Synthesis and overall nonlinear optical characterization of poly(hexa-2,4-diynylen-1,6-dioxydibenzoate) containing 2,2′-(4-((4-nitrophenyl)ethynyl)phenylazanediyl)diethanol

A new polymer, poly(p-propargyloxybenzoate) containing a polar tolan as nonlinear optically active chromophore was synthesized and characterized. This polymer shows a Tg-value of ∼98 °C and is soluble in typical organic solvents. These properties allowed us to fabricate mechanically stable and high quality semi-transparent thin films by spin coating of N-methylpirrolidone based solutions; obtained samples were adequate for linear and nonlinear photophysical characterizations. In order to explore the quadratic nonlinear optical (NLO) properties, molecular chromophore ordering was electrically induced within the polymeric films via the corona poling method. According to the Maker fringes technique, oriented films with an order parameter of ∼0.25 were able to display large and stable off-resonant second-order NLO-effects such as second harmonic generation (SHG, @ 532 nm); the estimated image and image macroscopic NLO-coefficients were in the order of 186.8 and 71.2 pm V−1, respectively. On the other hand, the cubic NLO-properties of these films were also studied via the Z-Scan technique, where the deposited films displayed an outstanding NLO refractive (n2) and absorptive (β) performance. Indeed, due to the high conjugation degree and intra-molecular charge transfer (ICT) properties, poled and unpoled polymer films displayed huge n2-values in the order of 10−8 m2 W−1 with negative sign and NLO saturable absorption β-coefficients in the order of 10−1 m W−1. The large quadratic and cubic NLO-coefficients obtained for this novel polymer evidence its potentiality in the development of organic-based opto-electronic and photonic prototypes.