Dynamic photoswitching of helical inversion in liquid crystals containing photoresponsive axially chiral dopants.

Chirality switching is intriguing for the dynamic control of the electronic and optical properties in nanoscale materials. The ability to photochemically switch the chirality in liquid crystals (LCs) is especially attractive given their potential applications in electro-optic displays, optical data storage, and the asymmetric synthesis of organic molecules and polymers. Here, we present a dynamic photoswitching of the helical inversion in chiral nematic LCs (N*-LCs) that contain photoresponsive axially chiral dopants. Novel photoresponsive chiral dithienylethene derivatives bearing two axially chiral binaphthyl moieties are synthesized. The dihedral angle of the binaphthyl rings changes via the photoisomerization between the open and closed forms of the dithienylethene moiety. The N*-LCs induced by the dithienylethene derivatives that are used as chiral dopants exhibit reversible photoswitching behaviors, including a helical inversion in the N*-LC and a phase transition between the N*-LC and the nematic LC. The present compounds are the first chiral dopants that induce a helical inversion in N*-LC via the photoisomerization between open and closed forms of the dithienylethene moiety.

Gelastic seizure with hypothalamic hamartoma: proton magnetic resonance spectrometry and ictal electroencephalographic findings in a 4-year-old girl.

Gelastic seizure is a rare symptom often associated with hypothalamic hamartoma. We present here a 4-year-old girl with gelastic epilepsy caused by hypothalamic hamartoma and report the magnetic resonance spectrometry and electroencephalographic (EEG) findings. At the age of 2 1/2 years, she developed brief, repetitive laughing attacks or mixed attacks with laughing and crying, which were refractory to carbamazepine. An interictal EEG showed intermittent slow waves in the left frontocentral region and sporadic positive sharp waves in the left centroparietal area. Ictal EEG demonstrated dysrhythmic theta activity in the left central area 3 seconds after the onset of laughing. Brain magnetic resonance imaging demonstrated a large sessile mass, isointense to gray matter, in the region of the hypothalamus, suggesting hypothalamic hamartoma. Proton magnetic resonance spectrometry of the hypothalamic hamartoma revealed a significant reduction of the N-acetylaspartate/serum creatinine ratio. The altered chemical shift imaging with magnetic resonance spectrometry in our patient suggests a biochemical abnormality in the tissue of the hypothalamic hamartoma. Moreover, this abnormal function of the hamartoma tissue might be closely related to epileptogenesis because the time difference between the ictal laughter and the subsequent EEG changes in the ictal EEG does not support the idea that the activated cortex is the epileptogenic focus.

Photochemically colour-tuneable white fluorescence illuminants consisting of conjugated polymer nanospheres.

π-Conjugated aromatic polymers have attracted much interest due to their semi-conducting and luminescent properties, and are therefore regarded as promising materials for next-generation optoelectronic devices. Especially, it is considered as one of the indispensable steps for advanced function to control the optoelectronic properties by external stimuli. Herein, we show photochemically fluorescent colour-tuneable systems consisting of photoresponsive conjugated polymer nanospheres. We design and synthesize photoresponsive conjugated polymers with red, green and blue (RGB) fluorescence by introducing photoisomeric dithienylethene moieties in the side chains. A mixture of the red-, green- and blue-fluorescent polymer nanospheres exhibits photoswitchable white fluorescence between emission and quenching by irradiating external lights in both the nanosphere solution and film state. In addition, reversible change in fluorescent colour between white and RGB is also achieved by replacing a photoresponsive polymer with a non-photoresponsive analogue in the mixture. Thus, we successfully demonstrate 'photoresponsive polymer illuminant' systems bearing photochemically colour-tuneable white fluorescence.