Engineering Electronic Diversity and Synthetic Versatility into Borepin-based Pi-conjugated Organoboron Materials

boron;borepin;organoboron;organic materials;polycyclic aromatics;pi-electron materials;pi-conjugated materials;functionalization;electronic structure;isomerism;redox chemistry;fluoride-binding;Chemistry

Levine, David RobertTovar, John D. ;

Johns Hopkins University

关键词: boron;    borepin;    organoboron;    organic materials;    polycyclic aromatics;    pi-electron materials;    pi-conjugated materials;    functionalization;    electronic structure;    isomerism;    redox chemistry;    fluoride-binding;    Chemistry;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/39731/LEVINE-DISSERTATION-2016.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Embedding tricoordinate boron atoms within carbon-based π-conjugated networks has emerged as a powerful strategy for property-tuning owing to the characteristic electron-deficient properties associated with the vacant pz-orbital of boron.The borepin ring – a formally Hückel-aromatic 6π-electron heterocycle – has recently begun to be reinvestigated as a promising architectural motif to install boron functionality into extended, synthetically modifiable ladder-type polycyclic π-electron systems.However, a thorough elucidation of structure-property relationships in borepin-based materials and the development of robust synthetic methods to access a wider variety of such materials is an area requiring further work.This dissertation presents the synthesis, characterization, and further functionalization of novel polycyclic aromatics featuring benzo- and thieno-fused borepin rings. To orient the reader, Chapter 1 features a brief introduction to the field of boron-containing polycyclic aromatic materials.Chapter 2 describes the synthesis of parent and functionalized analogues of the ;;meta-B-entacene” scaffold, a pentacyclic ladder-type structure containing two fused borepin rings.The work provides insight into the electronic impact of positing two boron atoms within a rigid, polycyclic array in a meta-arrangement, leading to narrowed optical bandgaps and more difficult electrochemical reductions than for the isomeric para-B-entacene.Chapter 3 describes the synthesis and characterization of a series of isomeric dithieno[b,f]borepins (DTBs), wherein the flanking thiophene rings are fused to the central borepin in different orientations.These studies feature a new, scalable synthetic approach to construct borepin rings, relying on direct condensation of dimetalated intermediates with a mesityl boronic ester instead of traditional tin-boron exchange chemistry. Theoretical, structural, electronic, and redox analyses demonstrated DTBs possess several desirable properties of typical π-conjugated organoboranes and that the conjugation pattern of each isomer influenced molecular properties.Chapter 4 details the investigation of the chemical reactivity of DTBs introduced in Chapter 3 and the development of synthetic methods for late-stage functionalization and property-tuning.Cross-coupling of synthetically primed DTBs led to a series of π-extended derivatives with diverse properties (including highly polarizable electronic structures and multi-electron accepting capacity), which could be tuned based upon the electronics of the appended substituent and the conjugation pattern of the DTB backbone.Chapter 5 describes studies of other thiophene-annulated borepins wherein the borepin ring lacks a formally Hückel-aromatic π-electron arrangement.This includes the synthesis and characterization of a stable trithieno[b,d,f]borepin (TTB) and preliminary efforts to access DTBs with a quinoidal π-electron structure.Chapter 6 describes early stage efforts to construct extended ladder-type thiophene-fused borepin arrays featuring thiophene rings. Suggestions for future directions in borepin-based materials research are provided.