Optoelectronic characterization and thermoelectric figure of merit optimization of newly Spirothiadiazole- thienothiophene-based Macroheterocyclic compounds

Abstract

This work is concerned with the synthesis of some novel organic compounds, examining their optoelectronic characteristics and experiencing their promises for thermoelectric applications.For this purpose, newly spirothiadiazole-thienothiophene-based macroheterocyclic compounds termed as Kz1-Kz3 have been successfully synthesized. The compound syntheses have been performed by a green approach, including a one-pot condensation of thienothiophene thiohydrazide with different ketones, resulting in good-yielding macrocyclic spiroheterocycles.By using FT-IR, NMR and elemental analyses, the compounds' structures have been confirmed.Thin film optical studies reveal strong absorption and high transparency in UV and vis-NIR spectral ranges, respectively. Depending on the degree of conjugation, the energy gaps range from 2.99 to 3.26 eV with indirect allowed transitions. Dielectric and dispersion studies provided evidence of high refractive index and high polarizability confirming their potential as optoelectronic devices. The thermoelectric studies demonstrated that the samples are n-type semiconductors with negative Seebeck coefficients and temperature-dependent conductivities.The best thermoelectric performance among other compounds with a power factor (PF) of 366 μW m⁻¹ K⁻² and a zT of 0.78 at 493 K after annealing at 200°C for 5 minutes was attained by Kz2 compound. The preliminary outcomes of this work clearly demonstrated the promise of spirothiadiazole-thienothiophene frameworks for use in next-generation flexible, eco-friendly thermoelectric and optoelectronic applications.