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Amphiphilic diarylethene with tri(ethylene glycol) chains as a hydrophilic moiety and octylcarbamoyl chain as a hydrophobic moiety formed a supramolecular assembly by hydrophobic interactions in water. The closed-ring isomer formed bunched vesicles made of strongly curled bilayers. When methylcellulose was added to the suspension, sheets with a width of several hundred micrometers were mainly obtained by depletion force. The obtained sheets retained photoinduced shrinking character. [ABSTRACT FROM AUTHOR]

Photoinduced clustering of polystyrene microbeads and photocontrol of their diffusion was achieved in water with the assistance of photoinduced transformation of supramolecular architecture of amphiphilic diarylethene between sphere and fiber states. When a suspension of polystyrene beads containing the sphere state of diarylethene was UV-irradiated from beneath, clustering of the polystyrene beads by thermal convection was observed. The velocity of clustering was dependent on the amount of photogenerated nanofibers that determines the viscosity of the water. Diffusion of the clustered polymer beads was suppressed by the surrounding fibers, but was restored to regular Brownian motion upon irradiation with visible light. It was suggested that the diffusion of the microbeads was controlled by the transformation of aggregates between the more viscous fiber state and the less viscous sphere state. These results provide new insight into the photocontrol of particle motion in fluidic media. [ABSTRACT FROM AUTHOR]

Self-assembled microstructures of an amphiphilic diarylethene featuring an alkyl chain and triethylene glycol groups showed a photoinduced reversible morphological change in water. Reversible photoisomerization of the core diarylethene gave rise to a reversible morphological transformation between colorless microspheres and colored fibers. When colorless microspheres were irradiated with UV light, colored fibers were formed, and when the colored fibers were irradiated with visible light, the spheres were restored to their original positions where the spheres originally existed. This system showed reversible morphological change through not only photoirradiation but also temperature change. These behaviors can be interpreted as a phase transition between the sphere and fiber states. The dynamic process of the phase transition was monitored by polarized optical microscopy (POM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). It was revealed that the formation of fibers upon UV irradiation occurred radially at the surface of the sphere and the formation of the spheres upon visible-light irradiation occurred at the middle of the fiber. The unique photoinduced mechanical motion provides useful information for the design of sophisticated photoactuators. [ABSTRACT FROM AUTHOR]

A series of nitronyl nitroxide radicals having different lengths of phenylene ethynylene molecular wire were synthesized to investigate the decay constant of p-phenylene ethynylene. By the measurement and simulation of the ESR spectra of the biradicals, it was found that the exchange interaction decreased with a decay constant (β) of 0.39 Å-1 as the length of the molecule increased. This result indicates that the spin--spin exchange interaction between neutral radicals has a decay constant similar to that of the molecular conductance. This value of the decay constant indicates that a hopping mechanism does not take place in the measurement of the exchange interaction between neutral radicals even when the molecular wire has enough length to show hopping conduction of electrons. [ABSTRACT FROM AUTHOR]

Oligophenylene molecular rods with bicyclo[2.2.2]octane having two nitronyl nitroxide radicals were synthesized to investigate the decay constant of p-phenylene. By the measurement and simulation of the ESR spectra of the biradicals with different rod length, it was found that the exchange interaction was decreased with the decay constant β of 0.51 ± 0.01 Å−1. This result indicates that the spin−spin exchange interaction between neutral radicals has a decay constant similar to the molecular conductance. [ABSTRACT FROM AUTHOR]

Photocontrollable ambipolar transistors were developed by using diarylethene (DAE) layers with dibenzo[b,d]thiophene substituents as the transistor channels. An important feature is that both electron transport and hole transport occurred in the transistors upon ultraviolet (UV) light irradiation. The result indicates that the closed-ring isomer in the DAE molecules served as an ambipolar channel. Alternating UV and visible light irradiation controlled both the hole and electron currents, this was accompanied by photoisomerization from the closed-ring (semiconductor) to open-ring isomers (insulator). The light-induced on/off ratios in the drain currents were in the 95–225 range for the hole transport and in the 6–22 range for the electron transport. We found that the energy level alignment between the work function of the electrode and the molecular orbitals of the closed-ring isomer was responsible for the ambipolar transport. Our finding therefore offers a new strategy for developing optoelectronic organic transistors. [ABSTRACT FROM AUTHOR]