⁵⁷Fe Mossbauer Study of Four Ferroene Derivatives in a Smectic B Liquid Crystalline Glass

Abstract

Abstract Two monosubstituted ferroenes [ferroenyl-4′-methoxyaniline (FMA) and ferroeyl-4′-n butylaniline (FBA)] and two disubstituted ferroenes [1-1′-di-n-otanoyl ferroene (DOF) and dibenzyl l,1′-ferroene dicarboxylate (DFD)] were introduced into the smectic B liquid crystalline phase of 4-n-butoxybenzylidene-4′-n-otylaniline (BBOA, or 40.8). The resulting systems (3 solutions and one suspension) were studied by 57Fe Mossbauer spectroscopy in the smectic B glass of BBOA at 77°K. The recoil-free fraction, f, and the line asymmetry of the quadrupole split doublet (given by the area ratio of the π and the [sgrave] transitions Aπ/A[sgrave] ) were observed as functions of the angle 0 between the gamma ray direction and the preferred molecular direction as determined by a 9 kG external magnetic field. Analysis of the Aπ/A[sgrave] versus 0 measurements for solutions of DOF, FBA, and FMA in BBOA confirms a positive electric field gradient (V=) normal to the cyclopentadienyl rings and yields an intra-molecular vibrational anisotropy ∊ M = 0 for DOF and ∊ M = 0.20 for FBA and FMA. The area ratio measurements also give the solute order parameter S as follows: 0.11 for 1.5% and 2.0% DOF in BBOA; 0.27 for l.0% FBA in BBOA; and 0.37 for 1.0% FMA in BBOA. These S values for the solutes are explained in terms of molecular structure and shapes of the solute and the host BBOA molecules. The f versus θ measurements give the lattice contribution (∊L) to the nuclear vibrational ellipsoid. The values obtained for (∊L are 0.04 (FMA); 0.07 (DOF); and 0.12 (FMA). These values are discussed with respect to the shapes and loations of the solute molecules relative to the central-core and end-chain regions of the BBOA molecules. Further. these results are compared to previously reported values for Sn-bearing molecules.