Synthesis of nonlinear heteroaromatic donor-acceptor conjugated polymers: Structural, theoretical, electrochemical, and optical properties

This study presents a new class of donor-acceptor (D-A) type NLO-active polymeric materials (P1-4), bearing 3,4-disubstituted thiophene as electron donor and 1,3,4-oxadiazole as electron acceptor units, along with various aromatic spacers, namely: phenylenevinylene (P1), 3,4-ethylenedioxythiophene-EDOT (P2), naphthalene (P3), and biphenyl group (P4). Their optical and electrochemical behavior was thoroughly examined using cyclic voltammetry, UV-visible absorption spectroscopy, fluorescence emission spectroscopy, and Z-scan technique for nonlinear optical assessments. Additionally, Density Functional Theory analysis and Molecular Electrostatic Potential mapping were carried out to understand the charge distribution and electronic structure in the repeating units of polymers. The influence of the incorporated conjugated pi-linkers on their molecular geometry and optoelectronic properties was analyzed to reveal the relationship between molecular structures and optoelectronic characteristics. Interestingly, P1-4 exhibited distinctive electrochemical band gaps, and noteworthy optical limiting behavior attributed to efficient two-photon absorption, demonstrating their potential for optoelectronic and photonic applications. Among the new polymers P1-4, P2 displayed the highest two-photon absorption coefficient.Highlights A class of D-A type polymers with varied aromatic pi-spacers were synthesized. New polymers were characterized as potential optical limiting materials. Electronic and charge distribution properties were studied by DFT and MESP. Optical and electrochemical studies showed suitability for nonlinear optics. TPA values are comparable to those typically found in top-tier NLO materials.