  Ferroelectric nematic liquid crystals (NFLCs) are distinguished by their
remarkable polarization characteristics and diverse physical phenomena,
sparking significant interest and excitement within the scientific community.
To date, over 150 NFLC molecules have been developed; however, there are no
reports regarding straight linear polar molecules with a parallel alignment of
the permanent dipole moment and the molecular axis. The straight polar mesogen
nBOE exhibited an enantiotropic NF phase with a wide temperature window (up to
100 K) despite having a longer alkyl chain (up to n = 6) than the critical
alkyl chain length of conventional models. Interestingly, nBOE with a medium
length alkyl chain displayed an exotic phase sequence of NF-HCNF-SmCF during
the elimination of positional displacement among adjacent molecules.
Furthermore, we demonstrate the reflective color modulation of the HCNFLC over
the entire VIS-NIR spectral regime by ultralow E-field (up to 0.14 V um^-1).
