Light-induced liquid crystallinity.

Nature 2012 May 16;485(7398):347-9. Epub 2012 May 16.

Alpha Micron Inc., Kent, Ohio 44240, USA.

Liquid crystals are traditionally classified as thermotropic, lyotropic or polymeric, based on the stimulus that governs the organization and order of the molecular system. The most widely known and applied class of liquid crystals are a subset of thermotropic liquid crystals known as calamitic, in which adding heat can result in phase transitions from or into the nematic, cholesteric and smectic mesophases. Photoresponsive liquid-crystal materials and mixtures can undergo isothermal phase transitions if light affects the order parameter of the system within a mesophase sufficiently. In nearly all previous examinations, light exposure of photoresponsive liquid-crystal materials and mixtures resulted in order-decreasing photo-induced isothermal phase transitions. Under specialized conditions, an increase in order with light exposure has been reported, despite the tendency of the photoresponsive liquid-crystal system to reduce order in the exposed state. A direct, photo-induced transition from the isotropic to the nematic phase has been observed in a mixture of spiropyran molecules and a nematic liquid crystal. Here we report a class of naphthopyran-based materials that exhibit photo-induced conformational changes in molecular structure capable of yielding order-increasing phase transitions. Appropriate functionalization of the naphthopyran molecules leads to an exceedingly large order parameter in the open form, which results in a clear to strongly absorbing dichroic state. The increase in order with light exposure has profound implications in optics, photonics, lasing and displays and will merit further consideration for applications in solar energy harvesting. The large, photo-induced dichroism exhibited by the material system has been long sought in ophthalmic applications such as photochromic and polarized variable transmission sunglasses.

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature11122DOI Listing
May 2012
10 Reads

Publication Analysis

Top Keywords

phase transitions
16
light exposure
12
liquid crystals
12
photoresponsive liquid-crystal
12
materials mixtures
8
liquid-crystal materials
8
isothermal phase
8
order parameter
8
increase order
8
order light
8
order
6
phase
5
crystal report
4
liquid crystal
4
spiropyran molecules
4
molecules nematic
4
nematic liquid
4
materials exhibit
4
changes molecular
4
molecular structure
4

References

(Supplied by CrossRef)

P Collings et al.
1997

T Ikeda et al.
Science 1995

F Ortica et al.
Photochem. Photobiol. Sci. 2002

SK Prasad et al.
Adv. Mater. 2005

SK Prasad et al.
J. Phys. Chem. B 2007

SV Serak et al.
J. Nonlinear Opt. Phys. Mater. 2007

B Zalar et al.
Phys. Rev. E 2000

S Kurihara et al.
J. Chem. Soc. Faraday Trans. 1991

M Maafi et al.
Int. J. Chem. Kinet. 2005

M Frigoli et al.
Chem. Commun. 2004

L Shragina et al.
Liq. Cryst. 1990

Similar Publications