Sensitized photochemical switching for cholesteric liquid crystal displays
View Patent ↗The present invention relates to photo-tunable dopant compositions comprising a photo-reactive chiral compound capable of undergoing a photochemical reaction resulting in the loss of chirality, and a triplet sensitizer. The present invention also relates to a display comprising a substrate, a liquid crystalline layer thereon, wherein the liquid crystalline layer comprises a nematic host, at least one chiral dopant, a photo-reacted compound, and a triplet sensitizer, and at least one transparent conductive layer. The present invention also relates to a method of tuning a cholesteric liquid crystal material comprising providing at least one mesogenic compound, at least one triplet sensitizer, and at least one photo-reactive chiral compound; combining the at least one mesogenic compound, at least one triplet sensitizer, and at least one photo-reactive chiral compound to form a mixture; and irradiating the mixture for a period of time.
1. A photo-tunable dopant composition comprising a photo-reactive chiral compound, wherein said photo-reactive chiral compound is capable of undergoing a photochemical reaction resulting in the loss of the chirality of said photo-reactive chiral compound, and a triplet sensitizer, wherein said photochemical reaction is triplet sensitization resulting in racemization and/or isomerization, and wherein said photo-reactive chiral compound is selected from the group consisting of:
PTCD-1
PTCD-2
PTCD-3
PTCD-4
PTCD-5
PTCD-6
PTCD-7
PTCD-8
PTCD-9
PTCD-10
PTCD-11
2. The photo-tunable dopant composition of claim 1 wherein said photo-reactive chiral compound is:
PTCD-1
3. The photo-tunable dopant composition of claim 1 wherein said photo-reactive chiral compound is:
PTCD-3
4. The photo-tunable dopant composition of claim 1 wherein said photo-reactive chiral compound is:
PTCD-5
5. The photo-tunable dopant composition of claim 1 wherein said 5 photo-reactive chiral compound is:
PTCD-8
6. The photo-tunable dopant composition of claim 1 wherein said photochemical reaction is decomposition resulting in triplet sensitization bond cleavage reaction.
7. The photo-tunable dopant composition of claim 6 wherein said bond cleavage reactions affect photoremovable protecting groups or photocleavable leaving groups.
8. The photo-tunable dopant composition of claim 7 wherein said photoremovable protecting groups are esters of sulfonic acids, carboxylic acids, hydrazones, aryl azido ethers, benzoin esters, or benzyloxycarbonyl compounds.
9. The photo-tunable dopant composition of claim 7 wherein said photocleavable leaving groups are aryl cyano acids, aryloxy acetic acids, u-aryl propionic acids, or benzoin esters.
10. The photo-tunable dopant composition of claim 7 wherein said photocleavable leaving groups are aryl ketones.
11. The photo-tunable dopant composition of claim 1 further comprising at least one non-photo-tunable chiral dopant.
12. The photo-tunable dopant composition of claim 11 wherein said at least one non-photo-tunable chiral dopant is isosorbide, isomannide ester, TADDOL derivative, or spiroindane ester.
13. The photo-tunable dopant composition of claim 11 wherein said photo-tunable chiral dopant and said non-tunable chiral dopants have opposite twist sense.
14. The photo-tunable dopant composition of claim 1 wherein, when the lowest triplet energy of said photo-reactive chiral compound is higher than the lowest triplet energy of said triplet sensitizer, said lowest triplet energy of the photo-reactive chiral compound is no greater than 6 kcal greater than said lowest triplet energy of said triplet sensitizer.
15. The photo-tunable dopant composition of claim 1 wherein the lowest triplet energy of said photo-reactive chiral compound is lower than the triplet energy of said triplet sensitizer.
16. The photo-tunable dopant composition of claim 1 wherein said triplet sensitizer comprises from 0.002 to 20% by weight of the photo-tunable chiral dopant.
17. The photo-tunable dopant composition of claim 1 wherein said triplet sensitizer is covalently attached to said photo-reactive chiral compound.
18. The photo-tunable dopant composition of claim 1 wherein said triplet sensitizer comprises thioxanthone.
19. The photo-tunable dopant composition of claim 18 wherein said triplet sensitizer is:
S-1
20. The photo-tunable dopant composition of claim 18 wherein said triplet sensitizer is:
S-2
21. The photo-tunable dopant composition of claim 1 wherein said triplet sensitizer comprises ketocoumarin.
22. The photo-tunable dopant composition of claim 21 wherein said triplet sensitizer is:
S-2
23. The photo-tunable dopant composition of claim 21 wherein said triplet sensitizer is:
S-7
24. The photo-tunable dopant composition of claim 1 wherein said triplet sensitizer comprises at least one member selected from the group consisting of xanthones, thioxanthones, chlorothioxanthones, arylketones and polycyclic aromatic hydrocarbons.
25. The photo-tunable dopant composition of claim 1 wherein said triplet sensitizer absorbs light above 400 nm.
26. The photo-tunable dopant composition of claim 1 wherein said triplet sensitizer is selected from the group consisting of:
S-1
S-2
S-3
S-4
S-5
S-6
S-7
S-8
S-9
S-10
S-11
S-12
S-13
S-14
S-15
S-16
S-17
S-18
S-19
S-20
S-21
S-22
27. The photo-tunable dopant composition of claim 1 further comprising at least one cosensitizer.
28. The photo-tunable dopant composition of claim 27 wherein said cosensitizer has a triplet energy in the range of from 45 to 72 kcal/mole.
29. The photo-tunable dopant composition of claim 1 further comprising a nematic host.