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Yuichi Terazono

Publications and source records attributed to Yuichi Terazono.

7 recordsLinked to original sources
PubMed2006

Conductance of a biomolecular wire.

Carotenoids (Car) act as "wires" that discharge unwanted electrons in the reaction center of higher plants. One step in this "side-path" electron conduction is thought to be mediated by Car oxidation. We have carried out direct measurements of the conductance of single-Car molecules under potential control in a membrane-mimicking environment, and we found that when Car are oxidized conductance is enhanced and the electronic decay constant (beta) is decreased. However, the neutral molecule may already be conductive enough to account for observed electron transfer rates.

Carotenoids↗
PubMed2006

Energy and photoinduced electron transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex.

Functional mimics of a photosynthetic antenna-reaction center complex comprising five bis(phenylethynyl)anthracene antenna moieties and a porphyrin-fullerene dyad organized by a central hexaphenylbenzene core have been prepared and studied spectroscopically. The molecules successfully integrate singlet-singlet energy transfer and photoinduced electron transfer. Energy transfer from the five antennas to the porphyrin occurs on the picosecond time scale with a quantum yield of 1.0. Comparisons with model compounds and theory suggest that the Förster mechanism plays a major role in the extremely rapid energy transfer, which occurs at rates comparable to those seen in some photosynthetic antenna systems. A through-bond, electron exchange mechanism also contributes. The porphyrin first excited singlet state donates an electron to the attached fullerene to yield a P(*+)-C(60)(*-) charge-separated state, which has a lifetime of several nanoseconds. The quantum yield of charge separation based on light absorbed by the antenna chromophores is 80% for the free base molecule and 96% for the zinc analogue.

Anthracenes↗
PubMed2005

Electronic decay constant of carotenoid polyenes from single-molecule measurements.

The conductance of carotenoid polyenes chemically bound at each end to gold contacts has been measured for single molecules containing 5, 7, 9, and 11 carbon-carbon double bonds in conjugation. The electronic decay constant, beta, is determined to be 0.22 +/- 0.04 A-1, in close agreement with the value obtained from first principles simulations (0.22 +/- 0.01 A-1). The absolute values of the molecular conductance are within a factor of 3 of those calculated from first principles. The small value of beta demonstrates that conductivity drops off only slowly with chain length, confirming that carotenoid conjugated chains are relatively good molecular "wires".

Journal Article↗
PubMed2004

Molecule-based photonically switched half-adder.

A molecule-based binary half-adder with optical inputs and outputs has been demonstrated. The half-adder consists of two photochromic organic molecules in solution and a third-harmonic-generating crystal. One substance acts as an AND Boolean logic gate and the other as an XOR gate. Inputs are laser pulses at 1064 or 532 nm that initiate photoisomerization reactions. Outputs are the optical absorbance of a fullerene radical anion (AND gate) and fluorescence of a porphyrin (XOR gate). The system carries out binary addition based on the laser input pulses. Half-adders in combination are capable of carrying out all mathematical operations necessary for digital computing.

Journal Article↗
PubMed2003

Synthesis and characterization of beta-trifluoromethyl-meso-tetraphenylporphyrins.

Beta-trifluoromethyl-meso-tetraphenylporphyrins were synthesized to investigate the electronic and steric effects of the trifluoromethyl groups on the macrocycle. Preparation of these novel porphyrins was carried out by copper-assisted trifluoromethylation of beta-tetrabromo-meso-tetraphenylporphyrin metal complexes and in situ generated CF3Cu. For comparison, the beta-methyl analogues were also prepared. Analysis of beta-trifluoromethylporphyrins by UV-vis, NMR, and cyclic voltammetry (CV) showed that the electron-withdrawing effects of the trifluoromethyl groups on the antipodal pyrroles required the macrocycle to take a fixed 18pi-electron pathway. UV-vis, CV, and molecular modeling studies suggest that the novel porphyrins are distorted following introduction of trifluoromethyl groups onto the pyrrolic beta-position of meso-tetraphenylporphyrin. The pK(a) difference of beta-tetrakis(trifluoromethyl)-meso-tetraphenylporphyrin from that of DBU in CH2Cl2, obtained by spectrophotometric titration, affirms that it is one of the most electron-deficient porphyrins so far prepared.

Journal Article↗
PubMed2002

Synthesis, crystal structures, and redox potentials of 2,3,12,13-tetrasubstituted 5,10,15,20-tetraphenylporphyrin zinc(II) complexes.

Zinc(II) complexes of antipodal beta-tetrasubstituted meso-tetraphenylporphyrin with trifluoromethyl (Zn(TPP(CF(3))(4)) (1a)), bromine (Zn(TPPBr(4)) (2a)), and methyl groups (Zn(TPP(CH(3))(4)) (3a)) were synthesized in order to examine the steric and the electronic effects of trifluoromethyl groups on the macrocycle. The analysis of X-ray crystal structures of the five-coordinate complexes Zn(TPP(CF(3))(4))(EtOH)(3) (1b), Zn(TPPBr(4))(MeOH)(DMF) (2b), and Zn(TPP(CH(3))(4))(THF)(1.6)(CHCl(3))(0.4) (3b) revealed distorted macrocyclic cores where significant differences in the Zn-N distance between the beta-substituted and the non-beta-substituted side were observed. The difference was significant in 1b due to the strong steric interactions among the peripheral substituents and the electronic effects of trifluoromethyl groups. The macrocycles of 1b-3b are saddle-distorted and slightly ruffled due to the five-coordination of zinc(II) and the peripheral substitution. Distortion of the macrocycles of 2b and 3b were modest. On the other hand, distortion in 1b was severe due to the peripheral strain. Cyclic voltammetric measurements of the four-coordinate complexes Zn(TPP) and 1a-3a were performed and their redox potentials were analyzed together with previously reported potentials of Zn(TPP(CN)(4)). The oxidation potential of 1a did not gain as much as expected from the electron-withdrawing effect of the four trifluoromethyl groups. The HOMO-LUMO gap of 1a was very small (1.5 V) and cannot just be explained by macrocyclic distortion. The magnitude of this gap is very similar to that of Zn(TPP(CN)(4)). Compound 2a also exhibited a modest gap contraction. Compound 3a was easier to oxidize and harder to reduce than Zn(TPP), even though the HOMO-LUMO gap of 3a was similar to that of Zn(TPP).

Journal Article↗