Synthesis of polymers containing donor–acceptor Schiff base in side chain for nonlinear optics

The Schiff bases 4-(ω-hydroxyalkyloxy)-N-(5-nitro-2-thienylmethylene)aniline with 2, 6 and 8 methylenic units in their alkyl group in which a nitrothienyl group as acceptor and an oxyphenyl group as donor were synthesized by condensation of (ω-hydroxyalkyloxy)anilines with 5-nitro-2-thiophenecarboxaldehyde. The methacrylate monomers 4-(ω-methacryloyloxyalkyloxy)-N-(5-nitro-2-thienylmethylene)aniline with alkylene groups of different lengths were synthesized by two different routes and polymerized using a free radical initiator to produce low molecular weight polymers useful for nonlinear optics. All the obtained compounds were characterized by conventional spectroscopic methods. First-order hyperpolarizability (β) of 4-(2-hydroxyethyloxy)-N-(5-nitro-2-thienylmethylene)aniline typically was calculated using semiempirical method and the nonlinear optic properties of the same compound was studied by second harmonic generation.