The two-dimensional supramolecular structures of a series of N,N'-bis(n-alkyl)naphthalenediimides (NDIs), whose chain lengths span from C3 to C18, at a liquid-HOPG surface interface, studied by STM and FM-AFM, are assigned with the help of molecular dynamics/molecular mechanics calculations to demonstrate that the C3- and C4-NDIs show lamellar structures, the C4- to C12-NDIs show honeycomb (KAGOME) structures, and the C14- to C18-NDIs show lamellar structures again. The change in supramolecular structure depending on chain length can be explained semiquantitatively by the balance of entropy and enthalpy terms to show the importance of "self-avoiding walk" of the alkyl chain in entropy terms.

The design and development of organic phosphors that exhibit efficient emission at room temperature but do not contain precious metals such as iridium and platinum have attracted increasing attention. We report herein highly efficient green phosphorescence-emitting 1,4-dibenzoyl-2,5-bis(siloxy)benzene crystals in air at room temperature. Remarkable luminescence quantum yields of 0.46 to 0.64 and long lifetimes ranging from 76.0 to 98.3 ms were observed. Xray diffraction analysis of the single crystals revealed that there were several intermolecular interactions causing suppression of intramolecular motion, thereby minimizing nonradiative decay of the triplet excited state. Comparison with the corresponding 2,5-bis(dimethylphenylsilylmethyl) and 2,5-bis(trimethylsilyl) derivatives revealed that the siloxy groups are essential for efficient room temperature phosphorescence. Density functional calculations suggested that σ−n conjugation was operative in the siloxy moieties. Electron spin resonance measurement indicated that the radiative process included generation of the triplet diradical species, whose electron distribution was very similar to that of naphthalene. The present study largely expands the possibilities for the molecular design of precious metal-and halogen-free organic phosphors exhibiting efficient room temperature phosphorescence.

Rotational correlation time (τc) of nitroxide radical solute was determined in ionic liquids by utilizing CW EPR spectroscopy. The experimental values of τc determined in viscous ionic liquids disagree with the values calculated according to Stokes–Einstein–Debye (SED) equation. A fractional SED law was examined for these solute–solvent combinations.

Photodissociation of three oxime ester compounds was investigated using time-resolved electron paramagnetic resonance spectroscopy. Direct evidences for the appearance of methyl and iminyl radicals were obtained, and their reactivity toward the acrylate monomer was studied.

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Rotational motion of a nitroxide radical, peroxylamine disulfonate (PADS), dissolved in room temperature ionic liquids (RTILs) was studied by analyzing electron paramagnetic resonance spectra of PADS in various RTILs. We determined physical properties of PADS such as the hyperfine coupling constant (A), the temperature dependence of anisotropic rotational correlation times (τ(∥) and τ(⊥)), and rotational anisotropy (N). We observed that the A values remain unchanged for various RTILs, which indicates negligible interaction between the N-O PADS group and the cation of RTIL. Large N values suggest strong interaction of the negative sulfonyl parts of PADS with the cations of RTILs. Most of the τ(∥), τ(⊥), and (τ(∥)τ(⊥))(1/2) values are within the range calculated on the basis of a hydrodynamic theory with stick and slip boundary conditions. It was deduced that this theory could not adequately explain the measured results in some RTILs with smaller BF(4) and PF(6) anions.

We have investigated the emission properties of N,N'-diheptyl-3,4,9,10-perylenetetracarboxylic diimide thin films by the tunneling-electron-induced light emission technique. A fluorescence peak with vibronic progressions with large Stokes shifts was observed on both highly ordered pyrolytic graphite (HOPG) and Au substrates, indicating that the emission was derived from the isolated-molecule-like film condition with sufficient π-π interaction of the perylene rings of perylenetetracarboxylic diimide molecules. The upconversion emission mechanism of the tunneling-electron-induced emission was discussed in terms of inelastic tunneling including multiexcitation processes. The wavelength-selective enhanced emission due to a localized tip-induced surface plasmon on the Au substrate was also obtained.

In vivo quantification of extracellular pH (pHe) in tumour may provide a useful biomarker for tumour cell metabolism. In this study, we assess the viability of continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy with a pH-sensitive nitroxide to measure extracellular tumour pH in the mouse model. 750 MHz CW-EPR spectroscopy of C3H HeJ mice hind leg squamous cell tumour was performed after intra-venous tail vein injection of pH-sensitive nitroxide (R-SG) during stages of normal tumour growth, and in response to a single 10 Gy dose of X-ray irradiation. An inverse relationship was observed between tumour volume and pHe value, whereby during normal tumour growth a constant reduction in pHse was observed. This relationship was disrupted by X-ray irradiation, and from 2–3 days post exposure, a transitory increase pHe was observed. In this study we demonstrated the viability of CW-EPR spectroscopy using R-SG nitroxide to obtain high sensitivity pH measurements in mouse tumour model with accuracy < 0.1 pH units. In addition, measured changes in pHe in response to X-ray irradiation suggest this may offer a useful method for assessing physiological change in response to existing and novel cancer therapies.