Abstract

An organic soluble polyimide was prepared from 3,3′-dihydroxybenzidine and 2,2-bis(phthalic anhydride)hexafluoropropane. The two hydroxy groups in the repeating unit of the polyimide thus prepared were utilized in attaching 4-nitro-4′-diphenylaminoazobenzene chromophores onto the main chain perpendicularly (or in an end-on fashion) or laterally (or in a side-on fashion) through either the oxydimethylene or oxyhexamethylene spacer. All the polymers revealed two strong absorptions: one λ_max at 300 nm and the other λ_max at 493 nm. The polymers, when electrically poled, showed 2^nd order nonlinear optical properties, r₃₃ = 9–23 pm V⁻¹ at 1300 nm, r₃₃ = 102–194 pm V⁻¹ at 633 nm, and d₃₃ = 59–109 pm V⁻¹ at 1064 nm depending on their structure. The polymers bearing side-on attached chromophores revealed higher r₃₃ values than those with end-on attached chromophores. Temporal stability of the former was also greater than that of the latter.