Periodic Reporting for period 1 - HELIMIDE ([n]Helicene Diimides: A Twist in Diimide Chemistry)
Reporting period: 2022-08-01 to 2025-01-31
The introduction of chirality in conjugated organic compounds gives rise to properties such as absorption and emission of circularly polarized light, spin-selective charge-transport, and magneto-chiral anisotropy, which enable conceptualization of new functions. Therefore, chiral organic semiconductors (OSCs), which utilize both charge and spin of the carriers, are needed as new materials to drive the development of next-generation (opto)electronics such as spin-LEDs, 3D displays, and quantum-based optical computing. While the field of OSCs has matured, there is an urgent need for chiral OSCs, which can offer high charge-carrier mobilities along with the strong chiroptical response to transform the laboratory-based proof-of-concept research on chiral OSCs into real-world applications. The objective of the proposed research is to develop chiral OSC materials, which will exhibit (i) effective chiroptical responses, (ii) high fluorescence quantum yields, and (iii) dynamic spin-selective charge-transport. To achieve this goal, I plan to develop a new class of functional chiral molecules, namely, [n]helicene diimides ([n]HDI), where two six-membered imide moieties are spanned by an [n]helicene spacer. The proposed research bridges two well-established research fields: (i) planar polycyclic aromatic hydrocarbons bearing diimide units, which are excellent semiconductors, and (ii) 3D [n]helicenes, which display strong chiroptical responses. The research plan will capitalize on three synthetic strategies: (1) A small-molecule approach to gain a fundamental understanding of the structure-function relationship, originating from the through-bond and through-space coupling between imide moieties. (2) A multihelicene approach to expand the application scope by taking control over the electronic energy levels and self-assembly behavior. (3) Macromolecular approach to develop homochiral multifunctional materials employing enantiopure [n]HDIs as molecular synthons.
A novel and efficient synthetic route has been developed for the synthesis of [n]helicene diimides (HDI). This method allows for the key synthetic step—photocyclodehydrogenation—to be performed on a large scale, enabling the availability of target molecules in substantial quantities. Additionally, we have successfully resolved the enantiomers in the desired amounts. This synthesis approach also allows us to precisely engineer the crystal packing of three-dimensional structures, which is crucial for creating efficient charge-transporting materials.
Furthermore, for projects focused on π-extended multi-helicene molecules and supramolecular structures, we have synthesized the key precursor molecules. Over the past two years, we have overcome most of the synthetic challenges, positioning us to advance these projects effectively.
The key precursor for the synthesis of π-extended three-dimensional HDI nanostructures is synthesized. The synthesized precursor molecule exhibited intriguing optical properties: Fluorescence (FL) and circularly polarised luminescence (CPL) over nearly the entire visible spectrum dependent on solvent polarity. Unusual solvent polarity dependence of FL quantum yield and nonradiative rate constant, as well as remarkable gabs and glum values along with high configurational stability. This molecule is published in Chem. Commun. 2023, 59, 14005–14008.
Furthermore, for projects focused on π-extended multi-helicene molecules and supramolecular structures, we have synthesized the key precursor molecules. Over the past two years, we have overcome most of the synthetic challenges, positioning us to advance these projects effectively.
The key precursor for the synthesis of π-extended three-dimensional HDI nanostructures is synthesized. The synthesized precursor molecule exhibited intriguing optical properties: Fluorescence (FL) and circularly polarised luminescence (CPL) over nearly the entire visible spectrum dependent on solvent polarity. Unusual solvent polarity dependence of FL quantum yield and nonradiative rate constant, as well as remarkable gabs and glum values along with high configurational stability. This molecule is published in Chem. Commun. 2023, 59, 14005–14008.
To investigate the molecular spring effect, we synthesized [8]HDI molecules with various bridging units. For the first time, we have elucidated how variations in the helical pitch influence the chiroptical and electrochemical properties of these molecules. These findings provide critical insights into the relationship between molecular structure and functional behavior. We are in the process of drafting a manuscript that details the outcomes of this project, highlighting the novel insights gained through our research.
Through our crystal engineering approach, we have achieved well-defined packing of the three-dimensional structures, which is critical for optimizing the performance of semiconducting materials. This precise molecular arrangement is expected to enhance charge transport efficiency.
Although our initial attempts to construct organic field-effect transistors with high mobility were unsuccessful due to the high LUMO energy levels of the molecules, we are actively addressing this challenge. Our current strategy involves functionalizing the HDI molecules with chlorine atoms to lower the LUMO energy.
Through our crystal engineering approach, we have achieved well-defined packing of the three-dimensional structures, which is critical for optimizing the performance of semiconducting materials. This precise molecular arrangement is expected to enhance charge transport efficiency.
Although our initial attempts to construct organic field-effect transistors with high mobility were unsuccessful due to the high LUMO energy levels of the molecules, we are actively addressing this challenge. Our current strategy involves functionalizing the HDI molecules with chlorine atoms to lower the LUMO energy.