Shogo Yamane

Mechanochromic luminescent liquid crystals based on a bianthryl moiety

Smectic liquid crystals consisting of an aromatic moiety based on 10,10′-bis(phenylethynyl)-9,9′-bianthryl at the central part and one and two mesogenic moieties on each side connected through oxyethylene spacers have been prepared to develop stimuli-responsive materials. The compound having two mesogenic moieties on each side (i.e. four total) forms an ordered smectic phase. Mechanochromic luminescence is observed for the smectic liquid crystal. A sample of this molecule formed by thermal annealing shows green photoluminescence at room temperature. The photoluminescent color changes from green to blue-green with mechanical stimulation at room temperature. The change of the photoluminescent color by mechanical shearing is ascribed to the disturbance of the π–π interactions between the adjacent molecules. Moreover, the original green photoluminescent color is recovered by heating followed by cooling to room temperature. The effects of the number, and thus volume of mesogenic moieties were also examined. Smaller mesogenic moieties lead to stronger ground state interactions between adjacent luminescent molecules and red-shifted emission. In contrast, the compound having three mesogenic moieties on each side shows no mechanochromic luminescence. The large mesogenic moieties disturb intermolecular interactions, resulting in no detectable change in the assembled structure of luminescent moieties upon mechanical stimulation. These results suggest that the present molecular design is useful for fabricating new stimuli-responsive materials with liquid-crystalline behavior.

Mechanoresponsive liquid crystals exhibiting reversible luminescent color changes at ambient temperature

Mechanochromic luminescent liquid crystals containing oligothiophene derivatives have been obtained. These liquid-crystalline (LC) molecules having bi-, ter-, and quarterthiophene moieties exhibit shear-induced phase transitions accompanied by changes in their luminescent colors at ambient temperature. The shear-induced LC phases and their luminescent colors spontaneously revert back to the initial LC phases and the initial luminescent colors during the thermal aging processes at ambient temperature because the shear-induced LC phases are metastable phases. These three compounds show various luminescent colors and cover a wide visible region. The terthiophene and quaterthiophene derivatives recover their initial luminescent colors faster than the bithiophene derivative, indicating that not only the luminescent colors but also the stimuli-responsive properties are tunable through simple change of the π-conjugated length of the luminescent mesogen.

Stimuli-responsive photoluminescent liquid crystals.

We describe mechanochromic and thermochromic photoluminescent liquid crystals. In particular, mechanochromic photoluminescent liquid crystals found recently, which are new stimuli-responsive materials are reported. For example, photoluminescent liquid crystals having bulky dendritic moieties with long alkyl chains change their photoluminescent colors by mechanical stimuli associated with isothermal phase transitions. The photoluminescent properties of molecular assemblies depend on their assembled structures. Therefore, controlling the structures of molecular assemblies with external stimuli leads to the development of stimuli-responsive luminescent materials. Mechanochromic photoluminescent properties are also observed for a photoluminescent metallomesogen and a liquid-crystalline polymer. We also show thermochromic photoluminescent liquid crystals based on origo-(p-phenylenevinylene) and anthracene moieties and a thermochromic photoluminescent metallocomplex.

Mechanochromic Photoluminescent Liquid Crystals Containing 5,5′-Bis(2-phenylethynyl)-2,2′-bithiophene

5,5′-Bis(2-phenylethynyl)-2,2′-bithiophene derivative 1 containing dendritic moieties linked through amide groups was synthesized. Compound 1 exhibits a rectangular columnar phase on slow cooling from the isotropic liquid. In contrast, a cubic phase is formed as a metastable liquid-crystalline phase by rapid cooling of the isotropic melt. Mechanical shearing induces a cubic–columnar phase transition, accompanied by the change of a photoluminescent color from yellow-green to green. The infrared spectra of 1 suggest that the mechanical stimuli can induce the partial dissociation of the hydrogen bond. This may lead to more disordering of the π-stacks of chromophores.

High‐resolution MALDI‐TOF MS study on analysis of low‐molecular‐weight products from photo‐oxidation of poly(3‐hexylthiophene)

High-resolution matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (TOF MS) was used for the analysis of the low-molecular-weight products from the photo-oxidation of poly(3-hexylthiophene) (P3HT) in solution and thin film. Eight new peak series were observed in the low-mass range of the mass spectra of the products degraded in solution, and the formulas of the eight components were determined from the accurate mass. From SEC/MALDI-TOF MS, two components were identified as the degraded products, and the other six components were derived from the fragmentation of the degraded products during the MALDI process. A mechanism for the formation of these components was proposed on the basis of the results of MALDI-TOF MS. For the thin film degradation, a part of products in the solution degradation were observed, which supports that the oxidation of P3HT in solution and thin film proceeded in the same mechanism. This study shows that high-resolution MALDI-TOF MS is effective for the analysis of the low-molecular-weight products from P3HT photo-oxidation and expected to be feasible for the degradation analyses of other polymers. Copyright