A Theoretical and Synthetic Investigation of New Donors for Organic Electro-Optic Chromophores: Understanding the Effects of Structure and Substituents on Donor Strength

Abstract

Understanding of the intricate connection between shape, structure and property has al- lowed many challenges facing the adoption of organic chromophores for electro-optic (EO) applications to be overcome. Still, there is much to be learned about designing donors that localize electron density in the ground state, but not in the electronically polarized state to allow for enhanced charge transfer, and thus, large first-order molecular hyperpolarizability (β). To address this, density functional theory has been used to evaluate a large number of potential donors based on alkyl, aryl, saturated and unsaturated heterocycles. These were coupled to the tricyanopyrroline (TCP) acceptor by a simple vinylic bridge to identify new high β, high number density materials. Saturated heterocylces were found to off the largest improvements over traditional dialkyl donors, with the predicted systems rival- ing much longer polyene-based chromophores with a trifluoromethyl, phenyl-tricyanofuran (CF3PhTCF). Other potential candidates where based on diaryl amines donors which are a natural progression from previous heteroaryl chromophores. These systems were typified by a greater degree of localized electron density – by as much as 20% – at the donor and were found to exhibit characteristics that might described as a double-donor. Several novel chromophores based on these new donors were synthesized to verify the theoretical results and evaluate their potential for use in EO devices.