T.N. Ahipa

New 4-(2-(4-alkoxyphenyl)-6-methoxypyridin-4-yl)benzonitriles: synthesis, liquid crystalline behavior and photo physical properties

A new series of luminescent 4-(2-(4-alkoxyphenyl)-6-methoxypyridin-4-yl)benzonitriles containing three ring systems, viz. methoxy pyridine, benzonitrile and alkoxy benzene with variable alkoxy chain length, with bent-core structures were synthesized as potential mesogens and characterized by spectral techniques. Their liquid crystalline behavior was investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and variable temperature powder X-ray diffraction (PXRD) measurements. The study reveals that compounds with shorter chain lengths [i.e. m = 4] exclusively exhibit the nematic phase while compounds with longer chain lengths [i.e. m = 6–14 (only even)] show predominantly the orthorhombic columnar phase. Single crystal X-ray analysis of 4-(2-(4-butyloxy/octyloxyphenyl)-6-methoxypyridin-4-yl)benzonitriles reveals that they possess slightly non-planar unsymmetrical bent structures and their molecular packing consists of nonconventional H-bond interactions; it also explains the observed liquid crystalline phase. An optical study indicates that the title compounds are good blue emitting materials showing absorption and emission bands in the range 335–345 nm and 415–460 nm, respectively. An electrochemical study of 4-(2-(4-octyloxyphenyl)-6-methoxypyridin-4-yl)benzonitrile shows a band gap of 1.89 eV with HOMO and LUMO energy levels of −5.06 and −3.17 eV, respectively. Also, density functional theory (DFT) calculations confirm its optimized geometry, electronic absorption and frontier molecular orbital distributions.

2-Methoxypyridine derivatives: synthesis, liquid crystalline and photo-physical properties

We herein report the design and synthesis of fourteen new bent shaped luminescent mesogens carrying a pyridine core substituted with various polar groups. They possess a slightly non-planar bent conformation with various intermolecular interactions, as evidenced by their single crystal X-ray diffraction study, and exhibit an ambient to elevated temperature liquid crystalline phase (N or Colr), which has been confirmed by differential scanning calorimetry, polarized optical microscopy, and powder X-ray diffraction techniques. In these compounds, the nature of polar substituents influences significantly the formation of the mesophase over a wide thermal range. The appearance of the nematic phase is due to the presence of the lateral CN group attached to the pyridine core and the terminal F or Cl substituent. The formation of a rectangular columnar phase is attributed to the absence of the lateral CN group in the pyridine core and the presence of the terminal Br, NO2 or 4-pyridyl group.

Synthesis, structural analysis and solvatochromic behaviour of 4,6-bis (4-butoxyphenyl)-2-methoxynicotinonitrile mesogen

In this communication, we report the synthesis and characterisation of a new luminescent liquid crystalline material, 4,6-bis (4-butoxyphenyl)-2-methoxynicotinonitrile (3). We have confirmed its structure by Fourier transform infrared and 1H nuclear magnetic resonance spectroscopy, elemental analysis and X-ray single crystal diffraction studies. The newly synthesised compound crystallises in a monoclinic system with the space group C2/c and its cell parameters are found to be a = 25.181(4) Å, b = 15.651(4)Å, c = 12.703(19) Å, V = 4880.4 (16) Å, Z = 8. The results indicate that the presence of weak CH … O and CH … N hydrogen bonding as short-range intermolecular interactions are responsible for the formation of its crystal assembly. The measured torsion angle shows the existence of a distorted structure for the molecule wherein 4-butoxyphenylene ring substituent at the fourth position of the central pyridine ring forms a torsion angle χ[C(4), C(3), C(10), C(19)] of 40.55°. Its liquid crystalline behaviour was investigated with the aid of polarised optical microscopy and differential scanning calorimetry. The study reveals that the compound displays a broad nematic phase in the range of 78–112°C. Further, solution phase optical studies indicate that it is a blue light emitter in different non-polar and polar organic solvents at a concentration of 10−5M.

Rational design of benzodithiophene based conjugated polymers for better solar cell performance

The rational design of conjugated polymers is crucial. As photovoltaic materials they need to be optimized for high-performance polymer solar cells (PSCs). We present a concise review of conjugated polymers based on benzodithiophenes (BDTs). In this account, we have discussed the conjugated polymeric designs of various architectures; consisting of electron rich donor and electron deficient acceptor moieties in the main chain, as well as in the side chains, to facilitate effective intra-molecular charge transfer. We summarize that the application of these polymeric materials drastically influences the power conversion efficiency (PCE) of polymeric solar cells. As of now, PCEs of over 10% are reported for these polymeric materials along with fullerene derivatives.

Hexagonal columnar liquid crystals as a processing additive to a P3HT:PCBM photoactive layer

Morphology of the donor/acceptor network in the photoactive layer is critical in order to optimize the device performance. In the present study, a new trihydrazone-functionalized cyanopyridine (CPTH-D16) demonstrating an ambient temperature hexagonal columnar liquid crystalline phase is introduced into the well-known photoactive layer i.e. P3HT:PCBM as a processing additive towards the construction of an efficient solar cell. Photon absorption and emission properties of the blends in the solution/film state are systematically investigated by UV-visible and fluorescence spectroscopy. Furthermore, surface morphology, the degree of crystallinity, changes in nanostructure, and the conductivity of blend films are determined through epi-fluorescence and atomic force microscopy. It is observed that the addition of the CPTH-D16 liquid crystal drastically increases the TUNA current passing through the P3HT:PCBM film. Here, the structural anisotropic nature of CPTH-D16 material helps to obtain well-ordered morphology with nanostructured crystallite formation as well as enhanced current in the P3HT:PCBM film.

New blue emissive conjugated small molecules with low lying HOMO energy levels for optoelectronic applications

Versatile conjugated small molecules bearing cyanopyridone core (CP1-5), composed of various donor/acceptor moieties at position -4 and -6 have been designed, developed and characterized. Their solvatochromic studies were conducted and analyzed using Lippert-Mataga, Kamlet-Taft and Catalan solvent scales and interesting results were obtained. The polarizability/dipolarity of the solvent greatly influenced the spectra. The electrochemical studies were carried out using cyclic voltammetry to calculate the HOMO-LUMO energy levels. The study revealed that the synthesized conjugated small molecules possess low lying HOMO energy levels which can be exploited for application in various fields of optoelectronics.

Synthesis of cyanopyridine based conjugated polymer

This data file contains the detailed synthetic procedure for the synthesis of two new cyanopyridine based conjugated polymer P1 and P2 along with the synthesis of its monomers. The synthesised polymers can be used for electroluminescence and photovoltaic (PV) application. The physical data of the polymers are provided in this data file along with the morphological data of the polymer thin films. The data provided here are in association with the research article entitled ‘Cyanopyridine based conjugated polymer-synthesis and characterisation’ (Hemavathi et al., 2015) [3].

New luminescent 2-methoxy-6-(4-methoxy-phenyl)-4-p-tolyl-nicotinonitrile: Synthesis, crystal structure, DFT and photophysical studies

In the current communication, we report the synthesis, spectroscopic, crystal structure, DFT and photophysical studies of a new nicotinonitrile derivative, viz. 2-methoxy-6-(4-methoxy-phenyl)-4-p-tolyl-nicotinonitrile (2) as a potential blue light emitting material. The compound 2 was synthesized in good yield via a simple route. The acquired spectral and elemental analysis data were in consistent with the chemical structure of 2. The single crystal study further confirms its three dimensional structure, molecular shape, and nature of short contacts. Its DFT calculations reveal that compound 2 possesses a non-planar structure and its theoretical IR spectral data are found to be in accordance with experimental values. In addition, its UV-visible and fluorescence spectral measurements prove that the compound exhibits good absorption and fluorescence properties. Also, it shows positive solvatochromic effect when the solvent polarity was varied from non-polar to polar.

Microscopic analysis of polymer honeycomb thin film studied by PeakForce TUNA for organic solar cell application

New methodologies connecting molecular structure, self-organization, and nanoelectronics are important for the construction of better bulk heterojunction solar cells. In the present work, large area conjugated polymer honeycomb thin films were prepared from poly {2, 5-bis [3-N, N-diethylamino)-1-oxapropyl]-1, 4-phenylenevinylene} (P1) and EG-C60 (1:1 wt/wt). Further, surface morphology and conductivity of honeycomb thin films were studied using conductive-atomic force microscopy. The morphological studies clearly confirm that the EG-C60 molecules are uniformly present only at the nodes and frames of honeycomb structured blend film (which avoids the formation of exciton pair recombination of polymer), whereas the TUNA current map collected at positive and negative biases reveal holes and electrons collection networks corresponding to donor and acceptor phases at honeycomb thin films. This discovery could find applications in fully exploiting the potential of various material systems, and may open up new op...

Synthesis and mesomorphism of new 2-methoxy-3-cyanopyridine mesogens

In the present paper, we describe the synthesis and characterization of six new bent -shaped molecules carrying the 2-methoxy-3-cyanopyridine as a core possessing an outer phenylene unit at the lengthening arm with different alkoxy chain lengths (C-10 and C-12). Mesomorphic behaviors of the new compounds were investigated using optical polarizing microscope and DSC studies. Also, the effect of structural variables on mesogenic properties was studied. All the new cyanopyridine derivatives showed good liquid crystalline properties and exhibit smectic phase.