Photophysical, thermal properties, solvatochromism and DFT/TDDFT studies on novel conjugated D-A-π-A-D form of small molecules comprising thiophene substituted 1,3,4-oxadiazole

In this paper, we report the design and synthesis of a series of novel conjugated thiophene substituted 1,3,4-oxadiazole derivatives BSTO-4(a-f) of Donor-Acceptor-π-Acceptor-Donor form by utilizing palladium catalyzed Suzuki cross coupling reaction. Structures were characterized by using spectroscopic techniques namely FT-IR, 1H NMR, 13C NMR and Mass spectra. Their thermal, photophysical and solvatochromic properties were studied in detail. Also, the PL investigations in the solid state were carried out. Furthermore, theoretical calculations such as density functional theory (DFT) were performed to get a better understanding of the intramolecular charge transfer property and electronic structures of the compounds. Experimentally measured optical bandgap values are in the range 3.02 to 3.54 eV. All compounds exhibit Stokes shifts in the range of 2776–3964 cm−1 and fluorescence quantum yields (Φf) in the range of 0.06–0.70 in chloroform. These derivatives exhibit high thermal stability that is the 5% weight loss temperature of derivatives are in the range 178–356 °C and the compounds BSTO-4(b, e and f) had the glass transition temperatures (Tg) at 107 °C, 147 °C and 68 °C, respectively. These results demonstrate that the novel thiophene substituted 1,3,4-oxadiazole compounds are promising candidates for potential applications in development of OLEDs, organic electronic devices/optoelectronic devices.