Takayuki Ebata

Bio: Takayuki Ebata is an academic researcher from Tohoku University. The author has contributed to research in topics: Infrared spectroscopy & Spectroscopy. The author has an hindex of 40, co-authored 101 publications receiving 3877 citations.

Size‐selected vibrational spectra of phenol‐(H2O)n (n=1–4) clusters observed by IR–UV double resonance and stimulated Raman‐UV double resonance spectroscopies

Abstract: OH and CH stretching vibrations of bare phenol, phenol‐(H2O)n clusters (n=1–4), and partially deuterated clusters in the S0 state were observed by using IR–UV double resonance and stimulated Raman‐UV double resonance spectroscopies. Characteristic spectral features of the OH stretching vibrations of the phenol as well as of the H2O sites were observed, which are directly related to their structures. The cluster structures were investigated by comparing the observed spectra with the calculated ones obtained by the ab initio molecular orbital calculation with (self‐consistent field) SCF 6‐31G and SCF 6‐31G* basis sets given by Watanabe and Iwata. It was found that for the clusters with n≥2, the isomer of ring form hydrogen‐bonded structure is most stable and the simulated IR spectra based on the calculated structure showed good agreements with the observed ones. For a particular cluster, which was assigned as an isomer of the n=4 cluster, an anomalous IR spectrum was observed. Two forms of the isomer are proposed with respect to the structure of water moiety: (1) an ‘‘ice’’ structure and (2) an ‘‘ion‐pair’’ structure. The relative IR absorption cross sections of each bands were also investigated for the clusters with n=1 to 4. It was found that the IR absorption cross section of the phenolic OH stretching vibration of the n=1 cluster increases by a factor of 6 compared to that of bare phenol and it further increases with the cluster size.

Infrared Spectroscopy of Hydrogen-Bonded Phenol−Amine Clusters in Supersonic Jets

Abstract: We report infrared spectra of hydrogen-bonded phenol−amine clusters, phenol−NH3, −N(CH3)3, −NH(C2H5)2, and −N(C2H5)3, prepared in jet expansions. The OH, NH, and CH stretching fundamentals were studied. Infrared−ultraviolet double-resonance techniques were utilized for vibrational spectroscopy of size-selected clusters. The OH stretch frequencies of the phenol moieties showed extremely large red-shifts from that of bare phenol, reflecting the strong proton affinities of the amines. Moreover, non-proton-transferred structures of the clusters were confirmed. The detailed structure of phenol−NH3 was examined by ab initio calculations, which reproduced the observed infrared spectrum.

OH Stretching Vibrations of Phenol−(H2O)1 and Phenol−(H2O)3 in the S1 State

Abstract: OH stretching vibrations of phenol−(H2O)n clusters (n = 1, 3) in the S1 state have been observed by UV−IR double resonance spectroscopy, where the fluorescence dip induced by the IR excitation was monitored. The spectra were analyzed by comparing with those of the S0 state reported in a previous work. It was found that a frequency reduction of the phenolic OH stretching vibration and an enhancement of the interactions among the hydrogen bond network in the cluster were much larger in the S1 state than in the S0 state, representing the increase in acidity of phenol upon the electronic excitation. The nonradiative process of the vibrationally excited phenol is also discussed based on the fluorescence-dip spectrum of the deuterated phenol in S1.

Looking for Stable Carbenes: The Difficulty in Starting Anew

Abstract: A decade ago we initiated research, the goal of which was isolation of a stable carbene. Our success has helped to catalyze a resurgence of interest in readily available and easily handled carbenes. Research on stable (nucleophilic) carbenes is again a popular theme worldwide. Efforts in the general area of stable carbenes now focus not only on chemistry of the carbenes themselves but also on their applications to other chemical systems, where their chemical properties create technical opportunities that are unavailable with other functional groups. The quest for isolable carbenes is a long saga whose origin can be traced back to the first half of the 1800s. A recently published history of this quest provides an important backdrop for the research described in this Account.1 It is the intent of this Account to delineate the events and environment that led to the report from DuPont laboratories of the first isolation of a stable crystalline carbene. Getting Started

Excited-state hydrogen detachment and hydrogen transfer driven by repulsive 1πσ* states: A new paradigm for nonradiative decay in aromatic biomolecules

Abstract: The combined results of ab initio electronic-structure calculations and spectroscopic investigations of jet-cooled molecules and clusters provide strong evidence of a surprisingly simple and general mechanistic picture of the nonradiative decay of biomolecules such as nucleic bases and aromatic amino acids. The key role in this picture is played by excited singlet states of πσ* character, which have repulsive potential-energy functions with respect to the stretching of OH or NH bonds. The 1πσ* potential-energy functions intersect not only the bound potential-energy functions of the 1ππ* excited states, but also that of the electronic ground state. Via predissociation of the 1ππ* states and a conical intersection with the ground state, the 1πσ* states trigger an ultrafast internal-conversion process, which is essential for the photostability of biomolecules. In protic solvents, the 1πσ* states promote a hydrogen-transfer process from the chromophore to the solvent. Calculations for chromophore–water clusters have shown that a spontaneous charge-separation process takes place in the solvent shell, yielding a microsolvated hydronium cation and a microsolvated electron. These results suggest that the basic mechanisms of the complex photochemistry of biomolecules in liquid water can be revealed by experimental and theoretical investigations of relatively small chromophore–water clusters.