Tuning of Photoluminescence Properties of Functional Phthalides for OLED Applications

Abstract

With an objective to develop simple organic systems and tailor their properties for optoelectronic applications, we have synthesized three functionalized phthalide derivatives and have investigated their electroluminescence and photophysical properties under different conditions. These derivatives showed good solubility in common organic solvents and exhibited strong absorption in the range 320–400 nm, having molar extinction coefficient values of ca. 104M 1cm 1. The monomeric solution of these derivatives exhibited very low fluorescence quantum yields (FF) of ca. 0.003–0.04 owing to their inherent structural features such as intramolecular free rotation and decay to the dark triplet states. However, upon complexation with Lewis acids, such as BCl3, these derivatives showed increased fluorescence quantum yields up to ca. 0.21 0.01 and also exhibited aggregation induced emission (AIE) in water/acetonitrile mixtures with the emission yields in the range ca. 0.11–0.16. The morphological analysis of the aggregates through SEM and TEM showed the formation of rod-like structures in 90% water/acetonitrile mixture with an average size of ca. 100 nm. Supporting the observed aggregation induced enhancement in emission properties, these derivatives also exhibited significantly enhanced solid state fluorescence quantum yields of ca. 0.58–0.60. As a representative example, organic light emitting diode (OLED) fabricated using the derivative 3 as the emissive layer showed an efficient electroluminescence centered at 524 nm with a turn on voltage of 9 V, demonstrating thereby their potential use in optoelectronic applications.