Fluxional Aromatics: Dynamic Electronic Behavior of Aromatic Compounds leads to Unique Material Properties

Photochromic;diradical;organic electronics;Chemistry

DeFrancisco, Justin

Johns Hopkins University

关键词: Photochromic;    diradical;    organic electronics;    Chemistry;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/60112/DEFRANCISCO-DISSERTATION-2018.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Aromaticity as a phenomenon which stabilizes a certain class of hydrocarbons hasbeen studied for centuries. This view of aromaticity as a static force which a compoundeither does or does not experience continues to prevail in introductory chemistry courses.More recent research has revealed that aromaticity can be much more dynamic than oncethought. This sort of dynamic aromaticity can lead to unique electronic properties, thatmay be useful in organic electronic materials. This work focuses on two branches ofmaterials, photochromic compounds and diradicals, which might make use of dynamic orfluxional aromaticity.First, aromatic photochromic compounds, which change properties when exposedto light, are investigated. These compounds hold promise for acting as conductivityswitches in conductive polymers. Promising diarylethene targets with aromatic cores arefirst modeled through quantum chemical calculations, then synthetic attempts are detailed.Spectroscopic evidence of photochromism is documented for successfully synthesizedswitches.Next, the electronic properties of quinoidal oligomeric compounds are examined.These proaromatic compounds can regain aromaticity by adopting an open shellelectronic configuration. This equilibrium between closed shell quinoidal and open shellaromatic configurations can be influenced by a number of factors. First, various quinoidaloligomers containing the classic aromatic hydrocarbon 1,6-methano[10]annulene areinvestigated. The influence exerted by sterics on these TMTQ derivatives are studied.Using electronic, magnetic, and vibrational spectroscopies, magnetic measurements, andquantum chemical calculations, different steric effects on an identical π conjugatediibackbone is shown to greatly influence the diradical character of a system. The possibleextent of this steric effect is explored through quantum chemical calculations and newsyntheses. The effect of the identity of the other proaromatic rings in the quinoidaloligomer with M10A is also explored.Proaromatic quinoidal oligomers featuring the same alternating pattern in TMTQbut without M10A are explored next. The planar molecular geometries predicted inquantum chemical calculations give rise to properties that were not seen in the TMTQderivatives. Synthetic attempts to these compounds are also documented. Finally,derivatives of benzoquinodimethanes are investigated through computational predictions,to try to gain insight into the relative preference for singlet or triplet diradicals in thesesystems.