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The mechanism for negative photochromism of spiropyran in silica was investigated. Prior to our study, the chemical origin of the high thermal stability of the photomerocyanine form (PMC-form) dispersed in perhydropolysilazane (PHPS), which is converted to silica at ambient temperature, had been investigated. The high thermal stability of the PMC-form is attributed to the protonated PMC-form (HÁÁÁPMC-form), which is produced by intermolecular hydrogen bonding between oxide anions generated by the cleavage of the C À O bonds and the partially uncondensed Si À OH and O À H bonds of silica. Furthermore, the HÁÁÁPMC-form could be thermally isomerized from the SPform without UV light irradiation. This specific phenomenon is caused by the so-called negative photochromism. In this study, we proposed a mechanism for negative photochromism according to the relationship of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The relationship between the HOMOs was determined using cyclic voltammetry (CV) and ultraviolet photoelectron spectroscopy (UPS). On the other hand, the relationship between the LUMOs was determined from the respective optical bandgap. As a result, the HOMO level of HÁÁÁPMC-form was À6.1 eV and that of SP-form was À5.3 eV. Accordingly, the thermodynamic stabilization of HÁÁÁPMC-form was attributed to the thermal isomerization through negative photochromism from the SP-form.

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We have carried out the photoemission study of various alkanethiolate-͑AT-͒ passivated Au nanoparticles. From the detailed line-shape analyses of Au 4f core-level photoemission spectra, it is found that the interface chemical states are independent on the surface passivants of AT molecules among the AT-passivated Au nanoparticles with the same size. Moreover, the interface electronic structures of AT-passivated Au nanoparticles have been characterized. It is found that the surface-potential shifts due to the interface dipoles accompanying the adsorption of AT molecules are about 0.36 eV and are independent on the surface passivants of AT molecules. The detailed interface electronic state of AT-passivated Au nanoparticle is discussed.

The energy band-lineup and the electronic structure of NO2-exposed H-terminated diamond/Al2O3 heterointerface have been investigated by synchrotron radiation photoemission and x-ray absorption near-edge structure (XANES) measurements. It is found that the energy band-lineup is stagger-type, so-called type-II, with its valence band discontinuity of as high as 3.9 eV and its conduction band discontinuity of 2.7 eV. The valence band maximum of the H-terminated diamond surface is positioned at Fermi level as a result of high-density hole accumulation on the diamond side. The XANES measurement has shown that the oxygen-derived interface state locates at about 1–3 eV above the Fermi level.