Helically Twisted Functional Chiral Nanostructures

• Applicant: Dr. Princekumar Ravat
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448604676

Helically twisted π-conjugated molecules, in particular helicenes and twistacenes, represent a unique class of polycyclic aromatic hydrocarbons (PAHs) to investigate various phenomena arising from the interplay of their inherent axial chirality and unique optoelectronic properties. From the standpoint of potential applications, the properties that emerge in chiral helicenes and twistacenes, such as circular dichroism and circularly polarized luminescence, are of interest for future display technologies, photonics, and bio-responsive imaging. Both classes of molecules are very well explored and numerous synthetic methodologies and structural modifications have been investigated for several applications. However, in order to translate these proof-of-principle concepts to real world applications and, more importantly, to expand the fundamental understanding of the physical chemistry of these molecular-systems when their structures are extended into nanometer-sized domains, following challenges remain: (i) Modulating the HOMO–LUMO energy gap of helicenes while preserving their chiroptical properties. (ii) Isolation of twistacenes in enantiomerically pure form with sufficient stability under ambient conditions. (iii) Systematic investigation of the effect of π-extension in helicenes/twistacenes with different geometries on their (chir)optical responses. (iv) Control of the conformation of helically twisted molecular wires and ribbons.To address above mentioned challenges, my research plan is focused on: (1) bottom-up stereospecific synthesis of nanometer-sized, structurally well-defined helically twisted chiral functional molecules, namely, (i) nanowires and (ii) nanoribbons. Based on preliminary DFT calculations I envisage employing [n]helicenes as a molecular wrench to control the conformation and stereodynamics of helically twisted wires and ribbons. (2) The systematic investigation of synthesized molecules using in-depth steady state and time-resolved spectroscopy, supported by DFT calculations, will be performed in order to obtain an insight into their structure-property relationship and to analyze the effects that may arise from the marriage of chirality and optoelectronic properties, for example, how HOMO–LUMO energy gap, optical rotation, circular dichroism and circularly polarized luminescence properties are changed or tuned by extending π-conjugation and helicity in different dimensions and symmetries. (3) Exploring the potential of these nano-structures for applications in organic electronics and investigating physical phenomena, namely, Chirality Induced Spin Selectivity and Magneto-Chiral Anisotropy.

• DFG Programme: Research Grants