Influence of extended π-conjugated benzheterazoles on the photoluminescent and electroluminescent properties

The influence of extended π-conjugation benzheterazoles on the thermal stability and photoluminescent properties of 1, 2, 4, 5-tetrakis (benzothiazolyl) benzene (TBTB) & 1, 2, 4, 5-tetrakis (benzoxazolyl) benzene (TBOB) compounds is presented here. The absorption spectra recorded show an optical band edge at 400 nm for both the cases. In the case of TBOB, a solvation mediated large shift (of about 130 nm) in the photoluminescence (PL) spectra is observed. The density function theory (DFT) calculations performed for TBOB compound suggest that the typical molecule has a planar geometry with highly localized charge densities, responsible for the experimentally observed large hypsochromic shift in the PL spectra. The results of thermo gravimetric analysis (TGA) performed on TBTB and TBOB compounds indicate thermal stability, with melting points >2000C and decomposition temperatures >5000C. The electrochemical properties of TBTB and TBOB were examined with cyclic voltammeter. The light emitting device fabricated using TBTB compound showed the current density ~0.012 A/cm2 at 14 V, with the turn-on voltage at 7 V.