Venkata Suresh Mothika

Key words: Heterohelicenes, non-planar chiral polyaromatic compounds, high-spin organic radicals, spin-polarized organic materials, organic electronics, spintronics.

• Our current research focus is on redox-active non-planar, twisted aromatic systems in particular redox-active heterohelicenes, curved aromatic diimides and π-conjugated organic diradicals. While planar aromatic diimides are well explored over last decades, a plethora of unique electronic, optical properties can be realized by twisting aromatic diimides into three-dimensional space. Here, we are fascinated to understand the fundamental properties including spin-polarization of these non-planar systems for their potential application in organic electronics, spintronics. We are particularly interested in tweaking 2D-aromatic diimides such as naphthalenediimides (NDI), perylyenediimides (PDI) to create 3D non-planar redox-active chiral polyaromatics such as heterohelicenes, twistacenes and aromatic macrocycles. We utilize rational design approaches to construct the chiral polyaromatics and prepare them using standard organic synthesis methods. A wide range of advanced analytical techniques such as spectroelectrochemical, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), density functional theory (DFT) are implemented for understanding the material properties to a great depth.
• We are also interested in exploring supramolecular chemistry of these helicenes. Using a rational design approach amiphiphilic helicenes (amphihelicenes) are synthesized using standard organic synthesis and self-assembled in appropriate polar/non-polar media. Controlled balance of intermolecular π-π stacking, hydrogen bonding, hydrophobic interactions between amphihelicenes allow us to construct chiral supramolecular nanostructures. A rigour understanding of kinetics of supramolecular process provides control on size, shape and function of the resulting nanostructure. These supramolecular self-assemblies will be studied for applications in CPL emission, electrocatalysis, redox-triggered chiroptical switching, OLEDs and OFETs etc.
• High-spin organic molecules such as organic diradicals for organic spintronics applications is another key interest of the group. π-conjugated organic radicals are open-shell organic molecules with efficient spin-delocalization throughout the conjugated structure and possess unique magnetic, optical and redox characteristics over sterically protected localized organic radicals (eg. nitronyl nitroxide, oxyl) and closed-shell systems. Unlike traditional closed-shell molecules or open-shell organic radicals that typically have singlet (S=0) or doublet (S=1/2) ground state, high-spin organic diradicals possess triplet ground state (S=1) and excited singlet state (S=0).7 Parallel spins (either α or β-spin) with non-zero exchange interaction manifests triplet ground state and fundamental to organic molecule-based ferromagnetism. They potentially exhibit spin-polarization due to ferromagnetic interactions between the spins and in a self-assembled state migration of selective spin (e.g. α-spin) occurs resulting in spin-filtering effect. Few of the examples, crystals of partially oxidized tetrathiafulvalene radical cation (TTF•+) exhibit molecule-based spin-polarization and high conductivity (σRT= 530 Scm-1) promoted by intermolecular π-orbital overlap, low on-site Coulomb repulsion energy. Our interest lies in developing organic diradicals that provide opportunity to achieve combined spin-alignment and selective spin conduction in a single molecular system i.e. co-existence of magnetism and charge transport or simply a conducting magnet.