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Influence of Excitation Transfer on the All-optical Orientation of Fluorescent Chromophores in Polymers
Sebastien Bidault, Sophi Brasselet, Veronique Le Floch and Joseph Zyss

We use polarized two-photon fluorescence as a probe for optically induced anisotropies in polymer films. All-optical orientation provided by mutiphotonic interaction is performed in guest-host polymers containing multifunctional chromophores with fluorescent, photoisomerizable and nonlinear properties. Polarization-resolved two-photon fluorescence measurements are a convenient tool to explore the even order parameters of the molecular orientational distribution after orientation, with, in addition, a high sensitivity to inter-molecular interactions. In the case of high concentration polymers, we show that the excitation transfer between chromophores strongly influences the two-photon fluorescence polarization response of optically poled areas, resulting in a loss of anisotropy and polarization-sensitivity. Through polarization-resolved optical poling experiments conducted on polymer films doped with various concentrations of a dye laser (DCM), we investigate the competition between the different non-radiative processes such as excitation transfer and photochemical mechanisms involved in the molecular orientation.

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