The synthetic development and generation of liquid crystalline radicals.

摘要

This dissertation presents a part of nearly decade-long research project. The main goal of this research is to develop a series of discotic liquid crystals based on electrically neutral, persistent heterocyclic radicals with pi-delocalized spin and study their properties, in the context of the organic molecular magnetism (Figure 1).*.;The strategy of this long-term project comprises four main parts: (a) development of synthetic pathways and stability determination of the parent radicals (R = H); (b) structure-property relationship studies of 1--4 closed-shell analogs to radicals A--D to aid the design of liquid crystalline radicals; (c) preparation of direct precursors to radicals A--D; (d) isolation and characterization of mesogenic radicals in their pure form.;The synthesis of the parent radicals A--D (R = H) relies on the preparation of a series of 2,6-heterodifunctional halobenzenes as precursors to substituted biphenyls with the appropriate functional groups used to close the heterocyclic rings.*.;The study of closed-shell analogs 1--4 (Figure 2) demonstrated that 3,4-dioctyloxyphenyl group induces mesogenic behavior, except for the phenanthrene derivative 3b. The liquid crystalline studies showed that benzo[c]cinnoline (1b), tetraazapyrene (2b), and pyrene (4b) derivatives form mesophases with two-dimensional hexagonal lattice. These mesophases supercool and form glass with the structure of the preceding hexagonal phase.;Also the preparation of polyfunctional biphenyls as key intermediates to potentially discotic radicals A--D was accomplished.;So far, the synthesis of radical A was completed. The ESR signals were consistent with the radical structure. This radical is relatively persistent in the solid state. However, it was difficult to purify chromatographically and showed low stability in solutions.;Additionally, as a part of discotic liquid crystalline studies a series of carbazole derivatives was prepared. Similarly to compounds 1b, 2b, 4b only derivative with 3,4-dioctyloxyphenyl substituent forms hexagonal columnar mesophase. The photoconductive behavior of mesogenic carbazole and pyrene (4b) derivatives was investigated. The studies showed photoconductivity typical for columnar discotic phases about 10-3 cm2/sV.;*Please refer to dissertation for diagrams.