Synthesis, characterization and optoelectronic investigations of bithiophene substituted 1,3,4- oxadiazole derivatives as green fluorescent materials† Narahari Deshapande, a Ningaraddi S. Belavagi, a Manjunath G. Sunagar, a Supreet Gaonkar, a G. H. Pujar, b M. N. Wari, b S. R. Inamdar b and Imtiyaz Ahmed M. Khazi * a A series of novel unsymmetrical bithiophene substituted oxadiazole derivatives 2(a–e) were designed and synthesised by employing palladium catalysed Suzuki cross coupling reaction. These bipolar molecules consist of bithiophene as an electron donor unit (D) and electron transporting oxadiazole as acceptor unit (A). The structural integrity of all the new compounds was confirmed by 1 H NMR, 13 C NMR and GC- MS analysis. The photophysical and electrochemical properties have been studied in detail using UV-Vis absorption, fluorescence spectroscopy and CV measurements. All compounds emit intense green fluorescence with good quantum yields. Density functional theory computations have been carried out to understand the structure–property relationship, the computed values are found to be in good agreement with the experimental results. The results demonstrated that the novel bithiophene containing oxadiazole derivatives could play an important role in organic optoelectronics. Introduction Photoluminescence (PL) of organic compounds has been studied extensively to develop thin, efficient, and stable devices with wide viewing angles and fast response. In recent years, PL of organic materials with excellent characteristics has been exploited for the development and commercialization of display materials. The optoelectronic properties of conjugated poly- cyclic aromatic compounds plays a signicant role in photonic and electronic devices such as organic light-emitting diodes (OLEDs) which exhibit a great potential to revolutionize display technologies in the eld of organic electronics. The most successful and suitable OLEDs are good substitutes for liquid crystal-based devices, 1 because of their comparatively low power consumption, compatibility with large area and exible substrates, and tuneability by molecular structure modica- tion. 2,3 A great deal of research work has been focused on the development of visible light emitting OLEDs for display and lighting applications. 4–7 Compared to other display technolo- gies, OLEDs show their own unique advantages like, easy pro- cessing, self-luminescence, high brightness, high efficiency, low drive voltage, wide viewing angle, high contrast and high-speed response. OLEDs are currently used in long-lived and highly efficient colour displays and also hold unique applications in biological and chemical sensing, 8,9 high-density information storage 10 and full-colour light-emitting displays. 11,12 For the purpose of practical use, they still have several unsolved problems such as operational stability of the devices and colour shi aer operation. Some of these problems could be solved by modication of structural backbone of organic compounds. In designing OLEDs, a luminescent material is required in which electron and hole are recombined resulting in the emission of light. 13–16 By employing donor/acceptor strategy one can improve the device efficiency and operational lifetime along with uorescence properties. 17 In order to achieve high uorescence, small bipolar molecules can be designed by incor- porating electron-withdrawing groups like 1,3,4-oxadiazole, phosphineoxide, triazine and electron-donating groups like carbazole, diphenylamine etc. 18–22 The performance of diodes is closely governed by the number of hole (HT) and electron transporting (ET) moieties. Among all uorescent heterocyclic ring systems, the molecules containing 1,3,4-oxadiazole, play a crucial roles like excellent electron-acceptor, high thermal stability, high quantum yields. They are also used as electron- transporting/hole-blocking materials in OLEDs. 23,24 Indeed, oxa- diazole units advantageously restrict p-conjugation to afford materials with deeply lying highest occupied molecular orbital's (HOMOs) such that the triplet energies (ETs) are high. 25–27 a CPEPA, Department of Chemistry, Karnatak University, Dharwad 580003, Karnataka, India b CPEPA, Department of Physics, Karnatak University, Dharwad 580003, Karnataka, India † Electronic supplementary information (ESI) available. See DOI: 10.1039/c5ra14550c Cite this: RSC Adv. , 2015, 5, 86685 Received 22nd July 2015 Accepted 8th October 2015 DOI: 10.1039/c5ra14550c www.rsc.org/advances This journal is © The Royal Society of Chemistry 2015 RSC Adv., 2015, 5, 86685–86696 | 86685 RSC Advances PAPER