Sterically hindered pyridinium phenoxides as chromophores for quadratic optics

摘要

Polymers doped with non-linear optical (NLO) molecules are key materials in the elaboration of organic NLO devices. In this field, there is an ongoing need for chromophores with large dipole moments and optical non linearities. Here, we consider pyridinium phenoxides, a type of zwitterionic biphenyl-like molecule. A combination of mathematical modelling and some preliminary experimental measurements indicate that the NLO properties of these molecules depend on the twist angle existing between the two aromatic rings. In order to corroborate this structure/activity relationship, different sterically hindered pyridinium phenoxides were synthesized using the Suzuki coupling reaction involving a boronic ester and an aryl halide. We analyze the solvatochromism of the substituted zwitterions in details, determine the chemical equilibrium of protonation and perfom nonlinear optical measurements which are interpreted with the help of semi-empirical calculations.