Room temperature helical fluids in single-component systems

Abstract

Technologically significant chiral nematic (N*) phase is a helicoidal superstructure, that is generally formed by the spontaneous self-assembly of entire chiral mesogens (mostly calamitics) or by the LC mixtures where a chiral dopant is being added to the host nematic (N) phase. However, the stabilization of the N* phase at room temperature solely by chiral mesogens is highly challenging where the molecular designing is rather crucial, and thus scarcely reported. Working in this direction, we have rationally designed, synthesized and characterized new chiral materials namely, non-symmetric dimers derived from cholesterol. Notably, as expected, some of these dimers exhibit room temperature N* phase over a wide thermal range. The exclusive occurrence of N* phase has been evidenced unequivocally with the help of polarized optical microscopy (POM) and differential scanning calorimeter (DSC). The chiroptical property of the phase has been studied by recording circular dichroism (CD) spectra as a function of temperature where the intense bisignate bands (change of sign within the band) were observed. Notably, one of the dimers forms stable gel in an aprotic solvent such as hexadecane. Thus, our study reveals a new molecular architecture to stabilize the technologically important N* phase at ambient temperature.