Tuyoshi Fukaminato

Organic chemistry: A digital fluorescent molecular photoswitch

Fluorescent properties can be useful not only for tracking individual molecules within a microenvironment, but also in molecular-scale opto-electronics. Here we use external photostimulation to switch the fluorescence on and off from a single photochromic molecule embedded in a polymer film. This digital response is due to photo-isomerization of the molecule, which may eventually find application in erasable optical data-storage elements.

Photochromism of diarylethene molecules and crystals: Memories, switches, and actuators

Switches, and Actuators Masahiro Irie,*,† Tuyoshi Fukaminato,‡ Kenji Matsuda, and Seiya Kobatake †Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku, Tokyo 171-8501, Japan ‡Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020, Japan Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan

Molecular Design Strategy toward Diarylethenes That Photoswitch with Visible Light

Photoactive molecules that reversibly switch upon visible light irradiation are one of the most attractive targets for biological as well as imaging applications. One possible approach to prepare such photoswitches is to extend π-conjugation length of molecules and shift the absorption bands to longer wavelengths. Although several attempts have been demonstrated based on this approach for diarylethene (DAE) photoswitches, photoreactivity of the DAE derivatives is dramatically suppressed when the conjugation length is extended by connecting aromatic dyes at the side positions of aryl groups in the DAE unit. In this study, we successfully prepared a visible-light reactive DAE derivative by introducing an aromatic dye at the reactive carbon atom of the DAE unit, optimizing orbital level of each component, and controlling the mutual orientation of the aromatic dye and the DAE unit. The DAE derivative (3) undergoes a photocyclization reaction upon irradiation with 560 nm light and the closed-isomer converts to the open-ring isomer upon irradiation with 405 nm light. The high photoconversion yields (>90%) were achieved for both photocyclization and photocycloreversion reactions. The photoreactivity induced by visible light irradiation and the molecular design strategy were discussed based on theoretical calculations.

Fluorescence photoswitching of a diarylethene–perylenebisimide dyad based on intramolecular electron transfer

A fluorescent photochromic molecule, which is composed of a photochromic diarylethene (DE) and a fluorescent perylenebisimide (PBI), was synthesized and its fluorescence photoswitching was studied. The fluorescence quantum yield of the open-ring isomer is constant irrespective of solvent polarity, while that of the closed-ring isomer decreases with an increase in the dielectric constant of solvents. Femtosecond time-resolved transient and fluorescence lifetime measurements revealed that the fluorescence quenching of the closed-ring isomer is attributed to the intramolecular electron transfer from the PBI chromophore to the DE unit.

Perylenebisimide-linked nitroxide for the detection of hydroxyl radicals

A new type of fluorophore-linked nitroxide for the detection of hydroxyl radical (OH) was synthesized using perylene-3,4,9,10-tetracarboxyl bisimide and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). This new fluorescent probe, indicated here as Spy-OH (swallow-tailed perylene derivative for detecting OH) has its natural fluorescence effectively reduced due to the quenching caused by the presence of the nitroxide radical in its structure. In the presence of OH, in media containing DMSO, a conspicuous increase in the fluorescence intensity was observed. No significant change in the fluorescence intensity was observed upon the addition of other several reactive oxygen species (ROS) except for OH. Spy-OH maxima excitation (lambda(exc)) and emission (lambda(em)) wavelengths lie in the visible region (520/530 nm), therefore, this fluorescent probe is expected to be useful for a simple and selective detection of OH, especially for biosamples.

Invisible photochromism of diarylethene derivatives

Diarylethene derivatives with oxidized thiophene rings shift their absorption band to a shorter wavelength in the UV region upon photocyclization; no color change was observed during the photochromic reaction, and the invisible photochromism is advantageous for devices used under room light.

Complete ON/OFF photoswitching of the motility of a nanobiomolecular machine.

To apply motor proteins as natural nanomolecular machines to transporting systems in nanotechnology, complete temporal control over ON/OFF switching of the motility is necessary. We have studied the photoresponsive inhibition properties of azobenzene-tethered peptides for regulation of kinesin-microtubule motility. Although a compound containing a peptide having an amino acid sequence derived from the kinesins C-terminus (a known inhibitor of kinesins motor domain) and also featuring a terminal azobenzene unit exhibited an inhibition effect, the phototunability of this behavior upon irradiation with UV or visible light was only moderate. Unexpectedly, newly synthesized peptides featuring the reverse sequence of amino acids of the C-terminus of kinesin exhibited excellent photoresponsive inhibition. In particular, azobenzene-CONH-IPKAIQASHGR completely stopped and started the motility of kinesin-microtubules in its trans- and cis-rich states, respectively, obtained after irradiation with visible and UV light, respectively. A gliding motility system containing this photoresponsive inhibitor allowed in situ control of the motion of microtubules on a kinesin-coated glass substrate. It is expected that the present results on the photoresponsive nanomotor system open up new opportunities to design nanotransportation systems.

Photocyclization reaction of a diarylmaleimide derivative in polar solvents

Photochromism of a symmetric diarylmaleimide derivative, having two thiophene rings (1), and a non-symmetric derivative having a S,S-dioxide thiophene ring and a thiophene ring (2) as the aryl moieties, was studied in various solvents. The photocyclization quantum yield of gradually decreased with increasing the solvent polarity and the reaction was not observed in polar solvents, such as ethanol and acetonitrile; on the other hand, such a strong solvent dependence of the photocyclization reaction was not observed for ; the different behavior is attributed to the weaker electron donating ability of the S,S-dioxide thiophene ring.

Raman spectroscopic study on photochromic reaction of a diarylethene derivative

Abstract Photochromic reaction of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene has been studied by FT-Raman spectroscopy. The Raman bands in the 1300–1700 cm −1 region of the open-ring isomer of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene are clearly distinguished from those of the closed-ring isomer. The vibrational assignment has been made by measuring the polarized Raman spectrum and density functional theory calculations at the B3LYP/6-31G** level.

Dynamic Photocontrol of the Gliding Motility of a Microtubule Driven by Kinesin on a Photoisomerizable Monolayer Surface

The gliding motility of microtubules driven by kinesin on the surface of an azobenzene monolayer presenting lysine terminal groups is reversibly and repeatedly altered upon photoisomerization of the monolayer.