Responsive Boron Beta-Diketonate Materials

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

Professor Cassandra L. Fraser of the University of Virginia is supported by the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry to investigate the luminescent (light emitting) properties of materials based on difluoroboron beta-diketonates, a family of organic responsive dyes. The many different ways by which these dyes respond to changes in their environment in solution, organized media and the solid state are being investigated. These responsive dye materials change color when scratched, crushed or smeared, and can self-erase with time. As such, they can find use as sensors, optical memory materials, security inks, intelligence contexts, pigments for art and other products. Students from diverse backgrounds obtain multifaceted training in a multidisciplinary environment, engage with a network of local, national and international collaborators and learn science communication skills. Outreach towards K-12 schools is established through ties to a local high school science teacher. An interdisciplinary "Real World Chemistry Lab" is under development to engage students, faculty and the community in chemistry and materials related issues relevant to society. The objective of this proposal is to explore responsive properties of difluoroboron beta-diketonate and bdk dyes in different environments and to consider ways to harness these properties for applications. Informed by computation, this is accomplished by preparing material sets designed to modulate luminescence properties in solution, nanoscale lipid assemblies and molecular solids. Dyes with donor-acceptor substituents, molecular rotors, lipids and other organizing groups are synthesized. Optical properties (emission, lifetime, quantum yield, ultrafast photoluminescence decay) are measured in solution and compared to computed spectra and frontier molecular orbitals. Solvatochromic and viscochromic effects are probed, relevant to investigations with liposomes, membranes and mechanistic probe development. Aggregation induced emission studies characterize the transition from solution to the solid state, whereas dye/polymer blends probe solid-state solvatochromism (dielectric, polar dopants, dye-dye interactions), rigidochromic effects (polymer glass transition temperature, crystallinity), and ML mechanisms, and are readily processable for potential uses. Powder and single crystal XRD provide information about order, dye-dye interactions, and molecular structure, whereas AFM reveals crystallinity and thin film morphologies in molecular solids. Dye assemblies are modeled computationally. Super cooled liquids are investigated by DSC, and mechanochromic properties of dyes are studied for thin films on weigh paper and glass along with new substrates with promising behaviors. A laptop/RGB camera imaging system will characterize dynamic optical effects such as ML recovery, supercooled liquid crystallization, and other luminescence changes in films and assemblies. The expected outcomes of this research are greater fundamental understanding of boron and diketone dye properties in solution, organized lipid media and the solid state. This will lead to more rational design of stimuli responsive, luminescent boron and diketone materials for imaging, sensing and detection applications.