Development of molecular spectroscopy with the use of femtosecond light pulses in the near-infrared spectral region

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1. Formation of charge-transfer state in bianthrylBianthryl is formed by two anthracene rings connected by a C-C bond. When this molecule absorbs a photon, an electron is migrated from one of the anthracene rings to the other. This is one of the most basic and simplest chemical reactions. By using femtosecond time-resolved near-infrared spectroscopy, the locally excited (LE) state and the charge transfer (CT) state are clearly observed as separate transitions. It has been concluded that the LE state generated by the photoirradiation of bianthryl in acetonitrile solution is directly converted to the CT state.2.Carrier dynamics in titanium oxideBecause the wavelength of the probe light is longer than visible or ultraviolet spectroscopies, it is possible to apply time-resolved near-infrared spectroscopy to scattering samples with the transmission method. By using this advantage, the head investigator and his collaborators have applied femtosecond time-resolved near-infrared spectroscopy t … More o the powder samples of titanium oxide photocatalyst (TIO4, 20 nm in diameter). They successfully observed an electron relaxation process that occurs within 1 ps, electro-hole recombination processes in several tens of picoseconds, and an electron migration process from titanium oxide to platinum co-catalyst in 2 ps. The results explain the mechanism of the increase of catalytic activities when platinum co-catalyst is loaded to titanium oxide particles.3.Nature of charge-transfer state of symmetrically and asymmetrically substituted bianthrylsTime-resolved near-infrared spectra of symmetrically and asymmetrically substituted bianthryls have been measured. CT state absorption bands in the near-infrared region were observed only for the symmetrically substituted bianthryls ; they were not observed for the asymmetrically substituted bianthryls. It is strongly suggested that the CT absorption band observed in the near-infrared region represents the charge resonance interaction between the two anthracene rings. Less