Liquid crystalline G phase of self assembled donor–acceptor molecules by intermolecular hydrogen bonding S. Salma Begum a , T. Vindhya Kumari a , C. Ravi Shankar Kumar b , S. Sreehari Sastry a, ⁎ a Department of Physics, Acharya Nagarjuna University Nagarjuna Nagar 522510 India b Department of Physics, Institute of Science, GITAM University Visakhapatnam 530045 India abstract article info Article history: Received 20 October 2010 Received in revised form 23 December 2010 Available online 25 February 2011 Keywords: PNBA; NHB; FTIR; Intermolecular hydrogen bonding; Crystal G phase The interaction with donor p-n-alkylbenzoic acid and acceptor nonyl-p-hydroxy benzoate molecules was studied. The likely association of these molecules to complexes is studied by intermolecular hydrogen bonding. The textures are observed by polarizing optical microscope with corresponding transitions confirmed by differential scanning calorimetry. The molecular complexes exhibited enantiotropic crystal G phases in both heating and cooling cycles. The relevant functional groups C O, C–O and OH in formation of molecular complexes are attributed with spectral shifts in infrared spectra and further with absorption studies. The proton NMR studies convinced the structural aspects of hydrogen bonded structure. Crystal parameters were studied with powdered X-ray diffraction. The results show that constituent molecules self organize through intermolecular hydrogen bonding in the formation of crystal G phase. © 2011 Elsevier B.V. All rights reserved. 1. Introduction It is evident that a new class of liquid crystals was initiated with hydrogen bonding [1–5] that gained importance by self assembling process [6,7]. A great deal of work is reported on hydrogen bonded liquid crystals either with mesogenics, non mesogenics or with their combination in generation of new phases leading to supramolecular structures [6–9] due to its stability[10] and directionality [11].These include the doubly hydrogen bonding systems [6], the side chains [8], Schiff bases [12], smallest possible molecules [13], polyoxometalates [14], donor–acceptor groups [15], organic acids[16], benzoic acid derivatives [17], oxadiazole derivatives and dicarboxylic acid [18] and dimers of 4-alkoxy-4 1 stilbazole [19]. In all these processes an intermediate state is reached either minimizing the energy or connected with higher energy that participates in hydrogen bonding leading to supramolecular structures. Considerable progress has been made between the donor–acceptor [15,20,21] molecules cross linked by non covalent interactions [5,22,23] with intermolecular hydrogen bonding and its compatibility to its optical property inducing new thermo dynamical phases [24–27]. Herein we report crystal G phase between the donor COOH group p-n-alkylbenzoic acid where n is alkyl chain from 5 to 10 and acceptor group nonyl-p-hydroxy benzoate with intermolecular hydrogen bonding is shown in Fig. 1. 2. Materials and methods The preparation is performed by dissolving in 1:1 ratio the compounds p-n-alkyl benzoic acids (PNBA) mesogenic in nature and nonyl-p-hydroxy benzoate (NHB) in pyridine under constant stirring for about 4 h approximately at 80 °C. The volume of resultant homogenous mixture was reduced to solid powder by removing excess pyridine by fractional distillation. The crystalline products were dried and re-crystallized by using dichloro-methane and the yield obtained is approximately up to 90%. The free and synthesized molecular complexes (PNBA:NHB) were characterized with texture using Hertel Reuss super-pan II polarizing optical microscope (POM) equipped with optical display (DP10) at scan rate of 0.1°°C/min. Confirmations of transition temperatures and thermal studies involve use of differential scanning calorimeter (DSC) with thermograms recorded by SDT Q600 V8.1 under nitrogen atmosphere at scan rate of 5°°C/min with enthalpies measured in W/g and entropies in WK -1 Mol -1 . The solid state (KBr) FTIR-spectra was recorded on Perkin- Elmer (spectrum bX) series at room temperature from 400 to 4400 cm -1 with resolution 8 cm -1 . The proton nuclear magnetic resonance ( 1 H NMR) spectra were recorded on the Brucker Avance 400 MHz instrument in CDCL 3 with chemical shifts in ppm. X-ray studies were performed at room temperature using Phillips powdered XRD system in determining interplanar spacing(Angstrom units), intensity(arbitrary units) and thickness (Angstrom units) using Scherrer's formula [28]. 3. Results The understanding of phase transition in liquid crystalline complexes is emphasized involving non covalent cross linked Journal of Non-Crystalline Solids 357 (2011) 1745–1749 ⁎ Corresponding author. E-mail address: anusshari@gmail.com (S.S. Sastry). 0022-3093/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2010.12.076 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol