An investigation on single crystal growth, structural, thermal and optical properties of a series of organic D–π–A push–pull materials

Abstract

We present the large single crystal growth of a series of donor–π–acceptor (D–π–A) push–pull chromophores; 4-N,N-dimethylamino-β-nitrostyrene (1), 2-(4-(dimethylamino)benzylidene)malononitrile (2), ethyl 2-cyano-3-(4-(dimethylamino)phenyl)acrylate (3) and methyl 2-cyano-3-(4-(dimethylamino)phenyl)acrylate (4). Single crystals with good optical transparency were grown from a mixed organic solvent (1 : 1 acetone–methanol) applying slow evaporation techniques, and crystal dimensions up to 17 × 4 × 1 mm³ has been successfully achieved in the case of chromophore 4. A single crystal X-ray diffraction study revealed that two (3 and 4) of them belong to the triclinic crystal system with space group P, while 1 and 2 crystallize in orthorhombic and monoclinic crystal systems with space groups Pbca and P2₁, respectively. The packing in all the chromophores (except 2) is stabilized by C–H⋯π interaction. Thermal analysis shows higher thermal stability for 2 (T_d = 354 °C), 3 (T_d = 365 °C) and 4 (T_d = 330 °C) than 1 (T_d = 240 °C). The thermodynamic and kinetic parameters, such as heat and entropy of fusion, and activation energy have been determined by exploiting DSC and TGA data, respectively. A Lippert–Mataga plot reflects the highest change in dipole moment on excitation from ground state to excited state for chromophore 3 (4.80 D) followed by 4 (4.45 D), 2 (3.59 D) and 1 (3.17 D). We also report the quantum yield of all the chromophores in different organic solvents. In acetonitrile, it is 0.007, 0.014, 0.023 and 0.019 for chromophores 1, 2, 3 and 4; respectively. These studies indicate the potential opto-electronic application of these push–pull chromophores.