Unsymmetrical coumarin-biphenyl hybrids: Self-assembling behaviour and DFT investigations

Abstract

A series of new unsymmetrical coumarin-biphenyl hybrid [1,1′-biphenyl]-4-yl (E)-4-(((7-alkyloxy-2-oxo-2H-chromen-3-yl)imino)methyl)benzoates, BPCE-(2–18) self-assembling molecules have been designed and synthesized. Biphenyl end group at one end of molecules have been linked to the substituted coumarin core through imine and ester mesogenic linking units. Initial members of the series exhibited enantiotropic nematic phase, middle members showed nematic as well as smectogenic behaviour (smectic A) whereas the last member showed only smectogenic behaviour with disappearance of nematic mesophase. In addition, a comparative study has been done with structurally similar mesogens. The study incorporated Density Functional Theory calculations to determine the aspect ratio, dipole moment, and polarizability. These factors influence the terminal and lateral interactions of the compounds. Moreover, computation of molecular electrostatic potential was conducted to examine reactivity concerning both nucleophilic and electrophilic attacks. The theoretical findings were then discussed to validate the experimental data and elucidate the mesomorphic behaviour of the compounds. Additionally, calculations for the energy gap of frontier molecular orbitals, global softness, and chemical hardness were performed to assess the potential suitability of the liquid crystalline compounds for various applications.