Abstract
We present the large single crystal growth of a series of donor-p-acceptor (D-pi-A) push-pull chromophores; 4-N, N-dimethylamino-b-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 x 4 x 1 mm(3) 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 (1) over bar, while 1 and 2 crystallize in orthorhombic and monoclinic crystal systems with space groups Pbca and P2(1), respectively. The packing in all the chromophores (except 2) is stabilized by C-H...pi interaction. Thermal analysis shows higher thermal stability for 2 (T-d = 354 degrees C), 3 (T-d = 365 degrees C) and 4 (T-d = 330 degrees C) than 1 (T-d = 240 degrees 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.