title: Quantification of photoinduced order increase in liquid crystals with naphthopyran guests.
abstract: Photoinduced order-increasing phase transitions can occur in dye-liquid crystal mixtures when the photoproduct of the excitation of the dye molecules is more compatible with the liquid crystalline medium than the initial dye species. A detailed investigation of the photoinduced changes of the phase behavior and optical properties of mixtures of liquid crystals with naphthopyran guests upon exposure to light at 365 nm is presented here. In these guest-host systems, the nematic-to-isotropic phase transition temperature is increased upon irradiation. We show that the nematic range can be extended up to 2.9 °C by illumination in 5CB (4-n-pentyl-4'-cyanobiphenyl) liquid crystal mixtures. The order parameter is significantly increased by illumination at all temperatures within the nematic range and the changes are larger at higher concentrations of the guests. In particular, the illuminated guest-host mixtures exhibit order parameters close to those of the neat liquid crystal host at the same temperature relative to the clearing point. An improved understanding of the photophysical processes taking place at the molecular level in these material systems can inform the design of photoresponsive materials and enhance their potential utility in optical or photonic devices.
authors.affiliation: Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA.|Azimuth Corporation, 4027 Colonel Glenn Highway, Suite 230, Beavercreek, Ohio 45431, USA.
authors.forename: Mariacristina
authors.initials: M
authors.lastname: Rumi
authors.affiliation: Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA.|Azimuth Corporation, 4027 Colonel Glenn Highway, Suite 230, Beavercreek, Ohio 45431, USA.
authors.forename: Seth A
authors.initials: SA
authors.lastname: Cazzell
authors.affiliation: Alpha Micron Inc., 1950 State Route 59, Kent, Ohio 44240, USA.
authors.forename: Tamas
authors.initials: T
authors.lastname: Kosa
authors.affiliation: Alpha Micron Inc., 1950 State Route 59, Kent, Ohio 44240, USA.
authors.forename: Ludmila
authors.initials: L
authors.lastname: Sukhomlinova
authors.affiliation: Alpha Micron Inc., 1950 State Route 59, Kent, Ohio 44240, USA.
authors.forename: Bahman
authors.initials: B
authors.lastname: Taheri
authors.affiliation: Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: White
authors.affiliation: Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Bunning