Projects:
Nonpolar Electro-Optic Materials

Supported by National Science Foundation

Co-PI: Prof. Kenneth Singer
Co-PI: Prof. Rolfe Petschek

Co-PI: Prof. Robert Twieg

ABSTRACT:

An interdisciplinary focused research group will investigate nonpolar chiral media comprised of polar or nonpolar, chiral or achiral molecular constituents for use in electro-optics and second-order nonlinear optics (NLO). Team members in organic synthesis, theory, and NLO measurements will work together closely in order to understand and develop the molecular and supramolecular features necessary for applications in image-plane electro-optic devices. The proposed work is timely, of significant intellectual merit and expands upon our recent theoretical and experimental results that have identified promising molecular features and specific material classes for investigation in this project.

Chiral NLO materials may possess a number of advantages for producing second order NLO materials with properties superior to those of conventional dipolar systems: greater thermal and photo stability, better trade-off between optical nonlinearity and transparency and more favorable phase-matching properties. Chiral materials are necessarily noncentrosymmetric and have second order NLO susceptibilities even when there is no polar order thus reducing problems due to dipolar forces and providing more robust and stable materials. Studies will focus on axially ordered non-polar bulk materials composed of either polar or non-polar multidimensional molecules, and including calamitic and columnar liquid crystalline phases as well as mechanically oriented polymers.

We have identified quantum features that lead to large molecular responses in specific types of materials. In particular, a variety of lambda-shaped molecules have been prepared and shown to optimize the relevant optical nonlinearity on the basis of a two-level model, and the predicted molecular hyperpolarizability figures of merit have been experimentally substantiated. We have developed a novel hyper-Rayleigh scattering experiment along with the theoretical basis that can measure all of the molecular hyperpolarizability figures of merit corresponding to the rotationally invariant tensors of the hyperpolarizability.

We plan to continue and expand this promising research and have formulated the following plans and objectives: (1) Design and synthesize robust nonchiral and chiral two- and three-dimensional conjugated molecules for application in second-order NLO. (2) Develop the theoretical and analytical tools for molecular engineering of these NLO materials. (3) Investigate the use of such molecules in macroscopic chiral systems including mechanically aligned polymers and various calamitic and columnar liquid crystal phases. (4) Investigate electro-optic image plane modulation and device structures leading to GHz bandwidth spatial light modulators.

Materials to be synthesized in this project include: (1) non-cyclic terminated lambda-shaped molecules and chromophores based on Crystal Violet that both possess large merit figure based preliminary measurements, (2) macroheterocyclic ring chromophores, (3) discotic chromophores with macroheterocycle or longitudinally twisted chromophore cores, (4) helical polymers containing these types of chromophores. Characterization methods to be employed include hyper-Rayleigh scattering, coherent second harmonic generation and the linear electro-optic effect, as well as linear optical characterization. Theory will focus on quantum chemistry and molecular and supramolecular conformations and interactions.

Beyond the substantial intellectual merit of the project, broader impact will manifest itself in a variety of ways. The research materials, methods and concepts created here will contribute to a new electro-optic technology for optical data and image processing and also to the knowledge required to promote optoelectronics in general. Our project integrates education and research, and will include participation of two graduate students and one post-doctoral researcher and prepare them for a career in optoelectonics or a related critical workforce area. Undergraduate students involved in the project will be engaged in research that will provide a very tangible and exciting component of their education and motivate them to complete that first phase of their education and to contemplate graduate studies. Overall, the project will enhance development of scientists trained in interdisciplinary efforts in organic chemistry, physics, and optics.