Insights into the cybotactic nematic phase of bent-core molecules

We present X-ray diffraction evidence for clusters exhibiting a skewed cybotactic supramolecular structure in the nematic phase of the butyloxy-phenyl diester, ODBP-Ph-OC(4), a bent core mesogenic diester of the nonlinear diol 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP). The temperature dependence of the off-meridional four-spot pattern shows that the tilt angle in the cybotactic clusters changes with temperature. The correlation lengths exhibit no evidence of critical behavior but there is no underlying smectic C phase in ODBP-Ph-OC(4). The tilted cybotactic clusters persist throughout the 85 degrees C wide nematic phase, and even remain evident in the supercooled nematic. This inherently biaxial supramolecular structure-clusters of stratified and tilted mesogens-embedded in an otherwise translationally disordered nematic host medium may account for the NMR biaxiality observed in nematic phases of ODBP mesogens.