Chiral chromophore-functionalized polybinaphtalenes for second-order nonlinear optics

Abstract

Here we report on the second-order nonlinear optical properties of chiral chromophore-functionalized polybinaphtalenes. These materials are designed from chiral binaphtalene units, connected with rigid groups. This molecular architecture gives rise to a rigid, rod like (helical) structure. Chromophores which moderate to good hyperpolarizabilities were incorporated to induce a strong second-order nonlinear optical response. The polymers are soluble in common organic solvents and spincoated films of high optical quality can be readily obtained. The spincoated films were subsequently poled by an external electric field and analyzed by second-harmonic generation. The films showed excellent second-order nonlinearities, as high as 100 pm/V. Maybe even more important was the observation that the nonlinearity of these materials increases linearly with increasing chromophore content, in contrast to what has been observed for traditional side-chain polymers. This is due to the rigid character of the polymer backbone which effectively prevents detrimental chromophore aggregation at high chromophore concentrations. This property opens up perspectives to achieve materials with very high second-order nonlinearities. Another interesting observation was the fact that chiral contributions to the nonlinear optical response can be observed, which may further increase the nonlinearity.