External Stimuli Driven Transformation of BN-Heterocycles
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Authors
Yang, Dengtao
Date
Type
thesis
Language
eng
Keyword
Photochemistry , Boron Chemistry , BN-Heterocycles , Hydroboration , Luminescent Materials , Photoresponsive
Alternative Title
Abstract
BN-heterocycles have important applications in synthetic methodologies, chemical reactivity and optoelectronics. This thesis focuses on the investigation of the thermal and photo-responsive properties of BN-heterocycles as well as applications in optoelectronic devices. In search of more efficient photoelimination of BN-heterocycles, we found that BN-heterocycles could have different and unique transformations upon external stimuli. The preparation of the BN-polycyclic aromatic hydrocarbons (PAHs) is also described.
Boranes with the general formula of HBR2 have been found to undergo a facile 1,1-hydroboration reaction with pyrido[1,2-a]isoindole, resulting in insertion of a BR2 unit into a C-N bond and the formation of a variety of BN-heterocycles. Investigation on the thermal reactivity of the BN-heterocycles revealed that these molecules have two distinct and competitive thermal elimination pathways: HBR2 elimination (or retro-hydroboration) versus R-H elimination, depending on the R group on the B atom and the chelate backbone.
Given the 1,3-dipolar nature pyrido[1,2-a]isoindole, a “one-pot” cycloaddition procedure of pyrido[1,2-a]isoindole and its analogues with dimesitylboron functionalized alkynes has been successfully developed for the synthesis of a series of BMes2-functionalized N-heterocycles.
To further expand the photoelimination reaction to multiple BN-doped PAHs, new BN-heterocyclic compounds have been found to undergo double photoelimination, forming rare yellow fluorescent (BN)2-arenes that contain two B-N units. Most significant is the discovery that the double elimination can also be driven by excitons generated electrically within electroluminescent (EL) devices, enabling the in situ solid-state conversion of BN-heterocycles to BN-arenes and the use of BN-arenes as emitters for EL devices. The in situ exciton-driven elimination (EDE) phenomenon has also been observed for other BN-heterocycles.
Besides changing external stimuli to improve the efficiency of elimination of BN-heterocycles, the internal factor - the effect of substituents on boron atom was also investigated. We found that both electronic and steric effects have a significant and distinct impact on the photoreaction pathways of BN-heterocycles. With bulky, electron-donating aryl rings on the B atom, the photoelimination efficiency is enhanced. In contrast, with sufficiently electron-withdrawing aryl groups on the B atom, bulky or not, photoisomerization occurs exclusively with a high stereoselectivity.
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Queen's University's Thesis/Dissertation Non-Exclusive License for Deposit to QSpace and Library and Archives Canada
ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Queen's University's Thesis/Dissertation Non-Exclusive License for Deposit to QSpace and Library and Archives Canada
ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.