Design, Synthesis and Optoelectronic Properties of Unsymmetrical Oxadiazole Based Indene Substituted Derivatives as Deep Blue Fluoroscent Materials

A series of novel unsymmetrically substituted indene-oxadiazole derivatives (3a-f) have been designed and synthesized by employing palladium catalysed Suzuki cross coupling reaction in high yields. The structural integrity of all the novel compounds was established by H-1, C-13 NMR and LC/MS analysis. These compounds are amorphous in nature and are remarkably stable to long term storage under ambient conditions. The optoelectronic properties have been studied in detail using UV-Vis absorption and Fluorescence spectroscopy. All compounds emit intense blue to green-blue fluoroscence with high quantum yields. Time resolved measurments have shown life times in the range of 1.28 to 4.51 ns. The density functional theory (DFT) calculations were carried out for all the molecules to understand their structure-property relationships. Effect of concentration studies has been carried out in different concentrations for both absorption and emission properties and from this we have identified the optimized fluoroscence concentrations for all these compounds. The indene substituted anthracene-oxadiazole derivative (3f) showed significant red shift (lambda(max) (emi) = 490 nm) and emits intense green-blue fluoroscence with largest stokes shift of 145 nm. This compound also exhibited highest fluoroscence life time (tau) of 4.51 ns, which is very close to the standard dye coumarin-540A (4.63 ns) and better than fluorescein-548 (4.10 ns). The results demonstrated that the novel unsymmetrical indene-substituted oxadiazole derivatives could play important role in organic optoelectronic applications, such as organic light-emitting diodes (OLEDs) or as models for investigating the fluorescent structure-property relationship of the indene-functionalized oxadiazole derivatives.