Ultrahigh-temperature polymers for second-order nonlinear optics. Synthesis and properties of robust, processable, chromophore-embedded polyimides

A general, convergent approach to the synthesis of a series of stilbene- and azo-based donor-acceptor, second-order nonlinear optical (NLO) chromophores is reported. The synthetic strategy enables preparation of both acid- and base-reactive structures, yielding protected, diamine-functionalized chromophores which can be liberated using either acidic or alkaline regents for incorporation into polyimide backbones. Three such chromophores, bis(4-aminophenyl)[4-(2-(4-nitrophenyl)vinyl)phenyl]amine, bis(4-aminophenyl)[4-(2-(6-nitrobenzothiazol-2-yl)vinyl)phenyl]amine, 2-[4-((4-(bis(4-aminophenyl)amino)phenyl)diazenyl)phenyl]-2-phenyl-1,1-dicyan oethylene, all having high thermal stabilites, were synthesized, characterized, and condensed with hexafluoroisopropylidene diphthalic anhydride or 2-(1,3-dioxoisobenzofuran-5-ylcarbonyloxy)ethyl 1,3-dioxoisobenzofuran-5-carboxylate to yield six high glass transition temperature polyimides (T(g) as high as 313 °C) for use as poled NLO materials. After casting as thin films, curing, and electric field corona poling, these materials exhibit χ((2)) (1064 nm) responses as high as 82.0 pm/V and negligible decay in response upon aging in air at 100 °C for over 1000 h.