title: Phototropic Guest-Host Liquid Crystal Systems: Environmental Effects on Naphthopyran Kinetics.
abstract: Photoinduced isothermal and order-increasing phase transitions can be observed in guest-host liquid crystal mixtures containing naphthopyran derivatives. The changes are attributed to the different geometry and a less energetically favorable interaction with the liquid crystal molecules for the ground state naphthopyran species with respect to the photoproduct. In this study, we have investigated the thermal relaxation of the naphthopyran photoproduct back to the initial species as a function of temperature and excitation conditions. It was found that the thermal relaxation is typically first-order and its characteristic rate has a temperature dependence that is different in the anisotropic and isotropic states of the mesogenic solvents. In particular, the activation energy for thermal relaxation is larger in the ordered phases of mesogenic solvents relative to their isotropic phase. The findings suggests that the naphthopyran relaxation is hindered by the organization of the host environment. These results will be useful to build a more complete understanding of the mutual guest-host interactions in naphthopyran-containing guest-host LC systems.
authors.affiliation: Materials and Manufacturing Directorate, Air Force Research Laboratory , Wright Patterson Air Force Base, Ohio 45433, United States.|Azimuth Corporation , 4027 Colonel Glenn Highway, Suite 230, Beavercreek, Ohio 45431, United States.
authors.forename: Mariacristina
authors.identifier: 0000-0002-4597-9617
authors.initials: M
authors.lastname: Rumi
authors.affiliation: Materials and Manufacturing Directorate, Air Force Research Laboratory , Wright Patterson Air Force Base, Ohio 45433, United States.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: White
authors.affiliation: Materials and Manufacturing Directorate, Air Force Research Laboratory , Wright Patterson Air Force Base, Ohio 45433, United States.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Bunning