Rigid-Rod-Like Main Chain Polymers with Rigidly Attached Chromophores. A Novel Structural Concept for Electrooptical Materials. 1. Synthesis and Characterization

Abstract

A structural concept for nonlinear optical (NLO) polymeric materials optimized for long-term stability of the polar order is presented: rigid-rod-like main chain polymers furnished with long alkyl side chains with a portion of the side chains being replaced by NLO-active chromophores were synthesized. The chromophores are rigidly attached to the main chains, normal to the direction of the polymer backbone. In this particular geometry the motion of the NLO-active chromophores is restricted to a two-dimensional rotation around the stiff main chain. X-ray diffraction experiments on spin-cast films of the polymers show a lamellar structure with a preferential orientation of the layers parallel to the substrate plane. The incompatibility of polar main chains and nonpolar side chains leads to this microphase segregation. This layered structure improves the long term stability of polar order in the poled polymer film. Dielectric spectroscopy revealed only one relaxation process of large dielectric strength. The Arrhenius-type temperature dependence of relaxation times indicates a locally activated motion of the chromophores.

Second-order non-linear optical polymers

“…For example, Köhler et al 12,13) compared relaxation dynamics of side-chain and main-chain NLO polymers. Heldmann et al 14,15) and Firestone et al 16) studied relaxation of poled order in rigid-like polymers with chromophores rigidly attached to the main-chain. Kaatz et al 17) , Winkelhahn et al 18) and Burland et al 10) have correlated orientational behavior above and below T g quantitatively using established theories for relaxation in glass forming materials.…”

Transport and Electro‐Optical Properties in Polymeric Self‐Assembled Systems

“…Importantly, the poled chromophores are prone to relaxation towards the thermodynamic nonpolar equilibrium state, which can be a serious limitation considering the applications. In an effort to control the relaxation of the chromophore alignment, they have been covalently bonded to rigid rod polymers that undergo lamellar self-assembly [410][411][412][413]. Given that the system is poled before the self-assembly is frozen, the relaxation can be effectively suppressed to be only two-dimensional within the self-assembled lamellar layers.…”

Investigation of dipole alignments by swelling in poled thin films of a side-group polymer using second harmonic generation

“…In the case of this rigid polymer system, film preparation by spin coating leads to the planar orientation of backbone chains by flow-induced planar stacking of rigid segments, 4,10,11 and side groups are tilted with respect to the main-chain layers to decrease the distance between neighboring side groups. 12 It is also plausible that methanol molecules tend to solvate the chromophore selectively. We confirmed this from the reproducibility of the data.…”