Effects of main chains on the second order nonlinear optical susceptibility of poled poly(dipropargyloxybenzoates) containing 2-[4-(2-chloro-4-nitrophenylazo)-N-ethyl-phenylamino]ethanol (Disperse Red 13)

A series of isomeric polymers containing hexa-2,4-diynylene-1,6-dioxybenzoate group as the main chain and a polar azo dye (Disperse Red 13) as in the side chain were synthesized, and their second order nonlinear optical responses were studied. The second order nonlinear coefficients, d33 were found to be in the range of 50–90 pm/V. The nonlinear response (d33) with respect to the positions of main chain was found to be in the order; 3,5-(meta) > 3,4-(ortho) > 2,5- (para) > 2,4-(meta), but the order of values d33/d31 was 3,5-(meta) > 2,4-(meta) > 2,5- (para) > 3,4 (ortho). The higher response of the 3,5-polymer may be attributed to the symmetric substitution on the benzene ring, permitting the main chain conformation with less flexibility, as well as a higher Tg.