Masahiko Shibahara

Delocalization of Positive Charge in π-Stacked Multi-benzene Rings in Multilayered Cyclophanes

In the present study, delocalization of a positive charge in π-stacked multi-benzene rings in multilayered para- and meta-cyclophanes, in which benzene rings are connected by propyl chains to form a chromophore array with the face-to-face structure, was investigated by means of transient absorption spectroscopy during the pulse radiolysis using dichloroethane as a solvent. The local excitation and charge resonance (CR) bands were successfully observed. It was revealed that the CR band shifted to the longer wavelength side with the number of the benzene rings. The stabilization energy estimated from the peak position of the CR band showed the efficient charge delocalization over the cyclophanes. Furthermore, the CR bands showed the slight spectral change attributable to the change in distribution of the conformers. The substantially long lifetime of the CR band can be explained on the basis of the smaller charge distribution on the outer layers of the multilayered cyclophanes.

Synthesis, structure, and electronic and photophysical properties of two- and three-layered [3.3]Paracyclophane-based donor-acceptor systems (1)

The synthesis, structural, redox, and photophysical properties of the two- and three-layered donor-acceptor (D-A) type [3.3]paracyclophanes ([3.3]PCPs) are described. The synthesis of the two- and three-layered [3.3]PCPs 1 and 2 containing 2,1,3-benzothiadiazole (BTD) as an acceptor was achieved by the (p-ethylbenzenesulfonyl)methyl isocyanide coupling method. The cyclic voltammograms of 1 and 2 along with those of respective dione precursors 5 and 7 clearly indicate that the presence of the -CH(2)COCH(2)- bridge interferes with the electronic interactions between the BTD and the benzene rings, suggesting the importance of the through-bond interaction in the ground state. In sharp contrast, the UV/vis spectra of 1 and 5 as well as those of 2 and 7 exhibit similar bands regardless of the presence of the -CH(2)COCH(2)- or -CH(2)CH(2)CH(2)- bridges, indicating that the charge-transfer (CT) interaction is mainly responsible for the through-space interaction. The two-layered PCPs, 5 and 1, show broad structureless fluorescence bands at the same position of 468 nm, while those of the three-layered PCPs, 7 and 2, appear at 501 and 496 nm, respectively, with lower quantum yields compared to those of the two-layered PCPs probably due to the stronger intramolecular CT interaction of the three-layered PCPs in the ground state.

Optical Resolution, Absolute Configuration, and Chiroptical Properties of Three-Layered [3.3]Paracyclophane

A racemic mixture of three-layered [3.3]paracyclophane ([3.3]PCP), 1, has been resolved into two enantiomers, and their absolute configuration was determined from a comparison of experimental chiroptical properties and density functional theory (DFT) calculations. A simple model comprising two p-xylenes and 1,2,4,5-tetramethylbenzene (durene) was used to explain the origin of the chiroptical properties of the three-layered cyclophane system.

Four-layered [3.3]meta­cyclo­phane with ethene­tetra­carbo­nitrile

The title complex C42H48·2C6N4 {systematic name: heptacyclo[21.13.1.15,19.16,18.110,14.124,36.128,32]dotetraconta-1(37),5(40),6(41),10(42),11,13,18,23,28,30,32(39),36(38)-dodecaene–ethenetetracarbonitrile (1/2)}, consisting of four-layered [3.3]metacyclophane (MCP) with two tetracyanoethylene (TCNE) molecules, was grown from a mixture of MCP and TCNE in chloroform solution. The four-layered [3.3]MCP has an S-shaped structure in which three [3.3]MCP moieties take syn-(chair-boat), anti-(chair-boat) and syn-(chair-boat) conformations. The two outer [3.3]MCP moieties with syn geometry contain benzene rings with a tilt of 32.95 (7)°. The central [3.3]MCP moiety has an anti geometry, in which the two benzene rings are oriented parallel to each other at a transannular distance of 2.31 Å. The TCNE molecules are stacked on either side of the outer [3.3]MCP units at a distance of 3.19 Å on one side and 3.24 Å on the other, and showed 0.80:0.20 and 0.44:0.56 disorder, respectively.

Synthesis and physical properties of brominated hexacene and hole-transfer properties of thin-film transistors

A halide-substituted higher acene, 2-bromohexacene, and its precursor with a carbonyl bridge moiety were synthesized. The precursor was synthesized through 7 steps in a total yield of 2.5%. The structure of precursor and thermally converted 2-bromohexacene were characterized by solid state NMR, IR, and absorption spectra, as well as by DFT computation analysis. It exhibited high stability in the solid state over 3 months, therefore can be utilized in the fabrication of opto-electronic devices. The organic thin-film transistors (OFETs) were fabricated by using 2-bromohexacene and parent hexacene through vaccum deposition method. The best film mobility of 2-bromohexacene was observed at 0.83 cm2 V−1 s−1 with an on/off ratio of 5.0 × 104 and a threshold of −52 V, while the best film mobility of hexacene was observed at 0.076 cm2 V−1 s−1 with an on/off ratio of 2.4 × 102 and a threshold of −21 V. AFM measurement of 2-bromohexacene showed smooth film formation. The averaged mobility of 2-bromohexacene is 8 fold higher than the non-substituted hexacene.

Crystal structure of a four-layered [3.3](3,5)pyridino-phane.

The title compound {systematic name: 12,30-diazaheptacyclo[21.13.1.15,19.16,18.110,14.124,36.128,32]dotetraconta-1(37),5(40),6(41),10 (42),11,13,18,23,28,30,32 (39),36 (38)-dodecaene} has syn–anti–syn geometry. Two types of intermolecular short contacts are observed in its crystal structure.