The proposed research is a continuation of the current NSF award and involves the design, synthesis, and study of liquid crystalline materials that are uniquely suited to address fundamental questions and applied problems in the field of liquid crystals. The proposed materials are nematic liquid crystals containing boron clusters, a class of compounds that displays unusual steric and electronic properties. Because these materials have the potential to meet technological needs in modern society, the project has two related goals: the development of new materials for applications in flat panel displays and new liquid crystalline electrolytes for rechargeable Li+ ion batteries. The project involves the molecular design of new materials aided by quantum-mechanical calculations, inorganic/organic synthetic methods, structure-property relationship studies, electrooptical characterization and ion mobility investigations.
NON-TECHNICAL SUMMARY:
This multidisciplinary program is directed at the development of new advanced molecular materials for addressing fundamental questions in the field of liquid crystals and for applications in flat panel displays and rechargeable batteries. The design involves unique organic-inorganic hybrid molecules, which will be synthesized and investigated using a broad array of modern research tools. The proposed work will affect a number of areas of science and engineering, and is expected to impact LCD and energy storage technologies. It will provide excellent opportunities for the involved personnel (undergraduate and graduate students and also postdoctoral workers) to obtain broad training in modern materials chemistry through domestic and international collaborations, which include the LCD industry (e.g. Vision in Colorado).
Boron clusters (shown in Figure 1) are unusual inorganic cage compounds that we have been exploring as structural elements in rod-like liquid crystals (partially organized fluids). Their atypical geometry and electronic structures (electron delocalization, polarizability, and the overall charge) permit the design of unusual functional materials suitable for flat panel display and solid-state battery applications, as well as for the study of fundamental aspects of the liquid crystal phenomenon. Our multidisciplinary research program is directed at synthesis and understanding of behavior of rationally designed liquid crystalline materials derived from such clusters. The project involves a broad spectrum of activities that include molecular design (aided with quantum-mechanical calculations), synthetic methods (both organic and inorganic), structure-property relationship studies, and electrooptical characterization, and is concentrated in five main areas: i) fundamental chemistry of the [closo-1-CB9H10]- (6) [closo-1-CB11H12]- (1) and [closo-B10H10]2- (5) clusters (Figure 1) ii) investigation of highly polar liquid crystals derived from the [closo-1-CB9H10]- (6) [closo-1-CB11H12]- (1) clusters iii) development of anion-driven ionic liquid crystals derived from the [closo-1-CB9H10]- (6) [closo-1-CB11H12]- (1) clusters iv) structure-property relationship studies and electrooptical characterization of carborane derivatives v) modification of properties of nematic and FLC materials by carborane additives. Some major accomplishments are summarized below. Scientific outcomes 1. We have optimized and scaled up the synthesis of iodo acid 8 (CHART I) and use it to prepare carboxylic acid [closo-1-CB9H8-1-COOH-10-N2] (9), in which we investigated transformations of the N2 group at the B(10) position. As a result, we have developed synthetic access to key intermediates 8 and 9, and also methods for functional group transformations indispensible for the preparation of liquid crystals containing the [closo-1-CB9H10]- cluster. 2. Armed with the newly developed synthetic methods, we prepared a series of zwitterions 10[n] with the dipole moment μ ~15 D, and investigated them as low concentration high Δε additives to nematic materials. Such compounds are of interest to improve electrooptical performance of the LCD. 3. To improve properties of zwitterionic derivatives of [closo-1-CB9H10]- and their compatibility with the nematic hosts, we have developed two series of esters 11[n] and 12, both derived from acid 9. Most of these esters form nematic phases above 100 oC. Dielectric studies demonstrated that 12d, (Cr 128 (N 129) I; μ= 20 D), exhibits a record high dielectric anisotropy in nematic solutions (Δε =113.5!). This and other compounds 11[n] and 12 are subject to patent protection as polar additive to nematic mixtures with improved electrooptical characteristics. 4. Using zwitterionic liquid crystals 12 and their isosteric non-zwitterionic analogues 13, we addressed for the first time one of the fundamental questions in liquid crystal research: how much can an electric dipole stabilize a nematic phase? The exchange of the C–C fragment in carborane derivatives 13 for the isosteric polar fragment N+–B- in zwitterions 12 increases the longitudinal dipole by 12 D (CHART I). This is a significant result providing a unique experimental test for many theoretical considerations of the effect of molecular structure on phase behavior that appeared during the past several decades. 5. In parallel with highly polar liquid crystals, we have developed access to a new class of ionic liquid crystals in which the anion has the elongated shape and drives the liquid crystalline behavior. Thus, form the iodo acid 8 we prepared two series of liquid crystalline ion pairs 14a and 14b. Behavior of some of esters 14a has been compared to those of the analogous esters 15 derived from the [closo-1-CB11H12]- cluster. Further optimization of their molecular structures should result in ion pairs containing the Li+ cation and useful for anisotropic electrolytes for solid-state batteries. 6. A new class of liquid crystalline bis-betains 16 derived from the [closo-B10H10]2- (5) cluster with interesting photophyscial properties has been discovered and investigated. Broader Impact This NSF-sponsored project has offered a balanced and modern combination of experiment and theory augmented by the aesthetic appeal of liquid crystals. The combination of synthetic chemistry and fascinating properties of liquid crystals are particularly attractive to undergraduate students, who were recruited mainly from my organic chemistry classes. The participating coworkers developed broad skills in boron cluster chemistry and characterization of liquid crystals. Thus, the project has offered research training to a total of 7 undergraduate , 2 graduate students, and 1 postdoctoral associate. The results were disseminated in the form of presentations at local, national, and international scientific meetings, 13 publications in refereed journals, a book chapter, a patent application, and one invention disclosure. Presentations demonstrating fascinating properties of liquid crystals and their role in modern technology have been incorporated to Organic Chemistry and graduate level classes. We also work the Adventure Science Center in Nashville. In 2011, we gave an hour-long presentation to young audience on liquid crystals as part of NSF-sponsored Making Stuff series. The presentation included hands on activities and take-home kits.
