Synthesis, photophysical, and theoretical studies on π‐conjugated copolymers based on benzothiadiazole and cyanopyridine acceptor moieties along with other π‐bridge units

다국어 초록 (Multilingual Abstract)

A set of π‐conjugated copolymers were synthesized via Pd‐catalyzed cross‐coupling based on benzothiadiazole and cyanopyridine moieties along with other π‐bridge units (thiophene and/or benzene). Their chemical structures were confirmed by various analytical techniques (elemental, IR, 1H, and 13C NMR analyses). All copolymers showed good solubility in most common organic solvents. Thermogravimetric analysis (TGA) analysis showed their good thermal stability with no significant weight loss up to ~260°C. The estimated optical band gaps for thin films were found to be in the range of 2.25–2.62 eV. It was found that the π‐bridge units (benzene and/or thiophene) significantly affect the molecular architecture and optoelectronic properties of the copolymers. They exhibited good fluorescence in diluted solution where the fluorescence emission spectra were obtained by irradiative excitation at the wavelength in the range of 526.0–532.0 nm. X‐ray diffraction (XRD) revealed that all copolymers exhibited a symmetric halo peak at 2θ = 22.5–23.8° corresponding to the presence of alkyl side chains in addition to a small intensity peak at 2θ of ~43° indicates the existence of some degree of remnant some ranges of crystallinity in the films. Density functional theory (DFT) and time‐dependent DFT (TD‐DFT) calculations were used to assess planarity, electronic structure, and optical absorption properties.
π‐Conjugated copolymers P1‐P4 were readily synthesized via Suzuki cross‐coupling methodology. They are designed as a model of A‐D‐A'‐D' system on the basis of using benzothiadiazole and cyanopyridine moieties along with thiophene and/or benzene as π‐bridge units (D‐π‐A). They exhibited a wide energy band gap and good light absorption and emission. XRD revealed that all copolymers exhibited a symmetric halo peak corresponding to the presence of alkyl side chains. Further, they were subjected to theoretical studies using DFT and TD‐DFT simulations.