1H-NMR, dielectric and calorimetric studies of molecular motions in m-nitroaniline crystal

Probing ferroelectric behaviour in charge-transfer organic meta-nitroaniline

“…3(b) Figure 4 presents the temperature dependence of spontaneous polarization P s along the polar axis in m-NA crystal obtained by the integration of the pyroelectric current during a continuous temperature change with dT=dt ¼ 1 K/min. It is seen that spontaneous polarization in m-NA abruptly disappears above 370 K. This is in a good agreement with the previously reported temperature dependence of dielectric permittivity in m-NA crystals, showing a peculiar peak on the dielectric permittivity 0 and pronounced drop of tan d at about 373 K. 32,33 Additionally, differential scanning calorimetry (DSC) also showed sharp anomalies near 373 K during cooling. Such anomalies together with the reported large temperature hysteresis in DSC curves are commonly associated with a first-order ferroelectric to paraelectric phase transition.…”

“…The obtained electrical conductivity 2:5 Â 10 10 S/m is in a good agreement with the previously reported values. 32 The conductivity mechanism in m-NA is well understood [32][33][34] and is associated with a "hop and turn" mechanism representing protons hopping and reorientational motions of the benzene ring and both substituents. As revealed in Ref.…”

Molecular motions contributions to optical nonlinearity of N-benzyl-2-methyl-4-nitroaniline studied by temperature-dependent FT-IR, 1H NMR spectroscopy and DFT calculations

“…The Raman excitation profiles of lattice Table 2 The calculated and experimentally obtained values of second moment of 1 H NMR line (M 2 ) in BNA solid for rigid structure, methyl, phenyl group rotations and trans-gauche motion of methylene group. The M 2 values in the m-NA, MNA and 4-IP crystals are given for comparison [8,15,16]. Note that M 2 value for m-NA was given for -NH 2 180°p roton jumps.…”

“…It is known that the intermolecular charge transfer (via intermolecular hydrogen bonds, HBs), charged polarons (radical anions), conformational helical packing in crystal, vibrational anharmonicity, vibronic couplings and dynamical disorder (molecular motions) are additional factors which influence nonlinear response [2][3][4][5][6][7][8]. The dynamics of a system can be examined by temperature dependent fourier transform IR (FT-IR) and proton nuclear magnetic resonance ( 1 H NMR) spectroscopies where the activation energy and the correlation time of movement can be estimated.…”

“…This work is a continuation of studies on optically nonlinear (NLO) benzene derivatives crystals such as meta-nitroaniline (m-NA) [3,4,8], 2-methyl-4-nitroaniline (MNA) [6,14,15], 4-isopropylphenol (4-IP) [16] and N-benzyl-2-methyl-4-nitroaniline (BNA) [7,17,18]. The earlier studies showed that the charged polarons (radical anions), dynamic disorder of phenyl ring and both (three) nitro and amine (methyl) substituents leads to the instantaneous helical superstructure in the m-NA [3,4] (MNA [6,15]) and contribute to the SHG in these crystals.…”