Helicenes:

Helicenes are ortho-fused polyaromatic compounds with helically twisted non-planar strained structures due to steric repulsions between fjord groups e.g. repulsions between fjord H’s of terminal benzenes in [5]helicenes. The helical topology renders chirality despite no chiral center. Large absorption coefficients together with helical chirality, helicenes exhibit chiroptical properties with excellent circularly polarized light (CPL) absorption and circularly polarized luminescence dissymmetry factors.[1] We are interested in hetero atom (N, O, S, B) doped helicenes called heterohelicenes as they exhibit low band-gaps over carbohelicenes due to stabilized LUMO and they exhibit peculiar redox-activity, fluorescence, photochromism and other interesting properties at molecular level. Our recent results on naphthalenediimides derived hetero[5]helicenes exhibit unique redox behaviour that led to the serendipitous discovery of Zimmerman-Mobius aromaticity across the helical fjord.

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 are studied for applications in CPL emission, electrocatalysis, redox-triggered chiroptical switching, OLEDs and OFETs etc.

Organic radicals:

Open-shell π-conjugated organic molecules with efficient spin-delocalization throughout the conjugated structure possess unique magnetic, optical and redox characteristics over sterically protected localized organic radicals (eg. nitronyl nitroxide, oxyl) and closed-shell systems.[1] Enhanced spin/charge transport due to intermolecular π-π stacking interactions make them potential in advanced technological applications including organic electronics, spintronics, spin-filters, and storage devices.[1] Few of the examples include, crystals of partially oxidized tetrathiafulvalene radical cation (TTF•+) exhibit high conductivity (σRT= 530 Scm-1) due to intermolecular π-orbital overlap and low on-site Coulomb repulsion energy.[2] 1D assembly of mixed valence polycyclic triangulene radicals reported with electrical conductivities up to 125 Scm-1.[3] Our interest lies in developing organic radicals that provide opportunity to achieve combined spin-alignment and electron conduction in a single molecular system i.e. co-existence of magnetism and charge transport or simply a conducting magnet.