Polymorphism and cold crystallization in optically nonlinear N-benzyl-2-methyl-4-nitroaniline crystal studied by X-ray diffraction, calorimetry and Raman spectroscopy

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

“…[17]. The FT-IR spectra of powdered BNA in Nujol suspension and in KBr pellet were recorded in the 380-4000 cm À1 range on a Bruker IFS-88 spectrometer at 2 cm À1 resolution in the temperature range of 11-297 K, applying APD-Displex model CS202 cryostat with a Scientific Instruments Inc., Series 5500 temperature controller.…”

“…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.…”

“…The molecule in orthorhombic crystal lattice [17] is asymmetric (C 1 ), almost L-shaped, with two phenyl rings (tri-(I) and mono(II)-substituted), which are connected by three single bonds -NH-CH 2 -forming bridge (Fig. 1).…”

“…The monoclinic phase is metastable and exhibits monotropic transition to the stable phase at 362 K. The glassy phase of BNA can also be obtained by fast cooling of molten BNA (M p = 375 K). The -NO 2 and -NH groups in the BNA orthorhombic crystal are involved in the formation of weak intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO HBs along three distinct directions [17]. Our previous structure-property relationship studied by X-ray, DSC, FT-NIR, resonance Raman and low temperature emission methods showed that the intermolecular interactions, electrical anharmonicity and vibronic couplings together with a specific molecules arrangement in the crystal lattice are crucial to the optical response [7,17,18].…”

“…The -NO 2 and -NH groups in the BNA orthorhombic crystal are involved in the formation of weak intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO HBs along three distinct directions [17]. Our previous structure-property relationship studied by X-ray, DSC, FT-NIR, resonance Raman and low temperature emission methods showed that the intermolecular interactions, electrical anharmonicity and vibronic couplings together with a specific molecules arrangement in the crystal lattice are crucial to the optical response [7,17,18]. The specific L-shape of BNA molecules in the orthorhombic crystal results in the formation of two N-HÁ Á ÁO HBs chains and enables the intermolecular CT as well as ICT which contribute to the SH efficiency [7,18].…”