Photochromic chiral liquid crystalline systems containing spiro-oxazine with a chiral substituent II. Photoinduced behaviour

The photoinduced behaviour of low molecular mass liquid crystalline (LC) sy stems doped with the chiral photochromic spiro-oxazine, 9'-{5-(-)-menthoxya cetoxy-1,3-dihydro-1,3,3-trimethylspiro [2H-indole-2,3'-[3H]naphth-[2.1-b][ 1,4]oxazine]} 4-[11-(tetrahydro-2-pyranyloxy)undecyloxy] biphenyl-4'-carbox ylate (THP11SOM) was observed by means of transmittance measurements at 21 degreesC. The experimental results revealed that the ring-opened merocyanin e form of THP11SOM resulting from the photochromism first disturbed the hel ical planar orientation of the LC molecules and then induced a new helical pitch. The magnitudes of both the disturbance in orientation of the LC mole cules and the shift in the helical pitch were significantly influenced by t he concentration of THP11SOM. The photoinduced behaviour was reversible due to the photochemical and thermal back reaction of the THP11SOM. In additio n, the effect of UV light on the nematic-isotropic transition temperatures of the mixtures with or without a hindered amine light stabilizer was studi ed.