Theoretical design, synthesis and third-order non-linear optical properties of thiophene and tetrafluorobenzene based low band gap conducting polymers

•Organic conjugated polymers is expanding primarily due to the possibility of doing modifications and powerful variations in the polymeric backbone.•Donor-Acceptor copolymers P(BT-4FPH), P(TH-4FPH) and P(3METH-4FPH), were designed and synthesized by the direct arylation polymerization method, theoretical investigations were carried out using Gaussian 09 with two levels of density functional theories B3LYP and HSE06.•Results obtained from the HSE06/6–31 G (d,p) basis set was more related to the experimental data. The copolymer was characterized by FT-IR, 1H NMR, and TG.•Among the synthesized copolymers P(BT-4FPH) exhibited a lower band gap both theoretically and experimentally.•The third-order non-linear optical properties were studied by the OA Z-scan technique at 532 nm. Copolymers showed RSA non-linear absorption with a lower optical limiting threshold. Thus, the copolymers developed are promising material for optoelectronic devices. Low band gap donor-acceptor type π-conjugated conducting polymers P(BT-4FPH), P(3METH-4FPH) and P(TH-4FPH) were theoretically designed using Gaussian 09 with two hybrid functionals B3LYP, HSE06/6–31 G (d,p) basis set. Oscillator strength and excitation energy of the monomers were determined by TD-DFT/B3LYP/6–31 G (d,p) method. Copolymers were synthesized by the direct arylation polymerization method. Structural characterization was done by FTIR and 1H NMR spectra. Thermal stabilities of the copolymers were evaluated by TG. The molecular weights of the copolymers were obtained by Gel permeation chromatography. Cyclic voltammetry (CV) was used to observe the electrochemical band gaps of the copolymers. Theoretical observations from HSE06/6–31 G (d,p) method supported the experimental results. Third-order non-linear optical properties and optical limiting effect of the copolymers were studied at different laser intensities using the open-aperture Z-scan technique at 532 nm in DMSO. P(BT-4FPH) exhibited strong optical non-linearity with reverse saturable absorption when compared with P(3METH-4FPH) and P(TH-4FPH) with non-linear absorption coefficient β = 1.20 × 10−8 m/W at 20 µJ. Optical threshold values obtained for the copolymers were low which indicated that the polymers could be used for optical power limiting devices. Among the three synthesized copolymers, P(BT-4FPH) exhibited higher molecular weight, lowest electrochemical band gap and showed strong non-linear absorption with lowest optical threshold value of 0.009 GW/cm2