UNB Scholar Research Repository :: Browsing by Author "Eisler, Sara"

Browsing by Author "Eisler, Sara"

Now showing 1 - 9 of 9

Approaches toward white light emission and programmable fluorescence, along with the serendipitous discovery of a series of pericyclic cascade reactions
(University of New Brunswick, 2023-06) Price, Jayden T.D.; Eisler, Sara
Research in molecular fluorescence has led to more energy-efficient LED displays, single-molecule level detection limits in microscopy, and increasingly complex anti-counterfeiting measures. However, synthetic and design challenges associated with the realization of white, red, and blue light-emitting systems with the properties required for commercialization still exist. First, we explore the use of multicomponent photoluminescent systems, containing a mixture of simultaneously emitting organic molecules to access white light and programmable emission color. By mitigating the potential for energy transfer through the control of concentration, we show that the emission color is approximated as a linear combination of the emitting components and their corresponding brightness. Based on these results, we demonstrate that the ratio of red, green, and blue emitters needed to achieve hard-to-reach WLE can be predictably determined. Second, we show that one molecular scaffold, thioarylmaleimide (TAM), can be used to access blue to deep-red emission colors with high quantum yields in just one synthetic step. A series of mono and bis-substituted TAMs are synthesized from commercially available starting material in moderate to excellent yields via Suzuki-Miyaura (SM) cross-coupling. Photophysical properties, including wavelength and quantum yield, are controlled by adjusting the conjugation, connectivity, and the number of thioaryl groups attached to the maleimide. A marked decrease in the SM coupling yield of monosubstituted TAMs prompted the serendipitous discovery of a series of pericyclic cascade reactions leading to crowded thienyl and benzo[b]thienyl fused architectures. Stereochemical assignment is achieved using a combination of NMR studies, chemical shift calculations and DP4+ analysis. Transition-state calculations support an asynchronous concerted mechanism and provide support to rationalize the regio- and diastereoselectivity that is observed.
Controlling regioselectivity of cyclization in heterocyclic alkynylamides
(University of New Brunswick, 2021-12) Infante, Genesis; Eisler, Sara
Competitive 5-exo/6-endo anionic intramolecular cyclization reactions in heterocyclic alkynylamides were explored via experimental and computational analysis. The 5-exo-dig cyclization pathway is usually disfavoured in heterocyclic systems, and 6-endo products are often both the kinetic and thermodynamic products. However, it was discovered that it is possible to shift selectivity toward the 5-exo-dig pyrrolone products and away from the less strained pyridinone products that are produced via the 6-endo-dig cyclization. Parameters such as identity of heteroatom, heteroatom positioning within the heterocycle, and functionality on the alkyne were investigated and in many cases were found to strongly influence product ratios. A series of computational studies was performed to provide further insight into the 5-exo and 6-endo-dig pathways in these heterocyclic systems. Theoretical predictions were found to reproduce experimental results, highlighting the predictive capabilities of the computations in determining preferred products. The established experimental and predictive computational protocols were then applied to more complex bisalkynylamides. The subsequent competing tandem cyclization pathways, 5-exo/6-exo-dig and 5-exo/7-endo-dig, were predicted and controlled using established experimental and theoretical concepts from earlier studies.
One-pot synthesis of tetrasubstituted isoindolinones
(University of New Brunswick, 2017) Almansour, Milhah; Eisler, Sara
The isoindolinone functionality and its derivatives are present in many naturally occurring and biologically active compounds. Tetrasubstituted isoindolinones such as 3, while a useful building block in materials as well as natural product synthesis, are particularly challenging to make. Current methods to make tetrasubstituted derivatives often require harsh conditions and expensive catalysts. Therefore, we decided to investigate a one-pot synthesis of this functional group using 5-exo-dig cyclization. Our strategy involved the intramolecular cyclization of alkynylbenzamide 1 using anhydrous conditions and trapping intermediate 2 with an electrophile. Several variables were investigated such as solvent, time, temperature, and identity of electrophile. Although the reactivity of intermediate 2 limited our choice with respect to solvents and electrophiles, we were successfully able to obtain target product 3 under certain conditions. Optimization and scope of the reaction will be discussed.
Synthesis and electronic properties of dibenzothieno-isoindole dione building blocks for organic electronic devices
(University of New Brunswick, 2017) Albright, Emily; Eisler, Sara
The ability to control the physical and electronic properties of conjugated polymers and small molecules has led to considerable focus on developing new electron-accepting (EA) and electron-donating (ED) building blocks, which are essential for obtaining new and efficient organic electronic materials. This work involves the design, synthesis and characterization of fused thieno-isoindole scaffolds as versatile electronic building blocks. The advantages of the dibenzothieno-isoindole dione scaffold include the potential for a concise, 3-step synthetic route from easily available starting materials and the capacity to fine-tune physical, optical, and electronic properties via numerous synthetic handles. A short efficient synthesis to dibenzothieno-isoindole dione derivatives was therefore developed from commercially available starting materials. Two steps are required; a Suzuki-Miyaura coupling followed by an oxidative cyclization. The synthesis of several dibenzothieno-isoindole dione derivatives will be discussed as well as structure activity relationships, solid-state structure, and physicochemical properties. The investigation of noncovalent interactions involving halogens has led to the discovery of numerous reliable motifs for supramolecular design. Four isomers of diiodo-xylene were synthesized and their single crystal X-ray structures determined. I⋯I interactions were found to play a strong role in defining the crystal packing patterns of these simple aromatic structures.
Synthesis of novel boron-coordinated fluorophores and the synthesis toward an ene-imine 1H-isoindole oligomer
(University of New Brunswick, 2021) Dean, Ryan; Eisler, Sara
Nitrogen containing heterocycles are widely incorporated into small, conjugated molecules and extended π-systems that possess desirable properties for use in organic electronics (OE) and fluorescent dyes. Of particular interest is the ene-imine moiety, which is a critical component in porphyrin and boron-dipyrromethene (BODIPY) chromophores. BODIPYs are known for their intense fluorescence, small Stokes shifts, narrow optical bands, and large quantum yields. Despite the importance of the ene-imine motif, it is rarely observed outside of the aforementioned systems due to synthetic inaccessibility. Recent work has led to the synthesis of a new class of ene-imine bearing BODIPY-like fluorophores, the lactam BODAZAs (Boron-DiAZA-methene). Lactam BODAZAs possess large Stokes shifts, broad optical bands, and retain fluorescence in the solid state, all of which are rare feats for BODIPYs. This thesis details the expansion of the lactam BODAZA series using a generalized synthetic methodology and has resulted in the synthesis of two new lactam BODAZA fluorophores and the investigation of their optical properties. Recent advances in the development of ene-imine molecular building blocks have allowed for an investigation into the linear extension of the moiety via oligomerization. By tethering 1H-isoindole building blocks together, a linear conjugation pathway of ene-imine fragments can be produced and facilitate an investigation into the effect of conjugation length on the optical and electronic properties of the moiety. The synthesis toward an extended ene-imine conjugated system is detailed in this thesis.
Synthesis of organic building blocks featuring the ene-imine motif
(University of New Brunswick, 2018) Fillmore, Brandon; Eisler, Sara
Nitrogen-containing heterocycles, or building blocks, have been shown to possess outstanding properties, in small molecules and polymers, for applications in organic solar cells (OSCs), organic light-emitting diodes (OLEDs), and organic thin-film transistors (OTFTs). To further advance our understanding of structure-activity relationships in organic semiconductors, and to improve their performance, new organic building blocks that can be fine-tuned to have desired properties are required. The ene-imine conjugation pathway is of interest for various reasons. For example, boron-dipyrromethenes (BODIPYS) are planar, π-conjugated small molecules that can be tuned to absorb light in the red to near-infrared region, which is beneficial for applications such as organic electronics and bioimaging. However, available synthetic strategies toward BODIPY systems limits the scope of derivatives that can be achieved. Several ene-imine derivatives were prepared according to the developed synthetic procedure described herein in yields of 23-52% over two steps. The optical properties were determined by UV-vis, and the solid-state packing properties by X-ray crystallography.
The design, synthesis, and properties of isoindolinone molecular switches
(University of New Brunswick, 2018) Cameron, David; Eisler, Sara
The design, synthesis and photophysical analysis of bi- and multi- stable photoswitches based on the isoindolinone heterocycle was carried out. The design process included a rational computationally assisted modelling approach that used density functional theory and time dependent density functional theory to perform a geometry optimization on a structure of interest and predict its optical absorbance properties. If the target molecule exhibited a large separation of its absorbance profile in one isomeric form over the other, it became a synthetic target. The synthesis of three photoswitching targets was attempted but not completed. The progress towards the synthesis of two of the targets was significant, while the other was abandoned at an earlier stage. The thiophene substituted and benzothiophene substituted aryl ester intermediates from the synthetic pathway towards the isoindolinone photoswitches were discovered to have unique optical properties in solution, films and the solid state. For these reasons, the photophysical properties of the thiophene and benzothiophene substituted aryl esters were studied.
The Synthesis and Electronic Properties of Responsive, [pi]-Conjugated lsoindolinone Small Molecules
(University of New Brunswick, 2012) Estey, Paula; Eisler, Sara
Isoindolinone ring systems are found in a variety of natural products and synthetic pharmaceuticals, but also possess interesting electronic properties that can be used in organic electronics. Incorporation of isoindolinone units into oligomer targets with extended conjugation for applications such as organic photovoltaics (OPV) and organic field-effect transistors (OFETs) requires a versatile and facile synthetic method. We have developed a nucleophilic fluoride-induced cyclization between an amide and a neighbouring substituted alkyne to form an isoindolinone, which allows facile variation of the conjugation length and overall molecular structure, providing the opportunity to develop many isoindolinone derivatives with extended [pi]-conjugation. We have synthesized a variety of isoindolinone-containing compounds that exhibit responsiveness to both acid and UV light by isomerization between the E and Z form at the alkene. Preliminary switching studies using two promising targets have been completed toward the development of multi-stable switches.
Thioarylmaleimides: accessible, tunable, and strongly emissive building blocks
(Royal Society of Chemistry, 2019) Price, Jayden; Albright, Emily; Decken, Andreas; Eisler, Sara
A series of thioarylmaleimides was synthesized to investigate how variation of the thioaryl group can be used to control absorption and emission properties in solution and in the solid-state. Fine-tuning of the photochemical properties was found to be possible using this strategy, and a rainbow of colours and emission wavelengths are accessible in a single step from commercially available compounds.

Browsing by Author "Eisler, Sara"

Results Per Page

Sort Options