Hidetaka Nishimura

Hole-Transporting Materials with a Two-Dimensionally Expanded π-System around an Azulene Core for Efficient Perovskite Solar Cells

Two-dimensionally expanded π-systems, consisting of partially oxygen-bridged triarylamine skeletons that are connected to an azulene (1-3) or biphenyl core (4), were synthesized and characterized. When tetra-substituted azulene 1 was used as a hole-transporting material (HTM) in perovskite solar cells, the observed performance (power conversion efficiency = 16.5%) was found to be superior to that of the current HTM standard Spiro-OMeTAD. A comparison of the hole mobility, the ability to control the HOMO and LUMO levels, and the hole-collection efficiency at the perovskite/HTM interface in 1 with reference compounds (2-4 and Spiro-OMeTAD) led to the elucidation of key factors required for HTMs to act efficiently in perovskite solar cells.

Dynamic Optical Properties of CH3NH3PbI3 Single Crystals As Revealed by One- and Two-Photon Excited Photoluminescence Measurements

The dynamic optical properties of perovskite CH3NH3PbI3 single crystals were studied by means of time-resolved photoluminescence (PL) spectroscopy at room temperature. The PL peak under one-photon excitation exhibits a red-shift with elapsing time, while two-photon PL is time-independent and appears at lower energy levels. The low-energy two-photon PL can be attributed to emissions from the localized states because of strong band-to-band absorption and photon re-absorption of the emitted light in the interior region. We revealed that the PL behaviors can be explained by the diffusion of photocarriers generated in the near-surface region to the interior region. The excitation fluence dependence of the one-photon PL dynamics is also discussed in terms of the electron-hole radiative recombination and carrier diffusion effects.

On‐Top π‐Stacking of Quasiplanar Molecules in Hole‐Transporting Materials: Inducing Anisotropic Carrier Mobility in Amorphous Films

Dimers of partially oxygen-bridged triarylamines were designed and synthesized as hole-transporting materials. X-ray structural analyses revealed that these compounds form on-top π-stacking aggregates in the crystalline state. TRMC measurements showed that high levels of anisotropic charge transport were induced in the direction of the π-stacking. Surprisingly, even in vacuum-deposited amorphous films, these compounds retained some of the face-on π-stacking, thus facilitating an out-of-plane carrier mobility.

Excimer emission based on the control of molecular structure and intermolecular interactions

Three triple-core chromophore derivatives based on anthracene and pyrene or chrysene moieties, 1,6-bis-(10-[1,1′;3′,1′′]terphenyl-5′-yl-anthracen-9-yl)-pyrene (1,6 DAP-TP), 6,12-bis-(10-[1,1′;3′,1′′]terphenyl-5′-yl-anthracen-9-yl)-chrysene (DAC-TP), and 2,7-bis-(10-[1,1′;3′,1′′]terphenyl-5′-yl-anthracen-9-yl)-pyrene (2,7 DAP-TP), were designed and synthesized. For 1,6 DAP-TP, anthracene was attached to the 1,6 positions of pyrene. In the case of DAC-TP, two anthracenes were connected to chrysene, located at the center position within the core, whereas in 2,7 DAP-TP anthracene was connected to the 2,7 positions of pyrene. All three materials had highly twisted core structures and bulky m-terphenyl side groups introduced into the core. Excimer emission was observed in the solid film state and can be interpreted as the result of anisotropic intermolecular alignment (orientation effect). The wavelength of excimer formation was controlled through the change of the center position of the triple-core chromophore, and the color coordinate of white light and efficiency could be controlled when the materials were used in an electroluminescence (EL) device. Excimer EL emissions of 1,6 DAP-TP, DAC-TP, and 2,7 DAP-TP were at 591 nm, 556 nm, and 538 nm, respectively, and CIE coordinate values of the devices were (0.37, 0.31), (0.30, 0.37), and (0.32, 0.44), respectively, showing single molecular white emission. 2,7 DAP-TP showed a white OLED efficiency of 6.01 cd A−1 at 10 mA cm−2.

Oxygen-Bridged Diphenylnaphthylamine as a Scaffold for Full-Color Circularly Polarized Luminescent Materials

An oxygen-bridged diphenylnaphthylamine with a helical shape was designed and synthesized as a key scaffold for circularly polarized luminescent (CPL) materials. The introduction of electron-withdrawing groups, such as formyl and 2,2-dicyanovinyl substituents at the naphthyl moiety in this skeleton effectively decreases the LUMO level and thus allows a tuning of the band gap. The prepared model compounds exhibit intense CPL signals with a dissymmetry factor (g value) of 10-3 both in CH2Cl2 solutions and in the solid states. The emission colors of these derivatives are influenced both by the substituents as well as by solvent effects, covering the whole visible region from blue to deep red.

Mechanochemically-generated solid state complex of C60-fullerene with tetra-(5,7-diphenyl)calix[4]azulene, NMR, XRD and DFT studies

Abstract The synthesis of tetra-(5,7-diphenyl)calix[4]azulene via the reaction of 5,7-diphenylazulene with formaldehyde is described. Its solid-state supramolecular complexation with C60 produced by a grinding of the two components was evaluated by solid-state 13C-NMR spectroscopy and X-ray powder diffraction. Gas-phase DFT studies of possible structures are reported.

Calixazulenes: azulene-based calixarene analogues – an overview and recent supramolecular complexation studies

Some of the least studied calixarenes are those that consist of azulene rings bridged by -CH2- groups. Since Lash and Colby’s discovery of a simple and convenient method for producing the parent all-hydrocarbon calix[4]azulene, there have been two other all-hydrocarbon calix[4]azulenes which have been synthesized in good yields by their method. This allowed studying their supramolecular properties. This report is of our latest work on the solution-state supramolecular complexation of one of these calix[4]azulenes, namely tetrakis(5,7-diphenyl)calix[4]azulene or “OPC4A”, with several electron-deficient tetraalkyammonium salts. As a result of more recent methods developed by us and others employing Suzuki–Miyaura cross-coupling reactions to produce additional functionalized azulenes, the promise of further greater functionalized calixazulenes lies in store to be investigated.

White emission based on excimer emission control of triple core chromophores

Three materials had highly twisted molecular structures. In film state, excimer emission can be interpreted as result of orientation effect. Wavelength of excimer was controlled through the change of center position of triple core chromophore, and the CIE of white light could be controlled.