Photo-induced denitrogenation of triazoline moieties for efficient photo-assisted poling of electro-optic polymers

Abstract

Efficient room temperature poling of a guest–host electro-optic (EO) polymer is achieved by photo-induced denitrogenation of triazoline moieties. The host polymer (P1) with Δ2-1,2,3-triazoline groups on the backbone is synthesized by 1,3-dipolar cycloaddition polymerization between a bis-N-phenylmaleimide and an aromatic bis-azide. The guest chromophore (C1) is a push–pull compound with a strong dialkylaminophenyl donor and a CF3–TCF acceptor. By irradiating the thin films of P1 with a compact UV lamp at 365 nm, the angular and asymmetric 1,2,3-triazoline structures can be readily converted into a more straight and symmetrical aziridine structure by losing nitrogen. This photo-induced denitrogenation provides the clean conversion to form an aziridine-based polymer P2. This high efficiency conversion process is insensitive to the light-absorbing nonlinear optical chromophores, and the reaction rate can be controlled by the irradiation power and the thin film UV absorbance. Upon the photo-induced denitrogenation, considerable structural change of the polymer backbone provides sufficient rotational freedom to the chromophores for the poling of EO polymers. This has been verified by the demonstration of high field poling (up to 250 V μm−1) and large EO activity at RT for thin films containing 20–25 wt% of chromophore C1 in P1, which can be efficiently activated by photochemical denitrogenation of triazoline moieties by irradiating with low-power UV light.