8 H 8 = 1,3,5,7-cyclooctatetraene), which was prepared by a direct reaction of metallic samarium with C 8 H 8 in the presence of iodine in THF, afforded a cationic samarium complex [Sm( η 8 −C 8 H 8 )(hmpa) 3 ]I ( 2 ). Complex 2 can also be prepared by a simple one-pot reaction of stoichiometric amounts of metallic samarium, cyclooctatetraene, and iodine in the presence of an excess HMPA at 50°C. With a catalytic amount of iodine, ionic complexes of general formula Ln (η 8 − C 8 H 8 )( hmpa ) n ][ Ln (η 8 − C 8 H 8 ) 2 ] [ Ln = La and n = 4 ( 6 ); Ln = Sm and n = 3 ( 7 ) ] were obtained by treating metallic lanthanum or samarium, respectively with cyclooctatetraene in the presence of HMPA. The structure of the diamagnetic complex 6 as well as the paramagnetic complexes 2 and 7 was determined by 1 H NMR spectroscopy. Crystal structures of 2 and 7 were revealed by X-ray analyses, indicating that these complexes comprised of a cationic [Sm( η 8 −C 8 H 8 )(hmpa) 3 ] + and an anionic part; for 2 and 7 being I − and [Sm( η 8 −C 8 H 8 ) 2 ] − , respectively.

DIBROMIDES OF BOC-PROTECTED 1-AMINOPYRROLE AND 4-AMINO-1,2,4-TRIAZOLE : SYNTHESIS, X-RAY MOLECULAR STRUCTURE, AND NMR BEHAVIOR

α-Dibromides of BOC-protected 1-aminopyrrole and 4-amino-l,2,4-triazole have been prepared and their molecular structures have been confirmed by X-ray crystallography. They can be used for polymer synthesis.

Polymerization of acrylonitrile catalyzed by thiolate complexes of divalent and trivalent lanthanoids

Arenethiolate complexes of lanthanoid(II) and lanthanoid(III) metals were used as initiators for the polymerization of acrylonitrile at - 78°C in THF, giving atactic and high molecular mass (M n 10 5 ) polyacrylonitriles in good yield.